Heme oxygenase-1 (HO-1) is an antioxidant, antiapoptotic and cytoprotective enzyme, catalysing the degradation
of heme to carbon monoxide, biliverdin and ferrous iron. Recent studies indicated that expression of HO-1 is under
the control of proapoptotic transcription factor p53 and antioxidant transcription factor Nrf2. Whether each of these transcription
factors act independently or there is a cooperation between them in inducing HO-1 expression remains to be elucidated.
In this study, we examined the expression of HO-1 in B16F10 melanoma and 4T1 breast cancer cells after cell
exposure to proteasome inhibitors. We found that HO-1 protein level is increased by about 70% in p53-wt B16F10 cells in
response to proteasome inhibitor MG132 after 6 h. Likewise, a 6.8 fold increase in HO-1 level was observed after cell exposure
to the highly specific proteasome inhibitor bortezomib after 6 h of treatment in B16F10 cells. Whereas no induction
of HO-1 was observed in p53-null 4T1 cells after treatment with bortezomib for 6 h. Next, we aligned HO-1 untranslated
region with a consensus p53-responsive element. This bioinformatic analysis identified a p53-responsive element
within the untranslated region of HO-1. Then, we examined HO-1 expression after a prolonged exposure to bortezomib in
both B16F10 and 4T1 cell. These analyses similarly indicated that HO-1 is strongly induced in B16F10 cells in a dosedependent;
contrary to our expectations, a strong induction of HO-1 is also observed in 4T1 cells. Therefore, it is concluded
that HO-1 expression is under the control of p53 during early time points of proteasomal inhibition. However, during
prolonged incubation with proteasome inhibitors, HO-1 expression can be induced in a p53-independent manner, suggesting
participation of other protein(s) with longer half-lives.
Keywords: Bortezomib, B16F10, cancer, HO-1, p53, 4T1, antioxidant, cytoprotective enzyme, biliverdin, proapoptotic transcription factor p53.
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