Submitted on September 29, 2003
Accepted on September 2, 2004
sPAR-3, a splicing variant of PAR-3, shows cellular localization and expression pattern different from that of PAR-3 during enterocyte polarization
Takako Yoshii1, Keiko Mizuno2, Tomonori Hirose2, Atsushi Nakajima1, Hisahiko Sekihara1, and Shigeo Ohno2*
1 The Third Department of Internal Medicine, Yokohama City University School of Medicine, Yokohama, Japan
2 Department of Molecular Biology, Yokohama City University School of Medicine, Yokohama, Japan
* To whom correspondence should be addressed. E-mail: ohnos{at}med.yokohama-cu.ac.jp.
PAR-3 (partitioning-defective) is a scaffold-like PDZ (PSD-95/Dlg/ZO-1) domain-containing protein that
forms a complex with PAR-6 and atypical protein kinase C, 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 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 those of other cell-cell junction proteins, while the expression of sPAR-3 decreases.
Biochemical characterization revealed that sPAR-3 associates with atypical protein kinase C as PAR-3
does. 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 that 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.
