TPX2 Induces Mitotic Survival via BCL2L1 Induction Through YAP1 Protein Stabilization in Human Embryonic Stem Cells

Abstract

Genetic alterations have been reported in most human embryonic stem cells (hESCs) for decades. ‘Survival advantage,’ a typical trait acquired during long-term in vitro culture, results from induction of BCL2L1 upon frequent copy number variation (CNV) at locus 20q11.21 and is one of the strongest candidates associated with genetic alteration via escape from mitotic stress. However, the underlying mechanisms for BCL2L1 induction remain undefined. Furthermore, abnormal mitosis and ‘survival advantage’ frequently occurring in the late passage are respectively associated with the expression of TPX2 and BCL2L1, which are located in locus 20q11.21. In this study, we observed that 20q11.21 CNV was not sufficient for BCL2L1 induction and consequent survival traits in pairs of hESCs and human induced pluripotent stem cells (iPSCs) with normal and 20q11.21 CNVs. Inducible expression of TPX2 and basal TPX2 expression due to leakage of the inducible system in hESCs with normal copy number was sufficient to promote BCL2L1 expression and promoted high tolerance to mitotic stress. High Aurora A kinase activity by TPX2 stabilized YAP1 protein to promote YAP1 dependent BCL2L1 expression. Thus, a chemical inhibitor of Aurora A kinase and knockdown of YAP/TAZ significantly abrogated the aforementioned high tolerance to mitotic stress through BCL2L1 suppression. These results suggest that the collective expression of TPX2 and BCL2L1 from CNV at loci 20q11.21 and a consequent increase in YAP1 signaling would promote genome instability during long-term in vitro hESC culture.