Nc. Day et al., CHARACTERIZATION OF PROOPIOMELANOCORTIN PROCESSING IN HETEROLOGOUS NEURONAL CELLS THAT EXPRESS PC2 MESSENGER-RNA, Neuropeptides, 24(5), 1993, pp. 253-262
We have investigated processing of monkey pro-opiomelanocortin (POMC)
following transfection into heterologous neuronal Neuro 2A (N2A) cells
. In several separately transfected stable cell lines (termed N2A/POMC
2-like; n = 4), POMC was processed to betaE only, by direct cleavage f
rom the precursor. Thus, these cell lines did not produce betaE in the
orderly manner observed in the pituitary, that is, via the intermedia
te peptide betaLPH. Analysis of one representative N2A/POMC2 cell line
revealed that the extent of processing to betaE appeared to be negati
vely correlated with precursor expression level, suggesting that the p
rocessing enzyme(s) in these cells was present in limiting amounts. No
rthern analysis of PC1 and PC2, two recently cloned processing enzymes
, showed that N2A/POMC2 cells expressed low levels of PC2 mRNA, but no
detectable PC1 mRNA. These data suggest that (1) the order of process
ing observed in the pituitary is not exclusively determined by tertiar
y folding of the precursor, but rather by the complement of processing
enzymes in a particular cell, and (2) if PC2 is responsible for POMC
processing in N2A/POMC2 cells, this enzyme, expressed in limiting amou
nts, appeared to show selectivity for the betaE amino terminal process
ing site.