Nuclear Export of Yersinia YopM is Mediated by DEAD Box Helicase DDX3 and Regulates Phosphorylation of Nuclear RSK1

Abstract

YopM is an effector protein of Yersinia enterocolitica, Y. pseudotuberculosis and Y. pestis that becomes translocated into target cells by the bacterial type three secretion system and strongly contributes to Yersinia's pathogenicity. Well accepted intracellular activities of the leucin rich repeat (LRR) protein YopM are formation of a complex with the kinases RSK and PKN, which leads to hyperphosphorylation of RSK and accumulation in the nucleus. We identified the DEAD‐box helicase DDX3 as novel interaction partner of YopM and show that YopM and DDX3 form a 2:1 complex, in which two YopM molecules form an interaction surface for DDX3 at their overlapping N‐terminal LRRs. Both, knockdown of DDX3 and inhibition of the exportin CRM1 caused accumulation of YopM in the nucleus, indicating that DDX3 shuttles YopM out of the nucleus via the CRM1 export pathway. YopM induced an increased phosphorylation of RSK1 within the nucleus and blockage of its nuclear export through inhibition of DDX3 or CRM1 further strongly enhanced nuclear RSK1 phosphorylation. These data indicate that YopM is exported from the nucleus by DDX3 and through the ensuing nucleocytoplasmic shuttling the YopM level within the nucleus can be fine tuned. A tight control of YopM's level in the nucleus may be important because it determines phosphorylation and thereby activity of nuclear RSK1, which in turn affects transcription of numerous genes i.e. involved in cell proliferation, ‐cycle and ‐survival.