The role of GJIC in tumors is not entirely clear: on the one hand there are several tumors which do not express any connexin, e.g., HeLa cells (King et al., 2000a), and while many tumor promoting agents down regulate GJIC (Salameh and Dhein, 2005), and while tumor oncogenes like ras, src, raf, and mos have been shown to downregulate GJIC (Trosko et al., 2004). This evidence concerns the gene MOS and neoplasm.