CDK11 inhibition induces cytoplasmic p21WAF1 splice variant by p53 stabilisation and SF3B1 inactivation

ABSTRACT: CDK11 is a cyclin-dependent kinase with a role in transcription and RNA splicing and represents a potential target of anticancer treatment. This study investigated the interconnection between CDK11 and the p53 tumour suppressor protein. We show that blocking CDK11 functions with selective OTS964 inhibitor leads to p53 stabilisation through MDM2 downregulation, while the low MDM2 levels are achieved by degradation of MDM2 mRNA. p53 activates the expression of its downstream effector p21WAF1, produced in two isoforms, canonical p21C and recently described alternative p21L. The difference between the two isoforms is in the C-terminus with p21L lacking several functional motifs including a nuclear localisation signal and a PCNA binding motif. Because of the lack of isoform-specific p21 antibodies, the identity of p21L was confirmed with mass spectrometry. Furthermore, we analysed the epitopes of three anti-p21 monoclonal antibodies and identified those that recognise both isoforms and an antibody specific to p21C, making it a valuable tool for future research of p21 isoforms. We compared the ability of both isoforms to block proliferation and showed that p21L partially lost its inhibitory potential and that p21L is also more stable than p21C. Furthermore, we discovered that the trigger for p21L induction is inhibiting the SF3B1 spliceosomal protein. CDK11 activates SF3B1 by phosphorylation and inhibition of both SF3B1 and CDK11 induces p21L. The inhibition of another spliceosomal component SF2/ASF only induces p21C. Moreover, p21L is only induced in the cells with functional p53 protein and p53 knock-out cells lose this ability. We also show that an isoform similar to human p21L is produced in murine cells in response to OTS964. We conclude that p21L might represent a possible mechanism for tumour cells to escape p21-induced mitotic arrest, especially for those with SF3B1 mutations and other alterations in spliceosome functions.

INSTRUMENT(S):

ORGANISM(S): Homo Sapiens (human)

SUBMITTER: Naina Verma  

LAB HEAD: Prof. Lenka Hernychova

PROVIDER: PXD057524 | Pride | 2026-04-06

REPOSITORIES: Pride