JoVE   
You do not have subscription access to articles in this section. Learn more about access.

  JoVE Biology

  
You do not have subscription access to articles in this section. Learn more about access.

  JoVE Neuroscience

  
You do not have subscription access to articles in this section. Learn more about access.

  JoVE Immunology and Infection

  
You do not have subscription access to articles in this section. Learn more about access.

  JoVE Clinical and Translational Medicine

  
You do not have subscription access to articles in this section. Learn more about access.

  JoVE Bioengineering

  
You do not have subscription access to articles in this section. Learn more about access.

  JoVE Applied Physics

  
You do not have subscription access to articles in this section. Learn more about access.

  JoVE Chemistry

  
You do not have subscription access to articles in this section. Learn more about access.

  JoVE Behavior

  
You do not have subscription access to articles in this section. Learn more about access.

  JoVE Environment

|   

JoVE Science Education

General Laboratory Techniques

You do not have subscription access to videos in this collection. Learn more about access.

Basic Methods in Cellular and Molecular Biology

You do not have subscription access to videos in this collection. Learn more about access.

Model Organisms I

You do not have subscription access to videos in this collection. Learn more about access.

Model Organisms II

You have trial access to videos in this collection until May 31, 2014.

In JoVE (1)

Other Publications (21)

Articles by Donald J. Vander Griend in JoVE

 JoVE Clinical and Translational Medicine

Formation of Human Prostate Epithelium Using Tissue Recombination of Rodent Urogenital Sinus Mesenchyme and Human Stem Cells

1Department of Surgery, Section of Urology, University of Chicago, 2Committee on Cancer Biology, University of Chicago


JoVE 50327

To unravel the earliest molecular mechanisms underlying prostate cancer initiation, novel and innovative human model systems and approaches are desperately needed. The potential of pre-prostatic urogenital sinus mesenchyme (UGSM) to induce pluripotent stem cell populations to form human prostate epithelium is a powerful experimental tool in prostate research.

Other articles by Donald J. Vander Griend on PubMed

Mitogen-activated Protein Kinase Kinase 4 (MKK4) Acts As a Metastasis Suppressor Gene in Human Ovarian Carcinoma

Despite improvements in chemotherapy and the recognition that aggressive surgical cytoreduction is beneficial, the majority of patients diagnosed with ovarian cancer will die as a result of metastatic disease. The molecular changes associated with acquisition of metastatic ability in ovarian cancer are poorly understood. We hypothesize that metastasis suppressor gene inactivation or down-regulation plays a role in ovarian cancer progression. Mitogen-activated protein kinase kinase 4 (MKK4), a member of the stress-activated protein kinase signaling cascade, has been identified recently as a metastasis-suppressor gene. An immunohistochemical approach was taken to test the possibility that MKK4 dysregulation occurs during the development of clinical ovarian cancer metastases. MKK4 expression was evaluated in normal and metastatic ovarian tissues. Normal ovarian epithelial cells showed high intensity staining for MKK4, whereas metastatic tissues showed a statistically significant decrease in expression. These results support a role for MKK4 dysregulation in the development of clinical disease. A functional approach was taken to test the ability of MKK4 to suppress metastatic colonization, the process whereby disseminated cancer cells lodge and grow at a secondary site in vivo. The SKOV3ip.1 human ovarian cancer cell line was chosen for these studies because it lacks endogenous MKK4 expression but retains both upstream and downstream components of the signaling cascade of MKK4. Ectopic expression of MKK4 in these cells, when injected into female SCID mice, suppressed the number of overt metastatic implants by nearly 90%. Furthermore, MKK4 expression increased the life span of the animals by 70%. Taken together, these data support a role for MKK4 in the suppression of metastatic colonization in ovarian cancer.

