Juxtamembrane localization of the protein phosphatase-1 inhibitor protein PHI-1 in smooth muscle cells

Nikolaos A. Tountas, James W. Mandell, Allen D. Everett, David L. Brautigan

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)343-350
Number of pages8
JournalHistochemistry and Cell Biology
Issue number4
StatePublished - Apr 2004


  • CPI-17
  • Endothelium
  • Heart
  • Immunohistochemistry
  • Intestine

ASJC Scopus subject areas

  • Histology
  • Molecular Biology
  • Medical Laboratory Technology
  • Cell Biology


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