Expression of PC3, carboxypeptidase E and enkephalin in human monocyte-derived macrophages as a tool for genetic studies.

Circulating monocytes in human peripheral blood are readily available, easily obtained, and can be cultured in vitro. Once plated, the monocytes spontaneously differentiate into macrophages. Undifferentiated human monocytes do not express carboxypeptidase E (CPE), prohormone convertase 3 (PC3/PC1) or proenkephalin (ENK), suggesting that gene induction during differentiation results in the expression of these genes. RT-PCR of human monocyte-derived macrophage (HMDM) mRNA showed detectable levels of ENK mRNA at 48 h after plating, followed by PC3 and CPE mRNAs at 72 h. PC3 expression was confirmed by Western blotting in THP-1 cells. Similarities in expression of enzymes involved in the conversion of neuroendocrine precursors, such as proenkephalin, into functionally mature peptides underscores the close association HMDMs may share with the neuroendocrine system. Because of this, HMDMs may prove to be a valuable, non-surgical source of human tissue for clinical genetic diagnosis of some convertase disorders.