MKK4 and Metastasis Suppression: a Marriage of Signal Transduction and Metastasis Research

MAP kinase kinase 4 (MKK4) is a member of the stress-activated protein kinase (SAPK) signaling cascade and is involved in the regulation of many cellular processes. We have recently demonstrated a functional role for MKK4 in the suppression of metastases. In this review, we discuss the established cellular and biochemical functions of MKK4, as well as a new function for MKK4 as a metastasis suppressor gene. Because of the importance of signaling studies to this translational work, a detailed example of the strategy and tools that can be employed to define the biochemical mechanism of MKK4-mediated metastasis suppression is presented. Finally, the potential therapeutic utility of these findings is discussed.

A New Look at an Old Problem: the Survival and Organ-specific Growth of Metastases

Despite improvements in cancer detection and therapy, metastatic disease is largely incurable. Recent research indicates that tumor cells disseminate widely early in the process of pathogenesis, and that the survival and proliferation of these cells--and thus the development of metastases--depend on interactions between the disseminated cells and their particular microenvironment. Proliferative signals and the inhibition of proapoptotic responses are both critically involved in the development of clinically significant metastases. Identification of the underlying signaling cascades may provide additional targets for antimetastatic therapy.

Suppression of Metastasis--a New Function for Known Proteins

Metastasis Suppressor Genes: from Gene Identification to Protein Function and Regulation

In the past decade, findings from various disciplines of research have stimulated a reevaluation of fundamental concepts of the biology of metastasis. The convergence of two avenues of research has largely been responsible for this shift. First, clinical and experimental studies of specific steps of the metastatic cascade have shown that cancer cells often disseminate early in the natural history of disease and can persist at secondary sites for extended periods of time. These findings suggest that disseminated cells remain subject to growth regulation at distant sites as "dormant" single cells or microscopic metastases consisting of small numbers of cells. Second, complementary functional, biochemical, and signal transduction studies have identified a specific class of proteins that suppress the formation of overt metastases. These proteins are encoded by metastasis suppressor genes, which are operationally defined as genes that suppress in vivo metastasis without inhibiting primary tumor growth when expressed ectopically in metastatic cell lines. While metastasis suppressor proteins may affect many steps in metastatic development, recent evidence specifically implicates several of these proteins in the regulation of growth of disseminated cells at secondary sites. This review describes the evolving understanding of rate-limiting steps of metastatic growth, and the role of metastasis suppressor proteins in the regulation of these processes. We will give an overview of the studies of metastasis suppressor protein function, which have shifted our attention toward mechanisms of growth control at the secondary site (i.e., "metastatic colonization"). Emphasis is placed upon the complimentary research in the fields of metastasis and signal transduction that has identified signaling pathways controlling metastatic colonization. We also discuss the regulation of metastasis suppressor proteins and the potential biological and biochemical mechanisms responsible for their organ-type specificity. Finally, the implication of these emerging concepts on the development of therapeutic strategies will be presented.

Suppression of Metastatic Colonization by the Context-dependent Activation of the C-Jun NH2-terminal Kinase Kinases JNKK1/MKK4 and MKK7

Advances in clinical, translational, and basic studies of metastasis have identified molecular changes associated with specific facets of the metastatic process. Studies of metastasis suppressor gene function are providing a critical mechanistic link between signaling cascades and biological outcomes. We have previously identified c-Jun NH2-terminal kinase (JNK) kinase 1/mitogen-activated protein kinase (MAPK) kinase 4 (JNKK1/MKK4) as a prostate cancer metastasis suppressor gene. The JNKK1/MKK4 protein is a dual-specificity kinase that has been shown to phosphorylate and activate the JNK and p38 MAPKs in response to a variety of extracellular stimuli. In this current study, we show that the kinase activity of JNKK1/MKK4 is required for suppression of overt metastases and is sufficient to prolong animal survival in the AT6.1 model of spontaneous metastasis. Ectopic expression of the JNK-specific kinase MKK7 suppresses the formation of overt metastases, whereas the p38-specific kinase MKK6 has no effect. In vivo studies show that both JNKK1/MKK4 and MKK7 suppress the formation of overt metastases by inhibiting the ability of disseminated cells to colonize the lung (secondary site). Finally, we show that JNKK1/MKK4 and MKK7 from disseminated tumor cells are active in the lung but not in the primary tumor, providing a biochemical explanation for why their expression specifically suppressed metastasis while exerting no effect on the primary tumor. Taken together, these studies contribute to a mechanistic understanding of the context-dependent function of metastasis regulatory proteins.

