Induction of haptoglobin by all-trans retinoic acid in THP-1 human monocytic cell line

Haptoglobin (Hp) is one of the acute-phase proteins and is mainly synthesiz ed in the liver. During our study on the differentiation of leukemia cells, we have found that Hp is synthesized in human monocytic cells by all-trans retinoic acid (ATRA). The synthesis of Hp by ATRA is induced in a dose- an d time-dependent manner, Hp cDNA cloned from ATRA-treated THP-1 cells corre sponds to the Hp alpha2(FS)-beta form. Whereas ATRA acted as a strong induc er in THP-1 cells, IL-1 beta, TNF-alpha, IL-6, and LPS had little effect on Hp gene expression in these cells, These findings suggest that THP-1 cells express the Hp gene through a signal pathway different from hepatocytes, a nd that ATRA is a potent Hp-inducer in these cells. (C) zool Academic Press .