Secretory vesicle and cell surface markers for human endocrine pancreatic and pituitary tumors.

Abstract

9 1992 Blackwell Scientific Publications, Inc. The pancreatic islet and the adenohypophysis are endocrine tissues sharing several properties. These organs are both composed of different endocrine cells secreting a variety of hormones. These are stored within the cells in dense core secretory vesicles and are released by appropriate stimuli. In addition to dense core secretory vesicles, endocrine pancreatic and adenohypophyseal cells contain small translucent vesicles, which are very similar to synaptic vesicles not only in their morphological appearance but also with regard to their protein constituents [31, 64]. Indeed, several lines of evidence suggest that pancreatic and adenohypophyseal endocrine cells have an additional secretory pathway for neurotransmitters besides the classic exocytotic pathway for hormone release [31, 54, 60]. Proteins present in the dense core vesicles containing hormones, such as chromogranins and secretogranins, have also been detected in their counterparts within neurons (for refs. see [30, 37, 38, 61]). This indicates that neurons and endocrine ceils are very similar with respect to the composition of their characteristic small secretory vesicles (SSV) and large secretory vesicles (LSV) besides having a variety of molecular, biochemical, and functional similarities [25]. Neurons and endocrine cells also share proteins exposed on the external surface. The best documented proteins of this class are members of the family of neural cell adhesion molecules (NCAMs), which are present in endocrine cells of the adult, including pancreatic islet and adenohypophyseal cells [2, 39-41]. While tumors derived from the endocrine pancreas are rare [35], pituitary tumors are frequently observed [27, 35, 73]. Besides symptoms produced locally by the tumors, overproduction of their hormones and their subsequent effects in the body often permit a straightforward diagnosis. However, a significant percentage of endocrine pancreatic and pituitary tumors do not cause elevated serum hormone levels and thus are hormonally inactive [27, 29, 73]. In such cases additional characteristic constituents of endocrine cells are critical in providing information on the nature, location, and distribution of endocrine tumor cells in the body. Here we summarize recent findings concerning the expression of membrane proteins of SSV and of the cell surface antigen NCAM by normal and neoplastic endocrine cells.