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miR-302 is the major microRNA found in human embryonic stem cells and induced pluripotent stem cells, but its function has been unclear. In mice, there is evidence that miR-302 may silence p21Cip1 (CDKN1A) to promote cell proliferation, whereas studies in human reprogrammed pluripotent stem cells suggested that elevated miR-302 expression inhibited cell cycle transit. Here, we clarify this difference, reporting that in human cells, miR-302 simultaneously suppressed both the cyclin E-CDK2 and cyclin D-CDK4/6 pathways to block>70% of the G1-S cell cycle transition. Concurrent silencing of BMI-1, a cancer stem cell marker targeted by miR-302, further promoted tumor suppressor functions of p16Ink4a and p14/p19Arf directed against CDK4/6-mediated cell proliferation. Among all G1 phase checkpoint regulators, human p21Cip1 was found not to be a valid target of miR-302. Overall, our findings indicate that miR-302 inhibits human pluripotent stem cell tumorigenicity by enhancing multiple G1 phase arrest pathways rather than by silencing p21Cip1.
Lin et al. (Tue,) studied this question.