OVEREXPRESSION OF THE HEME OXYGENASE GENE IN RENAL-CELL CARCINOMA

Heme oxygenase (HO) activity has been implicated in the regulation of renal function and cell growth in normal and disease states. Expressio n of HO genes has been shown to regulate important hemoprotein(s) such as cytochrome P450. In the present study, HO activity was measured in samples of human adenocarcinoma, juxtatumor, and normal renal tissues . The samples were histologically examined to verify the malignant and normal nature. HO activity was 4-fold higher in the adenocarcinoma th an in either normal or juxtatumor tissues. We designed a reverse trans criptase-polymerase chain reaction (RT-PCR) method to assess the prese nce of HO-1 and HO-2 mRNA in biopsy samples of various human renal tis sues. Total RNA from renal samples was reverse transcribed and amplifi ed simultaneously by PCR using specific primers for HO-1 and HO-2. Res ults show that both HO-1 and HO-2 mRNAs were expressed in all renal ti ssues examined and that HO-1 appeared to be amplified more than HO-2. Northern blot analysis revealed that HO-1 mRNA was elevated by several fold in adenocarcinoma compared with juxtatumor or normal tissues. In contrast, no differences in HO-2 mRNA levels were observed using eithe r RT-PCR or Northern blot. Cytochrome P450 arachidonic acid epoxygenas e and omega-hydroxylase activities were markedly reduced in the tumor tissues, whereas, in the juxtatumor tissue, cytochrome P450 omega-hydr oxylase activity was significantly increased. Northern blot analysis u sing cytochrome P450 cDNA probe 4A2 cDNA for the omega-hydroxylase gen e family revealed that mRNA levels for omega-hydroxylase transcripts w ere significantly decreased in the adenocarcinoma compared with juxtat umor. The decrease in cytochrome P450 4All mRNA levels correlated with a decrease in the arachidonic acid omega-hydroxylation metabolite, 20 -HETE. The production of 20-HETE was significantly higher in juxtatumo r in agreement with omega-hydroxylase mRNA. Higher levels of HO-I may be a contributing factor for the undetectable levels of cytochrome P45 0 arachidonic acid metabolites, 20-HETE, in the adenocarcinoma. Our re sults suggest that increased generation of mitogenic activities by ome ga-hydroxylase and 20-HETE in the juxtatumor may be a contributing fac tor in the development and growth of neoplastic tissues, and the induc tion of HO in the tumor tissue may be an attempt to limit oxidative in jury caused by the cytochrome P450 metabolites and other oxidative str ess.