CD9 ANTIGEN MESSENGER-RNA IS INDUCED BY HYPERTONICITY IN 2 RENAL EPITHELIAL-CELL LINES

In diverse organisms, cells adapt to hyperosmotic stress by accumulati ng organic osmolytes. Mammalian renal medullary cells are routinely un der osmotic stress. Two renal cell lines, Madin-Darby canine kidney (M DCK) and PAP-HT85, have been widely used to study mammalian osmotic re gulation. In these epithelial cells, extracellular hypertonicity induc es gene transcription of proteins directly involved in the metabolism and transport of organic osmolytes. This induction is relatively speci fic and not part of a generalized stress response. Little is known abo ut the signal transduction pathway between cellular detection of extra cellular osmolality and increased specific gene transcription. Here, u sing differential mRNA display polymerase chain reaction on MDCK cells in isotonic vs. hypertonic medium, we identify a cDNA product corresp onding to CD9 antigen mRNA. CD9 antigen is a cell surface glycoprotein originally found in cells of the immune system. Although CD9 antigen has been structurally characterized, its function is unclear. We furth er demonstrate that CD9 antigen mRNA is present in MDCK and PAP-HT85 c ells and that its mRNA abundance is induced by extracellular hypertoni city, but not by heat stress. Also, we show that accumulation of organ ic osmolytes markedly attenuates the CD9 mRNA induction, as only recen tly demonstrated with genes involved in the hyperosmotic stress respon se. This suggests a role for CD9 antigen in this response.