Table 1.

Possible mechanisms responsible for reduced expression of connexins in human cancers and cell lines.

Protein	Tumor	Alteration
Cx26	Squamous cell carcinoma oral cavity	Missense heterozygous single nucleotide mutation F142L (Rednam et al., 2011)
	Transitional carcinoma cell lines	Histone demethylation (Li et al., 2013)
	Small cell carcinoma (SCLC) and SCLC cell lines	Promoter hypermethylation (Chen et al., 2005)
	Invasive breast carcinoma (IBC) and IBC cell lines	Promoter hypermethylation (Tan et al., 2002)
Cx30	Colorectal carcinoma (CRC) and CRC cell lines	Promoter hypermethylation (Sirnes et al., 2011)
Cx32	Renal cell carcinoma cell lines	Promoter hypermethylation (Hirai et al., 2003)
	Gastric carcinoma	Promoter hypermethylation (Schalper et al., 2014, this report)
Cx36	Colorectal carcinoma (CRC) and CRC cell lines	Promoter hypermethylation (Sirnes et al., 2011)
Cx37	Colorectal carcinoma	Promoter hypermethylation (Sirnes et al., 2011)
	Hepatic angiosarcoma	High frequency of codon 319 polymorphism in vinyl chloride-related tumors (Saito et al., 2000)
Cx40.1	Hepatocellular carcinoma	Deletion (Zender et al., 2008)
Cx43	Colorectal carcinoma	Single nucleotide deletion A311V, Single nucleotide insertion I358N (Dubina et al., 2002)
	Non-small cell lung carcinoma	Promoter hypermethylation (Jinn and Inase, 2010)
	Prostate carcinoma cell lines	Histone deacetylation (Hernandez et al., 2006), miR-20a expression is inversely correlated with Cx43 expression (Li et al., 2012a,b)
	Glioblastoma multiforme cell line	miR-221/222 targets Cx43 mRNA, decreasing its expression (Hao et al., 2012)
	Nasopharyngeal carcinoma (NPC) and NPC cell line	miR-218 targets Cx43 mRNA and is downregulated in NPC (Alajez et al., 2011)
Cx45	Colorectal cancer cell lines	Promoter hypermethylation (Sirnes et al., 2011)
Cx62	Prostate carcinoma	6q14-21 deletion (Liu et al., 2007)