The P38 Kinases MKK4 and MKK6 Suppress Metastatic Colonization in Human Ovarian Carcinoma

Despite considerable efforts to improve early detection of ovarian cancer, the majority of women at time of diagnosis will have metastatic disease. Understanding and targeting the molecular underpinnings of metastasis continues to be the principal challenge in the clinical management of ovarian cancer. Whereas the multistep process of metastasis development has been well established in both clinical and experimental models, the molecular factors and signaling pathways involved in successful colonization of a secondary site by disseminated cancer cells are not well defined. We have previously identified mitogen-activated protein kinase (MAPK) kinase 4/c-Jun NH2-terminal kinase (JNK)-activating kinase (MKK4/JNKK1/SEK1, hereafter referred to as MKK4) as a metastasis suppressor protein in ovarian carcinoma. In this study, we elucidate key mechanisms of MKK4-mediated metastasis suppression. Through the use of a kinase-inactive mutant, we show that MKK4 kinase activity is essential for metastasis suppression and prolongation of animal survival. Because MKK4 can activate either of two MAPKs, p38 or JNK, we expressed MKK6 or MKK7, specific activators of these MAPKs, respectively, to delineate which MAPK signaling module was involved in MKK4-mediated metastasis suppression. We observed that MKK6 expression suppressed metastatic colonization whereas MKK7 had no effect. Our finding that MKK4 and MKK6 both suppress metastasis points to the p38 pathway as an important regulatory pathway for metastatic colonization in ovarian cancer.

Low-calcium Serum-free Defined Medium Selects for Growth of Normal Prostatic Epithelial Stem Cells

Stage-specific differentiation markers were used to evaluate the cellular composition and the origin of nonimmortalized (PrEC) and immortalized (PZ-HPV7, CA-HPV10, RWPE-1, and 957E/hTERT) human prostate cell lines. These studies documented that immortalized and nonimmortalized prostate epithelial cells established and maintained in low (i.e., <300 micromol/L) Ca(2+) serum-free defined (SFD) medium were all derived from normal nonmalignant prostate tissues and contain CD133(+)/ABCG2(+)/alpha(2)beta(1)(Hi)/p63(-)/PSCA(-)/AR(-)/PSA(-) prostate stem cells. In these cultures, prostate stem cells are able to self-renew and generate two distinct cell lineages: the minor proliferatively quiescent neuroendocrine lineage and the major transit-amplifying cell lineage. Subsequently, CD133(-)/ABCG2(-)/alpha(2)beta(1)(Hi)/p63(+)/PSCA(-)/AR(-)/PSA(-) transit-amplifying cells proliferate frequently and eventually mature into proliferatively quiescent CD133(-)/ABCG2(-)/alpha(2)beta(1)(Lo)/p63(-)/PSCA(+)/AR(-)/PSA(-) intermediate cells. Such proliferatively quiescent intermediate cells, however, do not complete their full maturation into CD133(-)/ABCG2(-)/alpha(2)beta(1)(Lo)/p63(-)/PSCA(-)/AR(+)/PSA(+) luminal-secretory cells in low Ca(2+) SFD medium. Addition of universal type I IFN and synthetic androgen (R1881) to culture medium resulted in up-regulation of androgen receptor protein expression. However, it failed to induce full differentiation of intermediate cells into AR(+)/PSA(+) luminal-secretory cells. Our results indicate that such inability of prostate epithelial cells to complete their differentiation is due to continuous expression of Notch-1 receptor and its downstream effector, Hey-1 protein, which actively suppresses differentiation via its ability to transcriptionally repress a series of genes, including the GATA family of transcription factors.

