A NEUROENDOCRINE-SPECIFIC PROTEIN LOCALIZED TO THE ENDOPLASMIC-RETICULUM BY DISTAL DEGRADATION

Citation
Mr. Schiller et al., A NEUROENDOCRINE-SPECIFIC PROTEIN LOCALIZED TO THE ENDOPLASMIC-RETICULUM BY DISTAL DEGRADATION, The Journal of biological chemistry, 270(44), 1995, pp. 26129-26138
Citations number
91
Categorie Soggetti
Biology
ISSN journal
00219258
Volume
270
Issue
44
Year of publication
1995
Pages
26129 - 26138
Database
ISI
SICI code
0021-9258(1995)270:44<26129:ANPLTT>2.0.ZU;2-D
Abstract
Regulated endocrine-specific protein, 18-kDa (RESP18), was previously cloned from rat neurointermediate pituitary based on its coordinate re gulation with proopiomelanocortin and neuroendocrine specificity. RESP 18 has no homology to any known protein. Although RESP18 is translocat ed across microsomal membranes after in vitro translation, AtT-20 pitu itary tumor cells, which endogenously synthesize RESP18, do not releas e it into the culture medium. In this work, immunostaining and subcell ular fractionation have identified RESP18 as an endoplasmic reticulum (ER) protein. Biosynthetic labeling and temperature block studies of A tT-20 cells demonstrated the localization of RESP18 to the ER lumen by a unique mechanism, degradation by proteolysis in a post-ER pre-Golgi compartment, Proteases in this compartment were saturated by exogenou s RESP18 overexpression in AtT-20 cells. Furthermore, a calpain protea se inhibitor enhanced secretion of RESP18 from AtT-20 cells overexpres sing RESP18, Saturation and inhibition of the RESP18 degrading proteas es allowed RESP18 to enter secretory granules and acquire a post-trans lational modification, likely O-glycosylation; this modified 21-kDa RE SP18 isoform was the only RESP18 secreted. Rat anterior pituitary extr acts contain 18-kDa and O-glycosylated RESP18 with similar properties. Exogenous RESP18 expression in hEK-293 cells demonstrated ER localiza tion and RESP18 metabolism similar to AtT-20 cells, indicating that th e cellular machinery involved in localizing RESP18 is not specific to neuroendocrine cells. The data implicate a novel ER localization mecha nism for this neuroendocrine-specific luminal ER resident.