in-vitro-evaluation-oncogenic-transformation-human-mammary-epithelial

In Vitro Evaluation of Oncogenic Transformation in Human Mammary Epithelial Cells

Tumorigenesis is a multi-step process in which cells acquire capabilities&#160;that allow their growth, survival, and dissemination under hostile ...

Universitat Autònoma de Barcelona

In order to examine the relationship between accumulation of residual DNA double-strand breaks (DSBs) and cell death, we have used a control and an ATM (Ataxia-Telangiectasia Mutated) defective cell line, as Ataxia-Telangiectasia (AT) cells tend to accumulate residual DSBs at long times after damage infliction. After irradiation, AT cells showed checkpoint impairment and a fraction of cells displayed an abnormal centrosome number and tetraploid DNA content, and this fraction increased along with apoptosis rates. At all times analyzed, AT cells displayed a significantly higher rate of radiation-induced apoptosis than normal cells. Besides apoptosis, 70-85% of the AT viable cells (TUNEL-negative) carried ≥ 10 γH2AX foci/cell, while only 12-27% of normal cells did. The fraction of AT and normal cells undergoing early and late apoptosis were isolated by flow cytometry and residual DSBs were concretely scored in these populations. Half of the γH2AX-positive AT cells undergoing early apoptosis carried ≥ 10 γH2AX foci/cell and this fraction increased to 75% in late apoptosis. The results suggest that retention of DNA damage-induced γH2AX foci is an indicative of lethal DNA damage, as cells undergoing apoptosis are those accumulating more DSBs. Scoring of residual γH2AX foci might function as a predictive tool to assess radiation-induced apoptosis.

Analysis of Residual DSBs in Ataxia-Telangiectasia Lymphoblast Cells Initiating Apoptosis.

Radiation is used in multiple procedures as a therapeutic and diagnostic tool. However, ionizing radiation can induce mutations in the DNA of irradiated cells, which can promote tumorigenesis. As malignant transformation is a process that takes many years, there are intermediate stages of cells that have initiated the process but have not yet evolved into cancer. The study here aimed to investigate the effect of ionizing radiation on normal and partially transformed human mammary epithelial cells. Breast primary epithelial cells were derived from normal breast tissue from two different donors and modified by transduction with the SV40 small and large T antigen and  genes to obtain partially transformed cells and also with  to completely and experimentally transform them. After exposure to different doses of ionizing radiation, oncogenic features were analyzed by means of an anchorage-independent growth assay and 3D cell culture. The addition of radiation exposure resulted in an increase in the number and size of colonies formed in each of the conditions analyzed and in the reduction of the capacity of partially transformed cells to form properly polarized 3D structures. Moreover, partially transformed cells require lower doses of radiation than healthy cells to enhance anchorage-independent growth capacity. Although cells from different donors have a different degree of sensitivity in the response to radiation, a higher sensitivity to the radiation-induced cell transformation process was observed in those cells that had already initiated the oncogenic process, which require higher doses of radiation to complete the transformation process. IMPLICATIONS: Individuals carrying accumulation of genetic alterations may have an increased susceptibility to radiation-induced neoplastic transformation.

Radiation-Induced Malignant Transformation of Preneoplastic and Normal Breast Primary Epithelial Cells.

Aging is a degenerative process in which genome instability plays a crucial role. To gain insight into the link between organismal aging and DNA repair capacity, we analyzed DNA double-strand break (DSB) resolution efficiency in human mammary epithelial cells from 12 healthy donors of young and old ages. The frequency of DSBs was measured by quantifying the number of γH2AX foci before and after 1Gy of γ-rays and it was higher in cells from aged donors (ADs) at all times analyzed. At 24 hours after irradiation, ADs retained a significantly higher frequency of residual DSBs than young donors (YDs), which had already reached values close to basal levels. The kinetics of DSB induction and disappearance showed that cells from ADs and YDs repair DSBs with similar speed, although analysis of early times after irradiation indicate that a repair defect may lie within the firing of the DNA repair machinery in AD cells. Indeed, using a mathematical model we calculated a constant factor of delay affecting aged human epithelial cells repair kinetics. This defect manifests with the accumulation of DSBs that might eventually undergo illegitimate repair, thus posing a relevant threat to the maintenance of genome integrity in older individuals.

Delayed γH2AX foci disappearance in mammary epithelial cells from aged women reveals an age-associated DNA repair defect.

Aging is associated with changes in gene expression levels that affect cellular functions and predispose to age-related diseases. The use of candidate genes whose expression remains stable during aging is required to correctly address the age-associated variations in expression levels. Reverse transcription quantitative-polymerase chain reaction (RT-qPCR) has become a powerful approach for sensitive gene expression analysis. Reliable RT-qPCR assays rely on the normalisation of the results to stable reference genes. Taken these data together, here we evaluated the expression stability of eight frequently used reference genes in three aging models: oncogene-induced senescence (OIS), in vitro and in vivo aging. Using NormFinder and geNorm algorithms, we identified that the most stable reference gene pairs were PUM1 and TBP in OIS, GUSB and PUM1 for in vitro aging and GUSB and OAZ1 for in vivo aging. To validate these candidates, we used them to normalise the expression data of CDKN1A, APOD and TFRC genes, whose expression is known to be affected during OIS, in vitro and in vivo aging. This study demonstrates that accurate normalisation of RT-qPCR data is crucial in aging research and provides a specific subset of stable reference genes for future aging studies.

Article	Year
Analysis of Residual DSBs in Ataxia-Telangiectasia Lymphoblast Cells Initiating Apoptosis. BioMed research international\| PubMed ID: 27057549	2016
Radiation-Induced Malignant Transformation of Preneoplastic and Normal Breast Primary Epithelial Cells. Molecular cancer research : MCR\| PubMed ID: 30651374	2019
Delayed γH2AX foci disappearance in mammary epithelial cells from aged women reveals an age-associated DNA repair defect. Aging\| PubMed ID: 30875333	2019
Identification of reference genes for RT-qPCR data normalisation in aging studies. Scientific reports\| PubMed ID: 31562345	2019

Teresa Anglada

Biography

JoVE Journal Publications

Other Publications