Regulation of growth factor receptors by klotho in human renal cell carcinoma

Abstract

Background: Klotho has been known to be an aging-suppressor gene and predominantly expressed in renal tubules. Some studies revealed that Klotho expression was related to favorable behavior of melanoma, renal cell carcinoma, breast, and lung cancers. In addition, it has been reported that Klotho is a tumor suppressor and modulator of growth factor receptors (GFRs) signaling in human breast cancer. Clear cell renal cell carcinoma (CCRCC) is the most common kidney malignancy, originating from renal tubules, which are the source of Klotho. However, expression and function of Klotho in the xv tumorigenesis of renal cancer remain elusive. Therefore, we examined the expression of Klotho and GFRs in CCRCC and validated their prognostic significance. Furthermore, we investigated the molecular mechanism explaining the relationship between Klotho and GFRs in the tumorigenesis of CCRCC. Materials and methods: Immunohistochemical (IHC) staining for Klotho and GFRs was performed on 126 formalin-fixed paraffin-embedded CCRCC tissue samples. Western blot analysis was used to check the expression of Klotho, insulin receptor (IR), insulin-like growth factor (IGF-1) receptor (IGF-1R), and vascular endothelial growth factor receptor (VEGFR)-1 in 18 fresh tissues of these cases. We also examined phosphorylation of insulin, IGF-1, epidermal growth factor (EGF), and platelet-derived growth factor (PDGF) induced downstream pathways before and after treatment of Klotho in two clear cell renal cell carcinoma cell lines (ACHN and Caki1). The results were compared with various clinico-pathological prognostic factors of CCRCC and with patient survival. Results: Higher Klotho expression was significantly correlated with favorable prognostic factors of CCRCC. Klotho positive patients had significantly better survival than Klotho negative patients. Among the GFRs, higher expression of IR and VEGFR-1 were related to favorable prognostic factors of CCRCC. In contrast, higher expression of IGF-1R and EGFR xvi correlated with unfavorable prognostic factors of CCRCC. Interestingly, Klotho inhibited IGF-1- and EGF-induced AKT activation in CCRCC cell lines. Conclusion: Klotho inhibition of IGF-1 and EGF pathways suggests that Klotho might be a potential tumor suppressor in CCRCC. Therefore, Klotho is critical for the development of CCRCC and is valuable for therapeutic target of CCRCC.