CKI isoforms ? and ? regulate Star-PAP target messages by controlling Star-PAP poly(A) polymerase activity and phosphoinositide stimulation.

ABSTRACT: Star-PAP is a non-canonical, nuclear poly(A) polymerase (PAP) that is regulated by the lipid signaling molecule phosphatidylinositol 4,5 bisphosphate (PI4,5P(2)), and is required for the expression of a select set of mRNAs. It was previously reported that a PI4,5P(2) sensitive CKI isoform, CKI? associates with and phosphorylates Star-PAP in its catalytic domain. Here, we show that the oxidative stress-induced by tBHQ treatment stimulates the CKI mediated phosphorylation of Star-PAP, which is critical for both its polyadenylation activity and stimulation by PI4,5P(2). CKI activity was required for the expression and efficient 3'-end processing of its target mRNAs in vivo as well as the polyadenylation activity of Star-PAP in vitro. Specific CKI activity inhibitors (IC261 and CKI7) block in vivo Star-PAP activity, but the knockdown of CKI? did not equivalently inhibit the expression of Star-PAP targets. We show that in addition to CKI?, Star-PAP associates with another CKI isoform, CKI? in the Star-PAP complex that phosphorylates Star-PAP and complements the loss of CKI?. Knockdown of both CKI isoforms (? and ?) resulted in the loss of expression and the 3'-end processing of Star-PAP targets similar to the CKI activity inhibitors. Our results demonstrate that CKI isoforms ? and ? modulate Star-PAP activity and regulates Star-PAP target messages.

SUBMITTER: Laishram RS 

PROVIDER: S-EPMC3185439 | biostudies-literature | 2011 Oct

REPOSITORIES: biostudies-literature