Abstract
Renal cell carcinoma (RCC) accounts for 2% of all adult malignancies and is the most lethal of common urologic cancers. The major type of RCC is clear cell RCC (ccRCC). It is highly resistant to traditional therapies, and surgery remains to be the main method of treatment. Therefore, identification of RCC-associated genes is important in understanding the molecular mechanisms of ccRCC. In previous studies, full-length enriched cDNA libraries of ccRCC and normal kidney tissues were constructed by Mr. Sai-Wen Tang from this laboratory. By comparing the differential gene-expression profiles of ccRCC and normal tissues, Heme oxygenase 1 (HO-1) and Annexin A2 (AnxA2) were found to be up-reglulated in ccRCC tissues. AnxA2 is a Ca2+-dependent phospholipid binding protein, and its overexpression has been found in virally transformed cell lines and various tumors. HO-1 is a heat shock protein induced by a variety of stress stimuli. HO-1 catalyzes the degradation of heme to produce CO, biliverdin, and Fe2+. Elevated HO-1 expression was found in various tumors and linked to angiogenesis in some tumors. These findings suggest that HO-1 and AnxA2 might play a crucial role in tumor development and progression. In present study, the expression of HO-1 and AnxA2 genes were found up-regulated in mRNA as well as protein levels of ccRCC tissue pairs. Immunohistochemical studies showed that HO-1 localized in the nucleus in ccRCC tissues, and this was further confirmed in kideney and RCC cell lines by confocal microscopy and subcellular fractionation. Therefore, yeast two-hybrid was performed to identify HO-1 interacting proteins in the nucleus. By functional studies, we have demonstrated that overexpression of HO-1 in HEK293 cell line induced the up-regulation of several G1/S cell cycle regulatory genes, and it also protected cells from cisplatin induced apoptosis and up-regulated protein levels of bcl-2. Taken together, it is suggested that overexpression of HO-1 in ccRCC could provide a selective advantage towards cell transformation, and protect cells from cisplatin- induced apoptosis. Furthermore, the identification of putative HO-1 binding proteins by yeast two-hybrid suggested that HO-1 might participate in cell signaling in the nucleus and also the activation of the NFκB pathway.
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