Protein disulfide isomerase (PDI) catalyzes protein folding and thiol-disulfide interchange reactions. The enzyme is localized in the lumen of endoplasmic reticulum (ER) and is abundant in secretory cells of various tissues. In this study we describe the isolation and characterization from human pancreas of a new protein, PDIp, that is structurally and functionally related to PDIs. PDIp cDNA is 1,659 bp in length and predicts a protein with an open reading frame of 511 amino acids. PDIp amino acid sequence shows 46% identity and 66% similarity to that of human PDI. PDIp possesses two thioredoxin-like active sites (WCGHCQ and WCTHCK) and an endoplasmic reticulum retention signal sequence, KEEL, at the carboxyl terminus. Northern analysis of normal human tissues and various human tumor cell lines revealed PDIp mRNA (2.0 kb) expression only in the normal pancreas. Recombinant PDIp protein catalyzed reductive cleavage of insulin and renaturation of reduced RNaseA. Somatic cell genetics and fluorescence in situ hybridization localized the PDIp gene to the short arm of human chromosome 16. It is concluded that PDIp is a new member of the PDI family and is highly expressed in human pancreas.
A novel tissue-specific cDNA, PDIp, was previously isolated from human pancreas. It encodes a protein that is structurally and functionally related to protein disulfide isomerase (PDI). To compare the expression pattern of PDI and PDIp in human pancreas and liver tissues, we prepared rabbit polyclonal antiserum against a recombinant glutathione-S-transferase-coupled PDIp fusion protein. Western blot analysis revealed that pancreas expresses both PDI and PDIp, whereas liver only expresses PDI. Rabbit antiserum raised against recombinant PDIp immunostained specifically to the acinar cells of human pancreas. Treatment of PDIp with peptide:N-glycosidase F caused PDIp down shift in the NaDodSO4-PAGE gel, indicating that PDIp is a glycoprotein. A 2.0-kb message was detected from mouse pancreas using a human PDIp cDNA probe. Similarly, PDIp glycoprotein was detected in mouse pancreas extract by anti-human PDIp antiserum, suggesting that PDIp is highly conserved in human and mouse pancreas. From these studies, we conclude that the pancreas expresses two members of PDI and that PDIp is a glycoprotein specifically expressed in pancreatic acinar cells.
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