The antitumoral effects of HO-1 in colorectal cancer are dependent on the presence of a wild type p53

Abstract

Previously, we reported that heme oxygenase-1 (HO-1) is associated with increased overall survival time of patients with invasive colorectal cancer (CRC) and that HO-1 activation de- creases the viability of human CRC cell lines that carry a wild- type p53 although it has no effect on cells with absent/mutated p53. The hypothesis of this work is that p53 might be involved in the antitumoral effect of HO-1 in CRC. By using a xenograft of p53 wild type-containing HCT116, we first demonstrated that genetic overexpression of HO-1 delayed tumor growth (p<0.05) and decreased tumor volume and weight (p<0.01) compared to controls. Also, p53 was upregulated in HO-1-overexpressing cells (p<0.05). We then evaluated the effects of pharmacologic activa- tion of HO-1 (hemin) in HCT116 p53wt or HCT116 p53-/- xenograft tumors. Hemin (H) treatment delayed tumor growth (p<0.01) and decreased tumor volume (H=740.6 vs C=3082 mm3; p<0.01) and weight (H=0.8 vs C=3.2 g; p<0.05) only in HCT116 p53wt tumors, although it increased HO-1 levels in both tumor types (p<0.01). In support of these results, in silico studies showed a trend towards higher overall survival in CRC patients with high HO-1 and p53wt compared to those with low HO-1 or mutated p53. To start investigating p53 regulation by HO-1, we performed HO-1 chromatin immunoprecipitation assays and found that HO-1 does not bind to p53 promoter. In addition to affecting cell viabil- ity, genetic and pharmacological modulation of HO-1 decreased cell migration (p<0.05) and invasion (p<0.001) only in HCT116 cells, not affecting these processes in HCT116 p53-/- cells. These effects were accompanied by E-cadherin upregulation (p<0.05). In concordance, preliminary results obtained in human CRC biopsies by immunohistochemistry, showed a positive cor- relation between HO-1 and E-cadherin (p<0.01). In conclusion, our data demonstrate an antitumoral role for HO-1 in CRC and show evidence of the importance of a wild type p53 for this role