GJA1 and breast cancer: In addition, this study showed that mice with an osteocyte-specific genetic knockout of Cx43, or transgenic mice engineered to have osteocyte-specific expression of a Cx43 mutant (∆130–136) without functional GJ or hemichannels, exhibited enhanced tumor growth of transplanted mammary tumor cells, but not when a GJ-deficient and functional hemichannel Cx43 mutant (R76W) was expressed in osteocytes.