Prolactin regulation of glycosylation-dependent cell adhesion molecule 1 expression in mouse mammary epithelial cells

By screening for differentially expressed genes in mammary glands of PRL-gene disrupted (PRL−/−) mice, it was found that glycosylation-dependent cell adhesion molecule 1 (GlyCAM 1) was a new target gene for PRL. GlyCAM 1 mRNA was expressed by mammary epithelial cell and the proteins was secreted into the mammary ductal lumens. Induction of GlyCAM 1 expression in HC11 cells required dexamethasone and PRL, whereas PRL by itself was sufficient to stimulate GlyCAM 1 expression in the primary mammary epithelial cells (PMEC) of mice. Further studies showed that PRL induced GlyCAM 1 expression through the Jak2/Stat5 pathway and the two tandemly linked Stat5 binding sites (GAS1 and GAS2) in the proximal promoter region were crucial and synergistically responded to PRL. The synergy was resulted from forming Stat5 tetramer on the two tandemly linked GAS sites. Interruption of tetramer formation by mutation of a tryptophan to alanine (W37A), and a leucine to serine (L83S) in the N terminus of Stat5A blocked the synergistic effect between the two tandemly linked GAS elements and the endogenous GlyCAM 1 expression.; The human GlyCAM 1 homologue was identified by aligning the mouse proximal promoter sequence to the human genomic databases. Human GlyCAM 1 has features shared with the GlyCAM 1 genes in mice, cattle and camels, though the encoding sequences diverge greatly between species. hGlyCAM 1 mRNA was expressed in the human breast tissue, and various human breast cancer cell lines. Similarly, PRL induce hGlyCAM 1 expression via Jak2/Stat5 pathway. Surprisingly, no synergy was found between the conserved tandem GAS elements in the hGlyCAM 1 promoter.