MOLECULAR CHAPERONES IN PANCREATIC TISSUE - THE PRESENCE OF CPN10, CPN60 AND HSP70 IN DISTINCT COMPARTMENTS ALONG THE SECRETORY PATHWAY OF THE ACINAR-CELLS

Three chaperones, the chaperonins cpn10 and cpn60, and the hsp70 prote in, were revealed by immunochemistry and cytochemistry in pancreatic r at acinar cells. Western immunoblotting analysis of rat pancreas homog enates has shown that antibodies against cpn10, cpn60 and hsp70 protei n recognize single protein bands of 25 kDa, 60 kDa and 70 kDa, respect ively. Single bands for the cpn10 and cpn60 were also detected in panc reatic juice. Immunofluorescence studies on rat pancreatic tissue reve aled a strong positive signal in the apical region of the acinar cells for cpn10 and cpn60, while an immunoreaction was detected at the juxt anuclear Golgi region with the anti-hsp70 antibody. Immunocytochemical gold labeling confirmed the presence of these three chaperones in dis tinct cell compartments of pancreatic acinar cells. Chaperonin 10 and cpn60 were located in the endoplasmic reticulum, Golgi apparatus, cond ensing vacuoles and secretory granules. Interestingly, the labeling fo r both cpn10 and cpn60 followed the increasing concentration gradient of secretory proteins along the RER-Golgi-granule secretory pathway. O n the contrary, the labeling for hsp70 was mainly concentrated in the endoplasmic reticulum and the Golgi apparatus. In the latter, the hsp7 0 was found to be primary located in the trans-most cisternae and to c olocalize with acid phosphatase in the trans-Golgi network. The three chaperones were also present in mitochondria. In view of the rote play ed by the chaperones in the proper folding, sorting and aggregation of proteins, we postulate that hsp70 assists the adequate sorting and pa ckaging of proteins from the ER to the trans-Golgi network while cpn10 and cpn60 play key roles in the proper packaging and aggregation of s ecretory proteins as well as, most probably, in the prevention of earl y enzyme activation in secretory granules.