Cytogenetic characteristics and p53 gene status of human teratocarcinoma PA-1 cells in 407-445 passages

Chromosomal copy number and mutational status are required to authenticate ovarian cancer cell lines as appropriate cell models

BACKGROUND

The mutational status of ovarian cancer cell line IGROV-1 is inconsistent across the literature, suggestive of multiple clonal populations of the cell line. IGROV-1 has previously been categorised as an inappropriate model for high-grade serous ovarian cancer.

METHODS

IGROV-1 cells were obtained from the Netherlands Cancer Institute (IGROV-1-NKI) and the MD Anderson Cancer Centre (IGROV-1-MDA). Cell lines were STR fingerprinted and had their chromosomal copy number analysed and BRCA1/2 genes sequenced. Mutation status of ovarian cancer-related genes were extracted from the literature.

RESULTS

The IGROV-1-NKI cell line has a tetraploid chromosomal profile. In contrast, the IGROV-1-MDA cell line has pseudo-normal chromosomes. The IGROV-1-NKI and IGROV-MDA are both STR matches (80.7% and 84.6%) to the original IGROV-1 cells isolated in 1985. However, IGROV-1-NKI and IGROV-1-MDA are not an STR match to each other (78.1%) indicating genetic drift. The BRCA1 and BRCA2 gene sequences are 100% identical between IGROV-1-MDA and IGROV-1-NKI, including a BRCA1 heterozygous deleterious mutation. The IGROV-1-MDA cells are more resistant to cisplatin and olaparib than IGROV-1-NKI. IGROV-1 has a mutational profile consistent with both Type I (PTEN, PIK3CA and ARID1A) and Type II ovarian cancer (BRCA1, TP53) and is likely to be a Type II high-grade serous carcinoma of the SET (Solid, pseudo-Endometroid and Transitional cell carcinoma-like morphology) subtype.

CONCLUSIONS

Routine testing of chromosomal copy number as well as the mutational status of ovarian cancer related genes should become the new standard alongside STR fingerprinting to ensure that ovarian cancer cell lines are appropriate models.

Role of stress-activated OCT4A in the cell fate decisions of embryonal carcinoma cells treated with etoposide

Tumor cellular senescence induced by genotoxic treatments has recently been found to be paradoxically linked to the induction of “stemness.” This observation is critical as it directly impinges upon the response of tumors to current chemo-radio-therapy treatment regimens. Previously, we showed that following etoposide (ETO) treatment embryonal carcinoma PA-1 cells undergo a p53-dependent upregulation of OCT4A and p21Cip1 (governing self-renewal and regulating cell cycle inhibition and senescence, respectively). Here we report further detail on the relationship between these and other critical cell-fate regulators. PA-1 cells treated with ETO display highly heterogeneous increases in OCT4A and p21Cip1 indicative of dis-adaptation catastrophe. Silencing OCT4A suppresses p21Cip1, changes cell cycle regulation and subsequently suppresses terminal senescence; p21Cip1-silencing did not affect OCT4A expression or cellular phenotype. SOX2 and NANOG expression did not change following ETO treatment suggesting a dissociation of OCT4A from its pluripotency function. Instead, ETO-induced OCT4A was concomitant with activation of AMPK, a key component of metabolic stress and autophagy regulation. p16ink4a, the inducer of terminal senescence, underwent autophagic sequestration in the cytoplasm of ETO-treated cells, allowing alternative cell fates. Accordingly, failure of autophagy was accompanied by an accumulation of p16ink4a, nuclear disintegration, and loss of cell recovery. Together, these findings imply that OCT4A induction following DNA damage in PA-1 cells, performs a cell stress, rather than self-renewal, function by moderating the expression of p21Cip1, which alongside AMPK helps to then regulate autophagy. Moreover, this data indicates that exhaustion of autophagy, through persistent DNA damage, is the cause of terminal cellular senescence.

DNA damage causes TP53-dependent coupling of self-renewal and senescence pathways in embryonal carcinoma cells

Recent studies have highlighted an apparently paradoxical link between self-renewal and senescence triggered by DNA damage in certain cell types. In addition, the finding that TP53 can suppress senescence has caused a re-evaluation of its functional role in regulating these outcomes. To investigate these phenomena and their relationship to pluripotency and senescence, we examined the response of the TP53-competent embryonal carcinoma (EC) cell line PA-1 to etoposide-induced DNA damage. Nuclear POU5F1/OCT4A and P21CIP1 were upregulated in the same cells following etoposide-induced G 2M arrest. However, while accumulating in the karyosol, the amount of OCT4A was reduced in the chromatin fraction. Phosphorylated CHK2 and RAD51/γH2AX-positive nuclear foci, overexpression of AURORA B kinase and moderate macroautophagy were evident. Upon release from G 2M arrest, cells with repaired DNA entered mitoses, while the cells with persisting DNA damage remained at this checkpoint or underwent mitotic slippage and gradually senesced. Reduction of TP53 using sh- or si-RNA prevented the upregulation of OCT4A and P21CIP1 and increased DNA damage. Subsequently, mitoses, micronucleation and senescence were all enhanced after TP53 reduction with senescence confirmed by upregulation of CDKN2A/P16INK4A and increased sa-β-galactosidase positivity. Those mitoses enhanced by TP53 silencing were shown to be multicentrosomal and multi-polar, containing fragmented and highly deranged chromosomes, indicating a loss of genome integrity. Together, these data suggest that TP53-dependent coupling of self-renewal and senescence pathways through the DNA damage checkpoint provides a mechanism for how embryonal stem cell-like EC cells safeguard DNA integrity, genome stability and ultimately the fidelity of self-renewal.