Cell cycle arrest and cell death are controlled by p53-dependent and p53-independent mechanisms in Tsg101-deficient cells

Abstract

Our previous studies have shown that cells conditionally deficient in Tsg101 arrested at the G1/S cell cycle checkpoint and died. We created a series of Tsg101 conditional knock-out cell lines that lack p53, p21Cip1, or p19Arf to determine the involvement of the Mdm2-p53 circuit as a regulator for G1/S progression and cell death. In this new report we show that the cell cycle arrest in Tsg101-deficient cells is p53-dependent, but a null mutation of the p53 gene is unable to maintain cell survival. The deletion of the Cdkn1a gene in Tsg101 conditional knock-out cells resulted in G1/S progression, suggesting that the p53-dependent G1 arrest in the Tsg101 knock-out is mediated by p21Cip1. The Cre-mediated excision of Tsg101 in immortalized fibroblasts that lack p19Arf seemed not to alter the ability of Mdm2 to sequester p53, and the p21-mediated G1 arrest was not restored. Based on these findings, we propose that the p21-dependent cell cycle arrest in Tsg101-deficient cells is an indirect consequence of cellular stress and not caused by a direct effect of Tsg101 on Mdm2 function as previously suggested. Finally, the deletion of Tsg101 from primary tumor cells that express mutant p53 and that lack p21 Cip1 expression results in cell death, suggesting that additional transforming mutations during tumorigenesis do not affect the important role of Tsg101 for cell survival.