PITK, a PP1 targeting subunit that modulates the phosphorylation of the transcriptional regulator hnRNP K.
Protein phosphatase-1 (PP1), through interactions with substrate targeting subunits, plays critical roles in the regulation of numerous cellular processes. Herein, we describe a newly identified regulatory subunit (PITK; Phosphatase Interactor Targeting K protein) that specifically targets the catalytic subunit of PP1 to nuclear foci to selectively bind and dephosphorylate the transcriptional regulator heterogeneous nuclear ribonucleoprotein K (hnRNP K) at a regulatory S284 site. Additionally, PITK is phosphorylated in vivo at S1013 and S1017, residues that flank or reside within the PP1C-binding motif, and this phosphorylation negatively regulates the binding of the phosphatase to PITK. A mutant variant, S1013,1017A-PITK, when expressed in intact cells, exhibited an increase in native PP1 binding and elicited a more profound dephosphorylation of hnRNPK at S284. A global analysis of transcription by Affymetrix microarray revealed that the expression of PITK resulted in the altered expression of 47 genes, including a marked induction of MEK5 (>14-fold, p<0.007). Additionally, the effects of PITK and S1013,1017A-PITK on transcription could be modulated by the co-expression of hnRNP K. Taken together, our findings provide a putative mechanism by which transcriptional activity of hnRNP K can be discretely controlled through the regulation of PP1 activity.
Department of Pharmacology and Cancer Biology, Duke University Medical Center, Box 3813, Durham, NC 27710, USA.
Nicole C
NC
Kwiek
Drew F
DF
Thacker
Michael B
MB
Datto
Heather B
HB
Megosh
Timothy A J
TA
Haystead
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D020869:Gene Expression Profiling; D034641:Heterogeneous-Nuclear Ribonucleoprotein K / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D011485:Protein Binding; D054645:Protein Phosphatase 1; D021122:Protein Subunits / Q000378:metabolism*; D011817:Rabbits; D013379:Substrate Specificity; D014158:Transcription, Genetic
C514564:ANKRD28 protein, human; D034641:Heterogeneous-Nuclear Ribonucleoprotein K; D047908:Intracellular Signaling Peptides and Proteins; D021122:Protein Subunits; D010768:Phosphoserine; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1