Androgen Receptor As a Licensing Factor for DNA Replication in Androgen-sensitive Prostate Cancer Cells

Androgen receptor (AR) protein expression and function are critical for survival and proliferation of androgen-sensitive (AS) prostate cancer cells. Besides its ability to function as a transcription factor, experimental observations suggest that AR becomes a licensing factor for DNA replication in AS prostate cancer cells and thus must be degraded during each cell cycle in these cells to allow reinitiation of DNA replication in the next cell cycle. This possibility was tested by using the AS human prostate cancer cell lines, LNCaP, CWR22Rv1, and LAPC-4. These studies demonstrated that AR levels fluctuate both within and between various phases of the cell cycle in each of these AS lines. Consistent with its licensing ability, AR is degraded during mitosis via a proteasome-dependent pathway in these AS prostate cancer cells. In contrast, proteasome-dependent degradation of AR during mitosis is not observed in AR-expressing but androgen-insensitive human prostate stromal cells, in which AR does not function as a licensing factor for DNA replication. To evaluate mitotic degradation of AR in vivo, the same series of human AS prostate cancers growing as xenografts in nude mice and malignant tissues obtained directly from prostate cancer patients were evaluated by dual Ki-67 and AR immunohistochemistry for AR expression in mitosis. These results document that AR is also down-regulated during mitosis in vivo. Thus, AS prostate cancer cells do not express AR protein during mitosis, either in vitro or in vivo, consistent with AR functioning as a licensing factor for DNA replication in AS prostate cancer cells.

Stabilizing Androgen Receptor in Mitosis Inhibits Prostate Cancer Proliferation

The androgen receptor (AR) is a steroid transcription factor, the activity of which is the primary focus of androgen ablation therapies for advanced prostate cancer. In prostate cancers, the AR acquires gain-of-function changes allowing it to drive prostate cancer cell survival and proliferation in a cell-autonomous manner. As part of this malignancy-associated gain-of-function, AR acquires a role in licensing for DNA replication in prostate cancer cells. In its role as a licensing factor, AR must be degraded during mitosis in order to allow relicensing in the subsequent cell cycle. This conclusion is supported by the demonstration that acute enhanced expression of AR in prostate cancer cells results in its incomplete degradation in mitosis. This lack of mitotic AR degradation inhibits subsequent cell proliferation due to the inability to relicense all origins of replication needed for the next round of cell division. These data provide a unifying paradigm to clarify a number of unresolved observations in prostate cancer research. In addition, they provide a rationale for a new therapeutic approach for prostate cancer based upon stabilization of AR.

The Role of CD133 in Normal Human Prostate Stem Cells and Malignant Cancer-initiating Cells

Resolving the specific cell of origin for prostate cancer is critical to define rational targets for therapeutic intervention and requires the isolation and characterization of both normal human prostate stem cells and prostate cancer-initiating cells (CIC). Single epithelial cells from fresh normal human prostate tissue and prostate epithelial cell (PrEC) cultures derived from them were evaluated for the presence of subpopulations expressing stem cell markers and exhibiting stem-like growth characteristics. When epithelial cell suspensions containing cells expressing the stem cell marker CD133+ are inoculated in vivo, regeneration of stratified human prostate glands requires inductive prostate stromal cells. PrEC cultures contain a small subpopulation of CD133+ cells, and fluorescence-activated cell sorting-purified CD133+ PrECs self-renew and regenerate cell populations expressing markers of transit-amplifying cells (DeltaNp63), intermediate cells (prostate stem cell antigen), and neuroendocrine cells (CD56). Using a series of CD133 monoclonal antibodies, attachment and growth of CD133+ PrECs requires surface expression of full-length glycosylated CD133 protein. Within a series of androgen receptor-positive (AR+) human prostate cancer cell lines, CD133+ cells are present at a low frequency, self-renew, express AR, generate phenotypically heterogeneous progeny negative for CD133, and possess an unlimited proliferative capacity, consistent with CD133+ cells being CICs. Unlike normal adult prostate stem cells, prostate CICs are AR+ and do not require functional CD133. This suggests that (a) AR-expressing prostate CICs are derived from a malignantly transformed intermediate cell that acquires "stem-like activity" and not from a malignantly transformed normal stem cell and (b) AR signaling pathways are a therapeutic target for prostate CICs.

