EMMPRIN (basigin/CD147) expression is not correlated with MMP activity during adult mouse mammary gland development

Extracellular matrix metalloproteinase inducer (EMMPRIN/basigin/CD147) is a cell surface protein, which has been associated with the induction of matrix metalloproteinase (MMP) genes during cancer metastasis. EMMPRIN plays a role in a variety of physiological processes as is evident by the diverse deficiencies detectable in EMMPRIN knockout mice. We have analysed the role of EMMPRIN in the induction of MMP genes during mammary gland differentiation and involution. Co-transfection studies showed that EMMPRIN has diverse effects on MMP promoter activity in different mammary and non-mammary cell lines. Expression of EMMPRIN mRNA is enhanced markedly by insulin in a mammary gland cell line but appears to have no direct effect on MMP gene expression in these cells. Microarray analysis and quantitative PCR show that EMMPRIN is expressed throughout mammary gland differentiation in the mouse. Its expression decreases during early pregnancy and briefly after induction of mammary gland involution by litter removal. Immunohistochemical analysis shows that EMMPRIN expression is limited to the stromal compartment during pregnancy, whereas it is strongly expressed in the epithelium during lactation. In summary the data argue against a causal role for EMMPRIN for the induction of MMP gene expression during adult mammary gland development. These data therefore support a physiological role for EMMPRIN other than MMP induction in mammary gland biology.