PROCORTICOTROPHIN-RELEASING HORMONE - ENDOPROTEOLYTIC PROCESSING AND DIFFERENTIAL RELEASE OF ITS DERIVED PEPTIDES WITHIN ATT20 CELLS

Procorticotrophin-releasing hormone (proCRH) is expressed mainly in th e hypothalamus and in the placenta, where it undergoes tissue-specific endoproteolysis. Our results show that within stably transfected AtT2 0/D16V cells proCRH is cleaved to generate two fragments of approximat e to 8 and 3 kDa which could account for proCRH(125-194) and proCRH(12 5-151), respectively, and a 4.5 kDa product which could account for ma ture IR-CRH(1-41). The immunofluorescence staining patterns for IR-CRH and IR-ACTH and their response of secretagogues indicate targeting of proCRH and POMC to the secretory pathway in transfected AtT20 cells. In this work, we have used a unique set of specific RIAs and IRMAs to the full length POMC and proCRH molecules and several products of endo proteolytic processing to assess if they could be released differentia lly in response to stimulation. Although the release of both IR-ACTH a nd IR-CRH peptides from transfected AtT20 cells is stimulated in respo nse to exposure to high potassium stimulation (51 mM KCl/5mM CaCl2), t he sorting index(SI) suggests that mature ACTH is sorted to the regula ted secretory pathway 2.1-fold more efficiently than mature CRH(1-41). Mature ACTH is also sorted to the regulated secretory pathway 9-fold more efficiently than IR-proCRH(125-151), Also, mature CRH(1-41) is so rted to the regulated secretory pathway 3-fold more efficiently than I R-proCRH(125-151). These results therefore indicate that the intracell ular mechanisms for the storage and release of POMC, proCRH and their endoproteolytic products differ and would sustain the hypothesis that within mammalian peptidergic cells, different biologically active pept ides originating from the same or different precursor molecules: could be differentially released in response to specific stimuli. This woul d give these cells the capacity to finely regulate neurotransmitter re lease in response to environmental and physiological demands. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.