sPAR-3, a splicing variant of PAR-3, shows cellular localization and an expression pattern different from that of PAR-3 during enterocyte polarization

Am J Physiol Gastrointest Liver Physiol. 2005 Mar;288(3):G564-70. doi: 10.1152/ajpgi.00426.2003. Epub 2004 Sep 9.

Abstract

PAR-3 (partitioning-defective) is a scaffold-like PDZ (postsynaptic density-95/discs large/zonula occludens-1) domain-containing protein that forms a complex with PAR-6 and atypical PKC, localizes to tight junctions, and contributes to the formation of functional tight junctions. There are several alternatively spliced isoforms of PAR-3, although their physiological significance remains unknown. In this study, we show that one of the major isoforms of PAR-3, sPAR-3, is predominantly expressed in the Caco-2 cells derived from colon carcinoma and is used as a model to investigate the events involved in the epithelial cell differentiation and cell polarity development. During the polarization of Caco-2 cells, the expression of PAR-3 increases as do those of other cell-cell junction proteins, whereas the expression of sPAR-3 decreases. Biochemical characterization revealed that sPAR-3 associates with atypical PKC, as does PAR-3. On the other hand, immunofluorescence microscopy revealed that sPAR-3 does not concentrate at the cell-cell contact region in fully polarized cells, whereas it concentrates at premature cell-cell junctions. This makes a contrast to PAR-3, which concentrates at tight junctions in fully polarized cells. These results provide evidence suggesting the difference in the role between sPAR-3 and PAR-3 in epithelial cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blotting, Western
  • Caco-2 Cells
  • Carrier Proteins / biosynthesis*
  • Carrier Proteins / genetics*
  • Cell Differentiation / physiology
  • Cell Line
  • Cell Polarity
  • Enterocytes / metabolism*
  • Humans
  • Immunoprecipitation
  • Membrane Proteins
  • Microscopy, Fluorescence
  • Protein Kinase C / metabolism
  • Rabbits
  • Tight Junctions / metabolism

Substances

  • Carrier Proteins
  • Membrane Proteins
  • PARD3B protein, human
  • Protein Kinase C