title: Induction of the connexin 32 gene by epigallocatechin-3-gallate potentiates vinblastine-induced cytotoxicity in human renal carcinoma cells.
abstract: OBJECTIVE
  Enforced expression of the connexin (Cx) 32 gene, a member of the gap junction gene family and a tumor suppressor gene in human renal cell carcinoma (RCC), enhanced vinblastine (VBL)-induced cytotoxicity in RCC cells due to suppression of multidrug resistance 1 (MDR1) expression. Furthermore, in RCC the Cx32 gene is silenced by hypermethylation of CpG islands in a promoter region of the Cx gene. In this study, we investigated if the green tea polyphenol epigallocatechin-3-gallate (EGCG) could enhance susceptibility of RCC cells (Caki-1, a human metastatic RCC cell) to VBL.
  
  
  METHODS
  The effects of EGCG on Caki-1 cells were estimated by WST-1 (cell viability), real-time RT-PCR (mRNA level) and immunoblotting (protein level). We estimated the methylation status in the promoter region of the Cx32 gene in RCC cells by methylation-specific PCR. Each protein function was inhibited by small interfering RNA (siRNA) and specific inhibitors.
  
  
  RESULTS
  The EGCG treatment elicited significant upregulation of Cx32 in Caki-1 cells, and the induction of the Cx led to the suppression of MDR1 mRNA expression through inactivation of Src and subsequent activation of c-Jun NH2-terminal kinase (JNK). Chemical sensitivity to VBL in Caki-1 cells was increased by EGCG pretreatment, and this effect was abrogated by siRNA-mediated knockdown of Cx32.
  
  
  CONCLUSIONS
  This study suggests that the restoration of Cx32 by EGCG pretreatment improves chemical tolerance on VBL in Caki-1 cells via the inactivation of Src and the activation of JNK.
authors: Research Group on Nutritional Sciences, Faculty of Life Sciences, Toyo University, Itakura, Japan.
authors: Ayami
authors: A
authors: Sato
authors: Miki
authors: M
authors: Sekine
authors: Minako
authors: M
authors: Kobayashi
authors: Nantiga
authors: N
authors: Virgona
authors: Masako
authors: M
authors: Ota
authors: Tomohiro
authors: T
authors: Yano
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism; D002292:Carcinoma, Renal Cell / Q000378:metabolism / Q000473:pathology; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects*; D017630:Connexins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D019175:DNA Methylation; D006801:Humans; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects; D014747:Vinblastine / Q000633:toxicity*; D000097002:Gap Junction beta-1 Protein
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002392:Catechin; D017630:Connexins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D014747:Vinblastine; D000097002:Gap Junction beta-1 Protein; C045651:epigallocatechin gallate