INTRACISTERNAL CRYSTALS IN PANCREATIC ACINAR-CELLS - FAILURE IN THE DISTINCT AGGREGATION OF SECRETORY PROTEINS

Mechanisms leading to the formation of crystalline inclusions in the c isternal space of the rough endoplasmic reticulum are poorly understoo d. This phenomenon was investigated in pancreatic acinar cells using t wo different experimental models: 1) Intraperitoneal injection of DL-p -chlorophenylalanine methyl ester, and 2) culture of isolated acinar c ells within the Matrigel basement membrane in the presence of 2% dimet hyl sulfoxide. Features and composition of induced crystals were analy zed by protein A-gold and lectin-gold cytochemistry, electron microsco pe autoradiography, electron energy loss spectroscopic imaging and ene rgy dispersive X-ray analysis. Crystal formation occurred in ribosome partially free rough endoplasmic reticulum (RER) regions and was simil ar in both experimental protocols. The protein A-gold revealed the pre sence of nine major pancreatic enzymes in the crystals. However, the l abeling intensities varied among enzymes with higher concentrations of amylase than chymotrypsinogen when compared to the secretory granules . Concanavalin A and Helix pomatia labelings were weak over the crysta ls and did not correspond to those of RER or secretory granules. Sulfu r contents in crystals were lower than phosphorus and their ratio was opposite to the one found in secretory granules. Electron microscope a utoradiography demonstrated incorporation of radiolabeled leucine and presence of newly synthesized proteins in the crystals. Furthermore, c ells containing both crystals and secretory granules displayed silver grains in most of the cellular compartments involved in secretion. Thu s, failure in the normal concentration and sorting process of secretor y proteins leading to crystal formation includes changes in protein gl ycosylation and decrease of disulfide bond formation while retaining s ecretory capabilities.