Table 2: The connexins and their expression, localization, and function in normal breast and breast tumor.

Connexin⁢Normal breast⁢Breast tumor
ExpressionFunctionExpressionFunction

Cx26Luminal epithelial cells Luminal cell proliferation
Production of milk
Downregulated in primary tumor
Upregulated in metastatic tissue
Cx43Myoepithelial cells
Decreased during mid-pregnancy and lactation
Proper production and ejection of milk Downregulated in primary tumor
Upregulated in metastatic tissue
Increases invasion, adhesion of tumor cells
Cx30Mouse luminal epithelial cells
Peak expression at the onset of lactation
Lactation
Compensates for impaired Cx32
Cx32Mouse luminal epithelial cells
Increased expression at parturition
Production of milk
Compensates for impaired Cx30 function
Increased expression at metastatic lymph node
Cx46 Expression not reported in mouse or human normal breastExpressed in primary tumor May protect tumor cells from hypoxia induced death