Prolactin, alone or in combination with glucocorticoids, enhances tight junction formation and expression of the tight junction protein occludin in mammary cells

Tight junctions (TJ) between adjacent epithelial cells play an important ro le in maintaining mammary function in the differentiated mammary gland. Mou se mammary cell lines (HC11 and Comma-1D) were used to investigate the effe ct of the lactogenic hormones prolactin (PRL) and glucocorticoids on the fo rmation of mammary TJ. TJ formation was assessed by an increase in transepi thelial electrical resistance and a decrease in paracellular flux of radiol abeled inulin. Both PRL and the synthetic glucocorticoid dexamethasone (DEX ) stimulated TJ formation. The biggest effect on TJ formation was observed when both hormones were used in combination, but only when cells were pretr eated with DEX. The effects of PRL and DEX are mediated, at least in part, via expression of the transmembrane TJ protein occludin. In summary, these data are the first to show an effect of PRL on mammary TJ formation and the expression of TJ proteins, and confirm the TJ-stimulating effects of gluco corticoids that have been reported previously. (C) 1999 Elsevier Science Ir eland Ltd. All rights reserved.