TISSUE-SPECIFIC AND SUBSTRATE-SPECIFIC ENDOPROTEOLYTIC CLEAVAGE OF MONKEY PROOPIOMELANOCORTIN IN HETEROLOGOUS ENDOCRINE-CELLS - PROCESSING AT LYS-LYS DIBASIC PAIRS
Hl. Lin et al., TISSUE-SPECIFIC AND SUBSTRATE-SPECIFIC ENDOPROTEOLYTIC CLEAVAGE OF MONKEY PROOPIOMELANOCORTIN IN HETEROLOGOUS ENDOCRINE-CELLS - PROCESSING AT LYS-LYS DIBASIC PAIRS, Neuroendocrinology, 58(1), 1993, pp. 94-105
This study compares the processing of pro-opiomelanocortin (POMC) at t
wo Lys-Lys cleavage sites, located in the carboxy-terminal domain of t
he precursor; one site marking the amino terminus of beta-melanocyte-s
timulating hormone (beta-MSH) and the other in the carboxy-terminus of
beta-endorphin (betaE), These comparisons were carried out by transfe
cting monkey POMC cDNA into two heterologous cell lines: AtT-20, which
endogenously expresses mouse POMC, and Rin m5F, which has been previo
usly used as a host for transfected POMC. These cells lines are known
to process POMC differently at Lys-Arg residues, though less is known
about their Lys-Lys cleavage. Our results have demonstrated both tissu
e-specific and site-specific factors controlling Lys-Lys cleavage. The
AtT-20 line appears not to perform either Lys-Lys cleavage. Rin m5F c
ells, on the other hand, fail to process the site at the carboxy termi
nus of betaE (betaE28-29) but do process, to a significant extent, the
N-terminal site to beta-MSH. That this differential processing is unl
ikely to be due to a POMC conformation which would make the betaE site
inaccessible was demonstrated by mutating the sites from Lys-Lys to L
ys-Arg. With such mutants, Rin m5F cells fully processed at both locat
ions. Interestingly, the mutant Lys-Arg sites were not fully processed
by AtT-20 cells. These results are discussed in terms of the compleme
nt of processing enzymes expressed in each of the cell lines, as well
as the role of residues surrounding the diabasic cleavage sites in det
ermining the likelihood of proteolysis.