ΔNp63α suppresses cell invasion through downregulating Rac1 activity

Abstract

ΔNp63α, a member of the p53 family of transcription factors, is overexpressed in a number of cancers and plays a role in proliferation, differentiation, migration and invasion. We showed previously that ΔNp63α suppresses cell invasion by positively regulating miR-320a, resulting in the downregulation of its direct target protein kinase C gamma (PKCg) and a corresponding reduction in phosphorylated Ras-related C3 botulinum toxin substrate 1 (Rac1). Here, we further show that ΔNp63α inhibits Rac1 GTPase activity. Using a Rac1 pulldown assay to measure Rac1-GTP levels, we showed that silencing ΔNp63α in A431 cells led to a significant upregulation of Rac1-GTP. Silencing ΔNp63α in A431 cells also led to an increase in p21-activated kinase (PAK1) phosphorylation, confirming the negative regulation of ΔNp63α on Rac1. Inhibiting Rac1 GTP activity using EHop-016 led to a significant reduction in both pRac1 and pPAK1 levels. Treatment with Ehop-016 reversed the increase in cell invasion observed upon silencing ΔNp63α. RT-PCR analysis performed on an array of 43 Rac guanine exchange factors (Rac-GEFs) showed that 6 GEFs are significantly upregulated by silencing ΔNp63α in A431 cells. Taken together, our data suggest that ΔNp63α negatively regulates Rac1 GTP activity via downregulation of a Rac-GEF, thereby reducing Rac1-GTP levels and inhibiting cancer cell invasion.