AJP - Cell Physiology, Vol 262, Issue 5 C1119-C1124, Copyright © 1992 by American Physiological Society
Localization and differential expression of two isoforms of the tight junction protein ZO-1
E. Willott, M. S. Balda, M. Heintzelman, B. Jameson and J. M. Anderson
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510.
ZO-1 is a peripheral membrane protein of approximately 225 kDa located on
the cytoplasmic side of all tight junctions. ZO-1 cDNA sequencing disclosed
the presence of a 240-bp sequence in only some of the ZO-1 cDNAs studied.
This 240-bp region encoded an inframe insertion of 80 amino acids, named
motif-alpha. Expression of the predicted transcripts in normal rat and
human tissues and in human epithelial cell lines (Caco-2, T84, Hep G2) was
shown by reverse transcription of RNA and then DNA amplification.
Immunoblot analysis showed both protein isoforms were present; however, in
different cell lines, their amounts differed markedly relative to each
other. Immunolocalization at light and ultrastructural levels, using
antibodies generated against motif-alpha or shared sequences flanking it,
indicated both forms localized indistinguishably to tight junctions. These
observations demonstrate the existence and variable expression of ZO-1
isoforms and raise the question whether these isoforms contribute to tight
junction diversity in different epithelia.
