Embryonal carcinoma (EC) cells, which are considered to be malignant counterparts of embryonic stem cells, comprise the pluripotent stem cell component of teratocarcinomas, a form of testicular germ cell tumors (GCTs). Nevertheless, many established human EC cell lines are nullipotent with limited or no capacity to differentiate under normal circumstances. In this study, we tested whether an over-expression of Yamanaka's reprogramming factors OCT4, SOX2, c-MYC and KLF4 might enable differentiation of the human nullipotent EC cells N2102Ep. Using OCT4 knockdown differentiated N2102Ep cells, we are able to derive reprogrammed N2102Ep cell lines. The induced pluripotency of N2102Ep allows the cells to differentiate toward neural lineage by retinoic acid; the expression of SSEA3 and SSEA4 is down-regulated, whereas that of neural surface markers is up-regulated. Consistent with the up-regulation of neural surface markers, the expression of the master neuroectodermal transcription factor PAX6 is also induced in reprogrammed N2102Ep. We next investigated whether PAX6 might induce spontaneous differentiation of nullipotent stem cells N2102Ep. However, while an ectopic expression of PAX6 promotes differentiation of NTERA2, it induces cell death in N2102Ep. We nevertheless find that upon induction of retinoic acid, the reprogrammed N2102Ep cells form mature neuronal morphology similar to differentiated pluripotent stem cells NTERA2 as determined by TUJ1 expression, which is absent in N2102Ep parental cells. Altogether, we conclude that the nullipotent state of human EC cells can be reprogrammed to acquire a more relaxed state of differentiation potential by Yamanaka's factors.
Keywords: Embryonal carcinoma cell; Induced pluripotency; Nullipotency.
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