GJB2 and melanoma: Tumor heterogeneity was also reflected by the differential Cx expression among the three invasive, metastatic melanoma cell lines, which altogether involved seven detectable isotypes (GJA1/Cx43, GJB1/Cx32, GJB2/Cx26, GJA3/Cx46, GJB3/Cx31, GJC1/Cx45, GJD3/Cx30.2) at mRNA and four (no Cx43 and unreliable Cx31 and Cx45), at protein level.