HYPERTONIC INDUCTION OF THE CELL-ADHESION MOLECULE BETA(1)-INTEGRIN IN MDCK CELLS

Cells of many organisms adapt tit osmotic stress by accumulating compa tible organic osmolytes. In Madin-Darby canine kidney (MDCK) cells, a renal epithelial cell. line widely used as a culture model for the stu dy of osmotic regulation in mammals, extracellular hypertonicity induc es genes responsible for the accumulation of organic osmolytes. We hav e recently cloned from these cells a partial cDNA corresponding to a m ember of the transmembrane 4 superfamily (tetraspan) family, CD9 antig en, and demonstrated its induction by hypertonicity [D. Sheikh-Hamad, J. D. Ferraris, J. Dragolovich, H. G. Preuss, M. B. Burg, and A. Garci a-Perez. Am. J. Physiol. 270 (Cell Physiol. 39): C253-C258, 1996]. An association between CD9 and potential regulatory proteins, such as the heparin-binding epidermal growth factor-like protein and the cell adh esion molecule beta(1)-integrin, has been reported. Here, using beta(1 )-integrin-specific monoclonal antibodies and an antisense oligonucleo tide probe, we demonstrate expression and hypertonic induction of beta (1)-integrin in MDCK cells, Induction of the mRNA and protein occurs i n 2 h and is maximal at 6 h, consistent with a regulatory role in the adaptation to osmotic stress. In addition, we show that accumulation o f organic osmolytes markedly attenuates the hyper tonic induction of t he mRNA, a feature shared with genes involved in hyperosmotic stress r esponse. Finally, we demonstrate that CD9 and beta(1)-integrin are exp ressed in association at the cell membrane. Our findings suggest the e xistence of a cluster of integral membrane proteins that includes but may not be Limited to CD9 and the adhesion molecule beta(1)-integrin, which may play a role in the adaptation of kidney cells to osmotic str ess, possibly at the regulatory level.