Localization and differential expression of two isoforms of the tight junction protein ZO-1.
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.
Willott
E
E
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510.
Balda
M S
MS
Heintzelman
M
M
Jameson
B
B
Anderson
J M
JM
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D005455:Fluorescent Antibody Technique; D006801:Humans; D007365:Intercellular Junctions / Q000378:metabolism*; D007536:Isomerism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014018:Tissue Distribution; D014158:Transcription, Genetic; D062826:Zonula Occludens-1 Protein
D008565:Membrane Proteins; D010750:Phosphoproteins; C569042:TJP1 protein, human; C569044:Tjp1 protein, rat; D062826:Zonula Occludens-1 Protein