Decreased expression of REIC/Dkk-3 in human renal clear cell carcinoma

Purpose: We examined the expression of REIC/Dkk-3, a possible candidate for a tumor suppressor gene, in human renal clear cell carcinoma (RCCC) cell lines and sporadic RCCC surgical specimens. Materials and Methods: Human RCCC cell lines (Caki-1, Caki-2, ACHN and KPK-1) and several control cell lines were used to examine the expression of REIC/Dkk-3 mRNA and characterize a newly raised antibody specific for REIC/Dkk-3 protein. Pairs of cancerous and adjacent noncancerous tissues were obtained from 20 patients with RCCC. Of them 17 and 7 cases were analyzed by real-time quantitative reverse transcriptase-polymerase chain reaction, and by Western blot analysis and/or immunohistochemical analysis, respectively. Results: The decreased expression of REIC/Dkk-3 mRNA and protein in human RCCC cell lines, and the specificity of the new antibody were confirmed. In a real-time quantitative reverse transcriptase-polymerase chain reaction study using 17 pairs of RCCC and adjacent normal tissues REIC/Dkk-3 mRNA levels were significantly decreased in carcinoma tissues (by 25% to approximately 95% in 15 pairs). Western blot analysis and immunohistochemistry revealed a significant decrease in REIC/Dkk-3 protein levels in 6 of the 7 and 13 of the 14 RCCC cases analyzed, respectively. Conclusions: The decrease in REIC/Dkk-3 mRNA and protein levels was observed irrespective of tumor grade and stage, indicating the involvement of REIC/Dkk-3 in an initial step of malignant conversion. Consequently REIC/Dkk-3 could be a new molecular target for therapeutic measures against RCCC.