A LYSOPHOSPHOLIPASE SPECIFIC FOR EXOCRINE PANCREATIC-CELLS IS STORED IN ZYMOGEN GRANULES AND SECRETED INTO PANCREATIC-JUICE

  • 1 April 1990
    • journal article
    • research article
    • Vol. 51  (2) , 242-251
Abstract
We separated by two-dimensional (2D) gel electrophoresis the content of isolated rat zymogen granules and from the gel excised a protein of apparent MW 77,500 and an isoelectric point of about 4.7. A rabbit antiserum against this previously uncharacterized rat zymogen granule protein recognized two cDNA clones in a rat pancreas expression library. The cDNA inserts of these two clones had sequences showing perfect homology to the published cDNA sequence of rat pancreatic lysophospholipase. The antiserum recognized only a single protein, lysophospholipase, on one and two-dimensional immunoblots of rat pancreas homogenates and isolated zymogen granules. The antiserum did not react with any protein in homogenates of rat liver, spleen, adrenal, parotid, and prostate tissue. The zymogen granule protein of the guinea pig, previously identified as Lipase 1, was recognized specifically by the antiserum against rat lysophospholipase. This guinea pig protein can now be regarded as lysophospholipase. The same protein was demonstrated in the transformed rat acinar cell line AR4-2J, where both the rate of total enzyme synthesized and the amount of mRNA increased following treatment with dexamethasone. Immunogold labeling established that pancreatic lysophospholipase is restricted exclusively to exocrine cells where it occurs only in compartments of the exocytotic pathway. It could also be detected in pancreatic juice in the ducts of the tissue. Finally, we have shown that lysophospholipase is not related to the zymogen granule membrane protein GP2. This work establishes that lysophospholipase is a normal member of the set of soluble enzymes and proenzymes that are stored in zymogen granules and secreted into pancreatic juice.