REGULATION OF EXPRESSION OF THE HUMAN HEME OXYGENASE-1 GENE IN TRANSFECTED CHICK-EMBRYO LIVER-CELL CULTURES

Induction of heme oxygenase (HO) has been proposed as a protective cel lular mechanism against oxidative damage. In previous work (Tyrrell et al., Carcinogenesis [1993] 14, 761-765), portions of the 5' promoter region of the human HO-1 gene linked to the reporter gene chlorampheni col acetyl transferase (CAT), had been transiently expressed in HeLa c ells, To extend the study of human HO gene expression into primary liv er cells, these reporter gene fusion constructs, containing 121 or 141 6 base pairs of the untranscribed 5'-upstream sequences of the human H O-1 gene, were used along with pSV beta-Gal plasmid to dually transfec t primary cultures of chick embryo liver cells (CELC). The transfected cells were treated with selected metals, heme, phorbol ester, and che mical agents that produce oxidative stress (H2O2 or sodium arsenite). Reporter gene activities were measured 18-20 h later, Our major findin gs are: (1) these HO-CAT constructs were expressed in CELC; (2) unlike HeLa cells, the expression of CAT was detected in CELC without the ne ed for the SV40 enhancer; (3) sodium arsenite and cobalt chloride indu ced the expression of the HO-CAT constructs whereas heme had no effect on or decreased CAT expression for all of the transfected constructs; (4) study of endogenous chick HO-1 gene expression in CELC showed tha t HO-1 responded to sodium arsenite treatment in a dose-dependent fash ion, and the response was rapid and transient. We conclude that, in ch ick liver cell cultures, induction of the HO-1 gene by heme is fundame ntally different from that produced by transition metals or sodium ars enite. Furthermore, the results suggest that expression of the HO-1 ge ne is highly conserved across species. (C) 1997 Elsevier Science B.V. All rights reserved. (C) 1997 Elsevier Science B.V.