Abstract 1301: Post translationally modified EVI1 regulates ΔNp63 to delay cell cycle progression and cell proliferation via the cyclin dependent kinase p21

Abstract

Abstract Several lines of evidence suggest that specific transcriptional events are involved in cell cycle, proliferation and differentiation processes; however, their deregulation by proto-oncogenes are involved in the development of leukemia and tumors. One such proto-oncogene is Ecotropic Viral Integration site I (EVI1) which can differentially effect cell cycle progression and proliferation in cell types of different origin. The proto-oncogene EVI1 which localizes in chromosome 3 (3q26.2) is attracting considerable attention in the recent years because of its reported involvement in late stage chronic myeloid leukemia (CML), high risk myelodysplastic syndrome (both MDS and MDS-AML) and also in de-novo acute myeloid leukemias (AML). Studies also indicate that EVI1 is overexpressed in a subset of human colon cancers, ovarian cancers and that EVI1 might induce disease progression and/or sensitivity to chemotherapy. In this report we provide evidence of a pathway through which EVI1 inhibits cell cycle progression and cell proliferation in HT-29 colon carcinoma cells which was reported earlier to express high levels of the proto-oncogene EVI1. Our bio-informatics analysis and quantified chromatin immunoprecipitation data shows that EVI1 very strongly binds to ΔNp63 promoter element. Deletion mutant analysis revealed that EVI1 binds to ΔNp63 promoter element through its distal zinc finger domain. RQ-PCR and luciferase assay revealed that the binding of EVI1 to ΔNp63 down regulates its expression by ∼4.5 fold and that down regulation of ΔNp63 induces the expression of p21 in HT-29 cells which eventually delay cell cycle progression at G0/G1 phase. Concomitant knocking down of EVI1 with a specific siRNA or transfecting ΔNp63 in EVI1+ cells significantly rescued this phenotype, indicating the growth defect induced by ΔNp63 deficiency to be, at least in part, attributable to EVI1 function. We have reported earlier that EVI1 is post-translationally modified and the modified forms of EVI1 divergently regulate the target genes. Post-translational modification of proteins is a hallmark of signal transduction and it allows existing proteins to react rapidly to extra cellular events cascading to a total cellular response. Interestingly, here we show that EVI1 is phosphorylated and the unphosphorylated form of EVI1 failed to regulate ΔNp63 that eventually showed no change in cell cycle/cell proliferation pattern. Our findings for the first time identify a possible link between two diverse signal transduction pathways acting together in response to a post-translationally modified oncogene that eventually delays cell cycle progression and inhibits cell proliferation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1301. doi:1538-7445.AM2012-1301