DNA Licensing As a Novel Androgen Receptor Mediated Therapeutic Target for Prostate Cancer

During middle G(1) of the cell cycle origins of replication orchestrate the ordered assembly of the pre-replication complex (pre-RC), allowing licensing of DNA required for DNA replication. Cyclin-dependent kinase activation of the pre-RC facilitates the recruitment of additional signaling factors, which triggers DNA unwinding and replication, while limiting such DNA replication to once and only once per cell cycle. For both the normal and malignant prostate, androgen is the major stimulator of cell proliferation and thus DNA replication. In both cases, the binding of androgen to the androgen receptor (AR) is required. However, the biochemical cascade involved in such AR-stimulated cell proliferation and DNA synthesis is dramatically different in normal versus malignant prostate cells. In normal prostate, AR-stimulated stromal cell paracrine secretion of andromedins stimulates DNA replication within prostatic epithelial cells, in which AR functions as a tumor suppressor gene by inducing proliferative quiescence and terminal differentiation. By direct contrast, nuclear AR in prostate cancer cells autonomously stimulates continuous growth via incorporation of AR into the pre-RC. Such a gain of function by AR-expressing prostate cancer cells requires that AR be efficiently degraded during mitosis since lack of such degradation leads to re-licensing problems, resulting in S-phase arrest during the subsequent cell cycle. Thus, acquisition of AR as part of the licensing complex for DNA replication represents a paradigm shift in how we view the role of AR in prostate cancer biology, and introduces a novel vulnerability in AR-expressing prostate cancer cells apt for therapeutic intervention.

Amino Acid Containing Thapsigargin Analogues Deplete Androgen Receptor Protein Via Synthesis Inhibition and Induce the Death of Prostate Cancer Cells

There are quantitative and/or qualitative mechanisms allowing androgen receptor (AR) growth signaling in androgen ablation refractory prostate cancer cells. Regardless of the mechanism, agents that deplete AR protein expression prevent such AR growth signaling. Thapsigargin (TG) is a highly cell-penetrant sequiterpene-lactone that once inside cells inhibits (IC(50), ∼ 10 nmol/L) critically important housekeeping SERCA 2b calcium pumps in the endoplasmic reticulum. Using a series of five genetically diverse androgen ablation refractory human prostate cancer lines (LNCaP, LAPC-4, VCaP, MDA-PCa-2b, and CWR22Rv1), TG inhibition of SERCA pumps consistently results in depletion of the endoplasmic reticulum Ca(+2) coupled with μmol/L elevation in the intracellular free Ca(+2) initiating a molecular cascade that: (a) inhibits Cap-dependent AR protein synthesis resulting in 90% depletion of AR protein by 24 hours of TG exposure, (b) arrests the cells in G(0), and (c) induces their apoptotic death. Unfortunately, due to its highly lipophilic nature, TG is not deliverable as a systemic agent without host toxicity. Therefore, TG analogues containing amino acids were developed, which retain ability to deplete AR protein and induce cell death and which can be covalently linked to peptide carriers producing water soluble prodrugs for systemic delivery. Specific amino acid sequences are used to restrict the liberation of cytotoxic amino acid containing TG analogues from the peptide prodrug by prostate-specific proteases, such as prostate-specific antigen and prostate-specific membrane antigen, or cancer-specific proteases, such as fibroblast activation protein, so that toxicity of these prodrugs is selectively targeted to metastatic sites of prostate cancer. Based on these results, these prodrugs are undergoing clinical development.

