title: Juxtamembrane localization of the protein phosphatase-1 inhibitor protein PHI-1 in smooth muscle cells.
abstract: Protein phosphorylation regulates many fundamental processes and protein phosphatase-1 (PP1) is a major phosphatase that determines the levels of Ser/Thr phosphorylation. Regulatory subunits and inhibitor phosphoproteins control PP1 activity. PHI-1 is a member of a family of PP1 inhibitor phosphoproteins that was discovered based on sequence similarity to the known inhibitor CPI-17. To learn more about PHI-1 we determined the tissue distribution of PHI-1 in embryonic and adult tissues, and examined its cellular localization by immunohistochemistry. In the embryo PHI-1 appeared first in the heart at E10, and by E15 it was detected in multiple tissues. Expression in adult tissues was strikingly different, with PHI-1 detected primarily in smooth muscles in the intestine, blood vessels, and male and female genitourinary tracts. PHI-1 also was highly expressed in the endothelial layer of blood vessels. Both PHI-1 and CPI-17 are expressed predominantly in adult smooth muscles. Whereas CPI-17 staining was diffuse PHI-1 was concentrated along the cell membrane in distinct foci, detected by confocal and electron microscopy. The common tissue distribution but different cellular localization of PHI-1 and CPI-17 suggest distinctive physiological roles for these two PP1 inhibitors.
authors.affiliation: Center for Cell Signaling, University of Virginia School of Medicine, PO Box 800577, Charlottesville, VA 22908, USA.
authors.forename: Nikolaos A
authors.initials: NA
authors.lastname: Tountas
authors.forename: James W
authors.initials: JW
authors.lastname: Mandell
authors.forename: Allen D
authors.initials: AD
authors.lastname: Everett
authors.forename: David L
authors.initials: DL
authors.lastname: Brautigan
mesh_terms: D000367:Age Factors; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D004622:Embryo, Mammalian; D004730:Endothelium, Vascular / Q000166:cytology; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D051379:Mice; D008854:Microscopy, Electron; D009124:Muscle Proteins / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000737:chemistry*; D010749:Phosphoprotein Phosphatases; D010750:Phosphoproteins / Q000378:metabolism; D054645:Protein Phosphatase 1; D011506:Proteins / Q000378:metabolism*; D014018:Tissue Distribution
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D009124:Muscle Proteins; C107507:PPP1R14A protein, human; D010750:Phosphoproteins; C491520:Ppp1r14a protein, mouse; D011506:Proteins; C073882:phosphoprotein phosphatase inhibitor 1; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1