Expression of prohormone processing enzymes in neuroendocrine and non-neuroendocrine cells

The biosynthesis of many peptides thought to have autocrine or paracrine effects on cell growth requires a series of enzymatic steps. The level of expression of two of these posttranslational processing enzymes was compared in several endocrine and non-neuroendocrine cell lines. Peptidylglycine alpha-amidating monooxygenase (PAM; EC 1.14.17.3) is a bifunctional copper- and ascorbate-dependent enzyme essential in the formation of alpha-amidated peptides. Carboxypeptidase H (CPH; EC 3.4.17.10) removes basic residues from the carboxyterminus of the products of endoproteolytic cleavage of prohormones and is generally essential in the formation of substrates for PAM. PAM messenger RNA (mRNA) and activity were detectable in both endocrine (AtT-20, GH3) and non-neuroendocrine (L, 3T3, COS, BRL, C127) cells. Except for BRL cells, CPH mRNA and enzymatic activity were detectable in all the cell lines. BRL cells contained no detectable CPH mRNA and had a different carboxypeptidase B-like activity. Thus, expression of secretory granule-associated processing enzymes is not limited to cells of a classic neuroendocrine phenotype.