Regulation of Sialomucin Complex Expression and Its Affect on Her Receptor Interaction (96 Breast)

Abstract : Sialomucin complex (SMC) is a heterodimeric glycoprotein complex consisting of a mucin subunit ASGP-1 (ascites sialoglycoprotein-1) and a transmembrane subunit, ASGP-2, which can act a S a ligand for the receptor tyrosine kinase ErbB2. SMC is a highly expressed protein on the surface of ascites 13762 rat mammary adenocarcinoma cells, approximately 10 to the 2nd power times the level in lactating mammary gland and 10 to the 4th power times that in virgin mammary gland. SMC is largely post transcriptionally regulated in developing mammary gland. Additionally, SMC can be post transcriptionally in normal cultured rat mammary epithelial cells (MEC) but nor 13762 MAT-B1 mammary tumor cells by Matrigel by inhibition of SMC precursor synthesis. SMC is also post translationally regulated by TGF beta in cultured normal MEC by inhibition of SMC precursor processing into mature ASGP-1 and ASGP-2. Interestingly, SMC levels in 13762 MAT-B1 tumor cells are unaffected by TGF beta. SMC and ErbB-2 have similar expression patterns in normal developing mammary gland and can be found in a complex in virgin as well as lactating mammary tissue.