SIRT1 regulates the phosphorylation and degradation of P27 by deacetylating CDK2 to promote T-cell acute lymphoblastic leukemia progression

Despite marked advances in the clinical therapies, clinical outcome of most T-cell acute lymphoblastic leukemia (T-ALL) patients remains poor, due to the high risk of relapse, even after complete remission. Previous studies suggest that the NAD-dependent deacetylase sirtuin 1 (SIRT1) has a dual role in hematologic malignancies, acting as a tumor suppressor or tumor promoter depending on the tumor type. However, little is known about the expression and functions of SIRT1 in T-ALL leukemogenesis.

Our findings suggest that SIRT1 is a promising target in T-ALL and offer a mechanistic link between the upregulation of SIRT1 and downregulation of p27.

Public RNA-seq data, a Notch1 driven T-ALL mouse model and γ-secretase inhibitor were used to identify SIRT1 expression in T-ALL. We knocked down SIRT1 expression with ShRNAs and assessed the impacts of SIRT1 deficiency on cell proliferation, colony formation, the cell cycle and apoptosis. Transgenic SIRT1 knockout mice were used to determine the function of SIRT1 in vivo. RT-PCR, western blot, co-immunoprecipitation and ubiquitination analyses were used to detect SIRT1, p27 and CDK2 expression and their interactions.

SIRT1 protein expression was positively correlated with the activation of Notch1. Downregulation of SIRT1 expression suppressed the proliferation and colony formation of T-ALL cell lines, which was reversed by SIRT1 overexpression. SIRT1 silencing prolonged the lifespan of T-ALL model mice. We demonstrated that p27 was involved in the downstream mechanism of cell cycle arrest induced by silencing SIRT1. SIRT1 increased the phosphorylation of p27 on Thr187 by deacetylating CDK2 and enhanced the interaction between p27 and SKP2 leading to the degradation of p27.