Dataset Information

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

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

Laishram Rakesh S RS Barlow Christy A CA Anderson Richard A RA

Nucleic acids research 20110704 18

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, CKIα 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 cri ...[more]

PMID: 21729869

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Project description:Phosphoinositides serve as address labels for recruiting peripheral cytoplasmic proteins to specific subcellular compartments, and as endogenous factors for modulating the activity of integral membrane proteins. Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) is a plasma-membrane (PM)-specific phosphoinositide and a positive cofactor required for the activity of most PM channels and transporters. This requirement for phosphoinositide cofactors has been proposed to prevent PM channel/transporter activity during passage through the biosynthetic/secretory and endocytic pathways. To determine whether intracellularly localized channels are similarly "inactivated" at the PM, we studied PIP(2) modulation of intracellular TRPML1 channels. TRPML1 channels are primarily localized in lysosomes, but can also be detected temporarily in the PM upon lysosomal exocytosis. By directly patch-clamping isolated lysosomes, we previously found that lysosomal, but not PM-localized, TRPML1 is active with PI(3,5)P(2), a lysosome-specific PIP(2), as the underlying positive cofactor. Here we found that "silent" PM-localized TRPML1 could be activated by depleting PI(4,5)P(2) levels and/or by adding PI(3,5)P(2) to inside-out membrane patches. Unlike PM channels, surface-expressed TRPML1 underwent a unique and characteristic run-up upon patch excision, and was potently inhibited by a low micromolar concentration of PI(4,5)P(2). Conversely, depletion of PI(4,5)P(2) by either depolarization-induced activation or chemically induced translocation of 5'-phosphatase potentiated whole-cell TRPML1 currents. PI(3,5)P(2) activation and PI(4,5)P(2) inhibition of TRPML1 were mediated by distinct basic amino acid residues in a common PIP(2)-interacting domain. Thus, PI(4,5)P(2) may serve as a negative cofactor for intracellular channels such as TRPML1. Based on these results, we propose that phosphoinositide regulation sets compartment-specific activity codes for membrane channels and transporters.

Dataset Information

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

Publications

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

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