Histochemistry and Cell Biology

, Volume 121, Issue 4, pp 343–350 | Cite as

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
Original Paper


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.


CPI-17 Intestine Endothelium Heart Immunohistochemistry 



We would like to thank Jan Redick of the University of Virginia Advanced Microscopy Facility for assistance with confocal and electron microscopy. This research was supported by grants (to D.L.B.) CA40042 from the National Cancer Institute and GM56362 from the National Institute of General Medical Sciences, US Public Health Service.


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Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • Nikolaos A. Tountas
    • 1
  • James W. Mandell
    • 2
  • Allen D. Everett
    • 3
    • 4
  • David L. Brautigan
    • 1
  1. 1.Center for Cell SignalingUniversity of Virginia School of MedicineCharlottesvilleUSA
  2. 2.Department of Pathology (Neuropathology)University of Virginia Health SystemCharlottesvilleUSA
  3. 3.Department of Pediatrics and the Cardiovascular Research CenterUniversity of Virginia Health SystemCharlottesvilleUSA
  4. 4.Department of PediatricsJohns Hopkins School of MedicineBaltimoreUSA

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