title: Inhibition of Src activity enhances the tumor-suppressive effect of the connexin 32 gene in Caki-1 renal cancer cells.
abstract: Connexin (Cx) genes exert negative growth effects on tumor cells with certain cell specificity. We have recently reported that Cx32 acts as a tumor suppressor gene in a metastatic renal cancer cell line (Caki-1) due to the inactivation of Src. In line with the previous study, here we investigated if an Src family inhibitor (PP1) could enhance the tumor-suppressive effect of Cx32 in Caki-1 cells from human metastatic renal cell carcinoma. We examined the difference in the cytotoxic effect of PP1 on two cell clones, Cx32-transfected Caki-1 cells (Caki-1T) and mock-transfected Caki-1 cells (Caki-1W), in vitro as well as in vivo. PP1 showed more cytotoxic effect on Caki-1T than on Caki-1W at lower doses. This reinforcement was also observed in a xenograft model of nude mice. The in vitro reinforcement of the cytotoxic effect depended not only on control of cell-cycle transition but also on the induction of apoptosis, and the occurrence of the event was mostly caused by potential inhibition of Src activity in Caki-1T. Also, under a hypoxic condition, which is a typical environment of tumor tissue, Cx32 suppressed hypoxia-induced Src activation, and PP1 enhanced cytotoxicity in Caki-1T. These results suggest that, in addition to the Cx32-dependent tumor-suppressive effect, the concomitant inhibition of Src by PP1 is an effective procedure to induce a cytotoxic effect in Caki-1 cells.
authors.affiliation: Department of Food Science Research for Health, National Institute of Health and Nutrition, Toyama, Tokyo 162-8636, Japan.
authors.forename: Eriko
authors.initials: E
authors.lastname: Fujimoto
authors.forename: Hiromi
authors.initials: H
authors.lastname: Sato
authors.forename: Sumiko
authors.initials: S
authors.lastname: Shirai
authors.forename: Yoji
authors.initials: Y
authors.lastname: Nagashima
authors.forename: Nantiga
authors.initials: N
authors.lastname: Virgona
authors.forename: Kiyokazu
authors.initials: K
authors.lastname: Hagiwara
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamasaki
authors.forename: Etsuko
authors.initials: E
authors.lastname: Negishi
authors.forename: Koichi
authors.initials: K
authors.lastname: Ueno
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Yano
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002292:Carcinoma, Renal Cell / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects; D015687:Cell Hypoxia; D017630:Connexins / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000627:therapeutic use*; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011720:Pyrazoles / Q000627:therapeutic use*; D011743:Pyrimidines / Q000627:therapeutic use*; D014162:Transfection; D014407:Tumor Cells, Cultured; D000097002:Gap Junction beta-1 Protein
chemical_list: D017630:Connexins; D004791:Enzyme Inhibitors; D016392:Proto-Oncogene Proteins pp60(c-src); D011720:Pyrazoles; D011743:Pyrimidines; D000097002:Gap Junction beta-1 Protein; C108123:4-amino-5-(4-methylphenyl)-7-(tert-butyl)pyrazolo(3,4-d)pyrimidine