cancer-associated-fibroblasts-from-mouse-mammary-tumors-as-tools-for

Cancer-Associated Fibroblasts from Mouse Mammary Tumors as Tools for Molecular and Computational Studies

A compelling body of research has confirmed the critical role of the tumor microenvironment (TME) in the growth and aggressiveness of breast cancer (BC). ...

University Of Torino

STAT3 is an oncogenic transcription factor exerting its functions both as a canonical transcriptional activator and as a non-canonical regulator of energy metabolism and mitochondrial functions. While both activities are required for cell transformation downstream of different oncogenic stimuli, they rely on different post-translational activating events, namely phosphorylation on either Y705 (nuclear activities) or S727 (mitochondrial functions). Here, we report the discovery of the unexpected STAT3 localization to the endoplasmic reticulum (ER), from where it modulates ER-mitochondria Ca release by interacting with the Ca channel IP3R3 and facilitating its degradation. The release of Ca is of paramount importance for life/death cell decisions, as excessive Ca causes mitochondrial Ca overload, the opening of the mitochondrial permeability transition pore, and the initiation of the intrinsic apoptotic program. Indeed, STAT3 silencing enhances ER Ca release and sensitivity to apoptosis following oxidative stress in STAT3-dependent mammary tumor cells, correlating with increased IP3R3 levels. Accordingly, basal-like mammary tumors, which frequently display constitutively active STAT3, show an inverse correlation between IP3R3 and STAT3 protein levels. These results suggest that STAT3-mediated IP3R3 downregulation in the ER crucially contributes to its anti-apoptotic functions via modulation of Ca fluxes.

STAT3 localizes to the ER, acting as a gatekeeper for ER-mitochondrion Ca fluxes and apoptotic responses.

Myocarditis can lead to autoimmune disease, dilated cardiomyopathy, and heart failure, which is modeled in the mouse by cardiac myosin immunization (experimental autoimmune myocarditis [EAM]). Signal transducer and activator of transcription 3 (STAT3) systemic inhibition exerts both preventive and therapeutic effects in EAM, and STAT3 constitutive activation elicits immune-mediated myocarditis dependent on complement C3 and correlating with activation of the STAT3-interleukin 6 (IL-6) axis in the liver. Thus, liver-specific STAT3 inhibition may represent a therapeutic option, allowing to bypass the heart toxicity, predicted by systemic STAT3 inhibition. We therefore decided to explore the effectiveness of silencing liver Stat3 and C3 in preventing EAM onset and/or the recovery of cardiac functions. We first show that complement C3 and C5 genetic depletion significantly prevents the onset of spontaneous myocarditis, supporting the complement cascade as a viable target. In order to interfere with complement production and STAT3 activity specifically in the liver, we took advantage of liver-specific Stat3 or C3 small interfering (si)RNA nanoparticles, demonstrating that both siRNAs can significantly prevent myocarditis onset and improve the recovery of heart functions in EAM. Our data demonstrate that liver-specific Stat3/C3 siRNAs may represent a therapeutic option for autoimmune myocarditis and suggest that complement levels and activation might be predictive of progression to dilated cardiomyopathy.

Liver-Specific siRNA-Mediated Stat3 or C3 Knockdown Improves the Outcome of Experimental Autoimmune Myocarditis.

In the tumor microenvironment, Cancer Associated Fibroblasts (CAFs) become activated by cancer cells and increase their secretory activity to produce soluble factors that contribute to tumor cells proliferation, invasion and dissemination to distant organs. The pro-tumorigenic transcription factor STAT3 and its canonical inducer, the pro-inflammatory cytokine IL-6, act conjunctly in a positive feedback loop that maintains high levels of IL-6 secretion and STAT3 activation in both tumor and stromal cells. Here, we demonstrate that STAT3 is essential for the pro-tumorigenic functions of murine breast cancer CAFs both in vitro and in vivo, and identify a STAT3 signature significantly enriched for genes encoding for secreted proteins. Among these, ANGPTL4, MMP13 and STC-1 were functionally validated as STAT3-dependent mediators of CAF pro-tumorigenic functions by different approaches. Both in vitro and in vivo CAFs activities were moreover impaired by MMP13 inhibition, supporting the feasibility of a therapeutic approach based on inhibiting STAT3-induced CAF-secreted proteins. The clinical potential of such an approach is supported by the observation that an equivalent CAF-STAT3 signature in humans is expressed at high levels in breast cancer stromal cells and characterizes patients with a shorter disease specific survival, including those with basal-like disease.

STAT3 induces breast cancer growth via ANGPTL4, MMP13 and STC1 secretion by cancer associated fibroblasts.

Embryonic stem cells (ESCs) preserve the unique ability to differentiate into any somatic cell lineage while maintaining their self-renewal potential, relying on a complex interplay of extracellular signals regulating the expression/activity of pluripotency transcription factors and their targets. Leukemia inhibitory factor (LIF)-activated STAT3 drives ESCs' stemness by a number of mechanisms, including the transcriptional induction of pluripotency factors such as Klf4 and the maintenance of a stem-like epigenetic landscape. However, it is unknown if STAT3 directly controls stem-cell specific non-coding RNAs, crucial to balance pluripotency and differentiation. Applying a bioinformatic pipeline, here we identify Lncenc1 in mouse ESCs as an STAT3-dependent long non-coding RNA that supports pluripotency. Lncenc1 acts in the cytoplasm as a positive feedback regulator of the LIF-STAT3 axis by competing for the binding of microRNA-128 to the 3'UTR of the Klf4 core pluripotency factor mRNA, enhancing its expression. Our results unveil a novel non-coding RNA-based mechanism for LIF-STAT3-mediated pluripotency.

Article	Year
STAT3 localizes to the ER, acting as a gatekeeper for ER-mitochondrion Ca fluxes and apoptotic responses. Cell death and differentiation\| PubMed ID: 30042492	2019
Liver-Specific siRNA-Mediated Stat3 or C3 Knockdown Improves the Outcome of Experimental Autoimmune Myocarditis. Molecular therapy. Methods & clinical development\| PubMed ID: 32577433	2020
STAT3 induces breast cancer growth via ANGPTL4, MMP13 and STC1 secretion by cancer associated fibroblasts. Oncogene\| PubMed ID: 35042959	2022
STAT3-dependent long non-coding RNA Lncenc1 contributes to mouse ES cells pluripotency via stabilizing Klf4 mRNA. Briefings in functional genomics\| PubMed ID: 37801430	2024

Daniele Viavattene

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