Dual-label Centromere and Telomere FISH Identifies Human, Rat, and Mouse Cell Contribution to Multispecies Recombinant Urogenital Sinus Xenografts

Recombinant xenografts of human cells growing in immunocompromised rodents are widely used for studying stem cell biology, tumor biology, and epithelial to mesenchyme transitions. Of critical importance is the correct interpretation of the cellular composition of such xenografts.

Cell-autonomous Intracellular Androgen Receptor Signaling Drives the Growth of Human Prostate Cancer Initiating Cells

The lethality of prostate cancer is due to the continuous growth of cancer initiating cells (CICs) which are often stimulated by androgen receptor (AR) signaling. However, the underlying molecular mechanism(s) for such AR-mediated growth stimulation are not fully understood. Such mechanisms may involve cancer cell-dependent induction of tumor stromal cells to produce paracrine growth factors or could involve cancer cell autonomous autocrine and/or intracellular AR signaling pathways.

Loss of Androgen Receptor-dependent Growth Suppression by Prostate Cancer Cells Can Occur Independently from Acquiring Oncogenic Addiction to Androgen Receptor Signaling

The conversion of androgen receptor (AR) signaling as a mechanism of growth suppression of normal prostate epithelial cells to that of growth stimulation in prostate cancer cells is often associated with AR mutation, amplification and over-expression. Thus, down-regulation of AR signaling is commonly therapeutic for prostate cancer. The E006AA cell line was established from a hormone naïve, localized prostate cancer. E006AA cells are genetically aneuploid and grow equally well when xenografted into either intact or castrated male NOG but not nude mice. These cells exhibit: 1) X chromosome duplication and AR gene amplification, although paradoxically not coupled with increased AR expression, and 2) somatic, dominant-negative Serine-599-Glycine loss-of-function mutation within the dimerization surface of the DNA binding domain of the AR gene. No effect on the growth of E006AA cells is observed using targeted knockdown of endogenous mutant AR, ectopic expression of wild-type AR, or treatment with androgens or anti-androgens. E006AA cells represent a prototype for a newly identified subtype of prostate cancer cells that exhibit a dominant-negative AR loss-of-function in a hormonally naïve patient. Such loss-of-function eliminates AR-mediated growth suppression normally induced by normal physiological levels of androgens, thus producing a selective growth advantage for these malignant cells in hormonally naïve patients. These data highlight that loss of AR-mediated growth suppression is an independent process, and that, without additional changes, is insufficient for acquiring oncogene addiction to AR signaling. Thus, patients with prostate cancer cells harboring such AR loss-of-function mutations will not benefit from aggressive hormone or anti-AR therapies even though they express AR protein.

Building on the Foundation of Daring Hypotheses: Using the MKK4 Metastasis Suppressor to Develop Models of Dormancy and Metastatic Colonization

The identification of a novel metastasis suppressor function for the MAP Kinase Kinase 4 protein established a role for the stress-activated kinases in regulating the growth of disseminated cancer cells. In this review, we describe MKK4's biological mechanism of action and how this information is being used to guide the development of new models to study cancer cell dormancy and metastatic colonization. Specifically, we describe the novel application of microvolume structures, which can be modified to represent characteristics similar to those that cancer cells experience at metastatic sites. Although MKK4 is currently one of many known metastasis suppressors, this field of research started with a single daring hypothesis, which revolutionized our understanding of metastasis, and opened up new areas of exploration for basic research. The combination of our increasing knowledge of metastasis suppressors and such novel technologies provide hope for possible clinical interventions to prevent suffering from the burden of metastatic disease.

Deregulation of a Hox Protein Regulatory Network Spanning Prostate Cancer Initiation and Progression

The aberrant activity of developmental pathways in prostate cancer may provide significant insight into predicting tumor initiation and progression, as well as identifying novel therapeutic targets. To this end, despite shared androgen-dependence and functional similarities to the prostate gland, seminal vesicle cancer is exceptionally rare.

