Intracellular transport and storage of secretory proteins in relation to cytodifferentiation in neoplastic pancreatic acinar cells.

Abstract

The pancreatic acinar carcinoma established in rat by Reddy and Rao (1977, Science 198:78-80) demonstrates heterogeneity of cytodifferentiation ranging from cells containing abundant well-developed secretory granules to those with virtually none. We examined the synthesis intracellular transport and storage of secretory proteins in secretory granule-enriched (GEF) and secretory granule-deficient (GDF) subpopulations of neoplastic acinar cells separable by Percoll gradient centrifugation, to determine the secretory process in cells with distinctly different cytodifferentiation. The cells pulse-labeled with [3H]leucine for 3 min and chase incubated for up to 4 h were analyzed by quantitative electron microscope autoradiography. In GEF neoplastic cells, the results of grain counts and relative grain density estimates establish that the label moves successively from rough endoplasmic reticulum (RER) ~ the Golgi apparatus ~ post-Golgi vesicles (vacuoles or immature granules) --~ mature secretory granules, in a manner reminiscent of the secretory process in normal pancreatic acinar cells. The presence of -40% of the label in association with secretory granules at 4 h postpulse indicates that GEF neoplastic cells retain (acquire) the essential regulatory controls of the secretory process. In GDF neoplastic acinar cells the drainage of label from RER is slower, but the peak label of -20% in the Golgi apparatus is reached relatively rapidly (10 min postpulse). The movement of label from the Golgi to the post-Golgi vesicles is evident; further delineation of the secretory process in GDF neoplastic cells, however, was not possible due to lack of secretory granule differentiation. The movement of label from RER --* the Golgi apparatus --> the post-Golgi vesicles suggests that GDF neoplastic cells also synthesize secretory proteins, but to a lesser extent than the GEF cells. The reason(s) for the inability of GDF cells to concentrate and store exportable proteins remain to be elucidated.IntraceUular aspects of the process of protein secretion have been unraveled in the adult pancreatic exocrine acinar cell by the classical autoradiographic studies of Caro and Palade (4) and . These studies have identified six successive steps in the secretory process namely, synthesis, segregation, intraceUular transport via the Golgi complex, concentration, intracellular storage of discharge (for detailed discussion of this process see references 18 and 27). The existence of such a secretory process in a variety of highly differentiated eucaryotic cell types is now well documented (5,6,8,15,18,27,47). Information regarding the acquisition of various steps of the secretory process during cytodifferentiation is, however, lacking. The studies with developing embryonic rat pancreas have provided a greater understanding of the sequential events involved in the histogenesis, the differentiation of the secretory apparatus, and the regulation of expression of pancreas specific genes in this organ (24,28,42). Further delineation of intrac...

Plasma membrane retrieval in neoplastic pancreatic acinar cells.

“…Accordingly, the cells were considered suitable for plasma membrane internalization studies. The processing of secretory proteins in the freshly dissociated GD and GR cells has been extensively studied in a recent investigation and should be consulted for details (13).…”

Role of the Actin Cytoskeleton in Acinar Cell Protein Secretion

“…However, WASP nucleates a new branch on existing F-actin and proteomic analysis of highly purified ZGM revealed the presence of small GTPases and molecular motors (dynein, myosins) but not actin or other cytoskeletal elements (11,12,33). On the other hand, ultrastructural immunogold localization showed actin in the region of ZG (1,3). Together these results suggest that actin in the ZG region of the cell is either loosely bound or not bound at all to the ZGM.…”