Distinct Regulations of Gene Expression for Stress Response and Substrate Induction.

Heme oxygenase 1 (HO-1) is the key enzyme for heme catabolism and cytoprotection. Whereas gene expression in response to various stresses has been investigated extensively, the precise mechanisms by which gene expression is regulated by the HO-1 substrate heme remain elusive. To systematically examine whether stress-mediated induction and substrate-mediated induction of utilize similar or distinct regulatory pathways, we developed an HO-1-DsRed-knock-in reporter mouse in which the gene is floxed by loxP sites and the gene has been inserted. Myeloid lineage-specific recombination of the floxed locus led to fluorescence derived from expression of the HO-1-DsRed fusion protein in peritoneal macrophages. We also challenged general recombination of the locus and generated mice harboring heterozygous recombinant alleles, which enabled us to monitor HO-1-DsRed expression in the whole body and . HO-1 inducers upregulated HO-1-DsRed expression in myeloid lineage cells isolated from the mice. Notably, analyses of peritoneal macrophages from HO-1-DsRed mice lacking NRF2, a major regulator of the oxidative/electrophilic stress response, led us to identify NRF2-dependent stress response-mediated induction and NRF2-independent substrate-mediated induction. Thus, the gene is subjected to at least two distinct levels of regulation, and the available lines of evidence suggest that substrate induction in peritoneal macrophages is independent of CNC family-based regulation.