CONCURRENT UPREGULATION OF HAEM OXYGENASE 1 AND CYTOCHROME P450 2A5: POSSIBLE ROLE OF Nrf2 AND hnRNP A1

Michael R. Moore1, Aedah A. Bakar1, Matti A Lang2

1EnTox, The University of Queensland, Australia, 2Department of Biochemistry, Uppsala University, Sweden

We have been investigating the molecular mechanisms by which cadmium (Cd) affects the regulation of cytochrome P450 2A5 (CYP2A5) and haem oxygenase 1 (HO-1). CdCl2 treatment (16 mmol/kg body weight) in DBA/2J male mice resulted in significant (P<0.05) progressive decrease of total hepatic cytochrome P450 (CYP450) content as well as significant increase of haem oxygenase activity with time. In contrast, a late effect of the treatment showed progressive increase in coumarin 7-hydroxylase activity (catalysed by CYP2A5). Northern blot analysis suggests that the treatment concurrently induced expression of HO-1 and CY2A5 mRNAs with the expression of the former precedes that of the latter.

Western blot analysis and UV cross-linked assay using cytoplasmic and nuclear protein extracts from the liver of treated mice suggests that the treatment causes translocation of heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) from the nucleus to the cytoplasm. Western blot analysis also showed that Nrf2 is translocated from the cytoplasm to the nucleus. The translocations of both hnRNP A1 and Nrf2 were observed at a time range corresponds to the progressive increase of HO-1 and CYP2A5 mRNA expression.

The pattern of concurrent induction of HO-1 and CYP2A5 by Cd suggests that the transcription factor, Nrf2 and the multifunctional protein hnRNP A1 may be involved in the up-regulation. To date, we have been unable to establish whether or not the  proteins interact with each other in synchronising the transcription and post-transcription regulation of both enzymes.