GJA1 and infection: Notable among the down-regulated proteins that are at least 50% lower than normal expression in the absence of infection are: The gap junction a-1 protein (Gja1), also called the major gap junction protein Connexin 43 (Cx43), is a contractility-associated protein that is markedly enhanced in response to estrogen in the reproductive tract epithelial stromal cells and the embryo during the early phases of pregnancy.