Growth Kinetics of CD133-positive Prostate Cancer Cells

In the adult human prostate CD133 expression is thought to mark rare prostate epithelial stem cells and malignant tumor stem/initiating cells. Such putative stem cell populations are thought to proliferate slowly, but possess unlimited proliferative potential. Based on this, we hypothesized that CD133(pos) prostate cancer cells proliferate slower than CD133(neg) cells.

Sox2 is an Androgen Receptor-repressed Gene That Promotes Castration-resistant Prostate Cancer

Despite advances in detection and therapy, castration-resistant prostate cancer continues to be a major clinical problem. The aberrant activity of stem cell pathways, and their regulation by the Androgen Receptor (AR), has the potential to provide insight into novel mechanisms and pathways to prevent and treat advanced, castrate-resistant prostate cancers. To this end, we investigated the role of the embryonic stem cell regulator Sox2 [SRY (sex determining region Y)-box 2] in normal and malignant prostate epithelial cells. In the normal prostate, Sox2 is expressed in a portion of basal epithelial cells. Prostate tumors were either Sox2-positive or Sox2-negative, with the percentage of Sox2-positive tumors increasing with Gleason Score and metastases. In the castration-resistant prostate cancer cell line CWR-R1, endogenous expression of Sox2 was repressed by AR signaling, and AR chromatin-IP shows that AR binds the enhancer element within the Sox2 promoter. Likewise, in normal prostate epithelial cells and human embryonic stem cells, increased AR signaling also decreases Sox2 expression. Resistance to the anti-androgen MDV3100 results in a marked increase in Sox2 expression within three prostate cancer cell lines, and in the castration-sensitive LAPC-4 prostate cancer cell line ectopic expression of Sox2 was sufficient to promote castration-resistant tumor formation. Loss of Sox2 expression in the castration-resistant CWR-R1 prostate cancer cell line inhibited cell growth. Up-regulation of Sox2 was not associated with increased CD133 expression but was associated with increased FGF5 (Fibroblast Growth Factor 5) expression. These data propose a model of elevated Sox2 expression due to loss of AR-mediated repression during castration, and consequent castration-resistance via mechanisms not involving induction of canonical embryonic stem cell pathways.

Stress Response Protein RBM3 Attenuates the Stem-like Properties of Prostate Cancer Cells by Interfering with CD44 Variant Splicing

Stress response pathways play an important role in cancer. The cold-inducible RNA-binding protein RBM3 is upregulated in several types of cancer including prostate cancer (PCa), but its pathogenic contributions are undetermined. RBM3 is expressed at low basal levels in human fetal prostate or in CD133+ prostate epithelial cells (PrEC), compared to the adult prostate or to CD133- PrEC, and RBM3 is downregulated in cells cultured in soft agar or exposed to stress. Notably, RBM3 overexpression in prostate cancer cells attenuated their stem cell-like properties in vitro as well as their tumorigenic potential in vivo. Interestingly, either overexpressing RBM3 or culturing cells at 32ºC suppressed RNA splicing of the CD44 variant v8-v10 and increased expression of the standard CD44 (CD44s) isoform. Conversely, silencing RBM3 or culturing cells in soft agar (under conditions that enrich for stem cell-like cells) increased the ratio of CD44v8-v10 to CD44s mRNA. Mechanistic investigations showed that elevating CD44v8-v10 interfered with MMP9-mediated cleavage of CD44s and suppressed expression of cyclin D1, whereas siRNA-mediated silencing CD44v8-v10 impaired the ability of prostate cancer cells to form colonies in soft agar. Together these findings suggested that RBM3 contributed to stem cell-like character in prostate cancer by inhibitingCD44v8-v10 splicing. Our work uncovers a hitherto unappreciated role of RBM3 in linking stress-regulated RNA splicing to tumorigenesis, with potential prognostic and therapeutic implications in prostate cancer.

Waiting
simple hit counter