sPAR-3, a splicing variant of PAR-3, shows cellular localization and an expression pattern different from that of PAR-3 during enterocyte polarization.
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.
Yoshii
Takako
T
The Third Department of Internal Medicine, Yokohama City University School of Medicine, Fuku-ura 3-9, Kanazawa-ku, Yokohama 236-0004, Japan.
Mizuno
Keiko
K
Hirose
Tomonori
T
Nakajima
Atsushi
A
Sekihara
Hisahiko
H
Ohno
Shigeo
S
D000818:Animals; D015153:Blotting, Western; D018938:Caco-2 Cells; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics*; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D016764:Cell Polarity; D020895:Enterocytes / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D008565:Membrane Proteins; D008856:Microscopy, Fluorescence; D011493:Protein Kinase C / Q000378:metabolism; D011817:Rabbits; D019108:Tight Junctions / Q000378:metabolism
D002352:Carrier Proteins; D008565:Membrane Proteins; C471157:PARD3B protein, human; D011493:Protein Kinase C