title: Nuclear localization of CPI-17, a protein phosphatase-1 inhibitor protein, affects histone H3 phosphorylation and corresponds to proliferation of cancer and smooth muscle cells.
abstract: CPI-17 (C-kinase-activated protein phosphatase-1 (PP1) inhibitor, 17kDa) is a cytoplasmic protein predominantly expressed in mature smooth muscle (SM) that regulates the myosin-associated PP1 holoenzyme (MLCP). Here, we show CPI-17 expression in proliferating cells, such as pancreatic cancer and hyperplastic SM cells. Immunofluorescence showed that CPI-17 was concentrated in nuclei of human pancreatic cancer (Panc1) cells. Nuclear accumulation of CPI-17 was also detected in the proliferating vascular SM cell culture and cells at neointima of rat vascular injury model. The N-terminal 21-residue tail domain of CPI-17 was necessary for the nuclear localization. Phospho-mimetic Asp-substitution of CPI-17 at Ser12 attenuated the nuclear import. CPI-17 phosphorylated at Ser12 was not localized at nuclei, suggesting a suppressive role of Ser12 phosphorylation in the nuclear import. Activated CPI-17 bound to all three isoforms of PP1 catalytic subunit in Panc1 nuclear extracts. CPI-17 knockdown in Panc1 resulted in dephosphorylation of histone H3 at Thr3, Ser10 and Thr11, whereas it had no effects on the phosphorylation of myosin light chain and merlin, the known targets of MLCP. In parallel, CPI-17 knockdown suppressed Panc1 proliferation. We propose that CPI-17 accumulated in the nucleus through the N-terminal tail targets multiple PP1 signaling pathways regulating cell proliferation.
authors.affiliation: Department of Molecular Physiology and Biophysics, and Kimmel Cancer Center, Thomas Jefferson University, 1020 Locust Street, PA 19107, USA. masumi.eto@jefferson.edu
authors.forename: Masumi
authors.initials: M
authors.lastname: Eto
authors.forename: Jason A
authors.initials: JA
authors.lastname: Kirkbride
authors.forename: Rishika
authors.initials: R
authors.lastname: Chugh
authors.forename: Nana Kofi
authors.initials: NK
authors.lastname: Karikari
authors.forename: Jee In
authors.initials: JI
authors.lastname: Kim
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D049109:Cell Proliferation; D004791:Enzyme Inhibitors / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D006657:Histones / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism / Q000473:pathology; D010190:Pancreatic Neoplasms / Q000378:metabolism / Q000473:pathology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D051381:Rats
chemical_list: D004791:Enzyme Inhibitors; D006657:Histones; D047908:Intracellular Signaling Peptides and Proteins; D009124:Muscle Proteins; C107507:PPP1R14A protein, human; D010750:Phosphoproteins; C491519:Ppp1r14a protein, rat; D010749:Phosphoprotein Phosphatases
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