HENSIN, A NEW COLLECTING DUCT PROTEIN INVOLVED IN THE IN-VITRO PLASTICITY OF INTERCALATED CELL POLARITY

Two forms of intercalated cells are present in kidney collecting tubul es, the a cell has apical endocytosis, apical H+-ATPase and basolatera l band 3, while beta cells have reversed polarity of these proteins an d no apical endocytosis, When a beta cell line was seeded at high dens ity, it changed into the a form, We previously showed that a partially purified 230 kD extracellular matrix protein of high density cells wa s able to retarget band 3 from apical to basolateral domains and stimu lated apical endocytosis in vitro (Van Adelsberg, J., J.C. Edwards, J. Takito, B. Kiss, and Q. Al-Awqati 1994. Cell. 76:1053-1061). We now p urify this protein, which was named hensin, to near homogeneity and fi nd that it belongs to the macrophage scavenger receptor cysteine rich (SRCR) family, An antibody, generated against a fusion protein made fr om a partial cDNA recognized a 230-kD protein in rabbit kidney and in the intercalated cell line. In vitro, the hensin antibody inhibited ex pression of apical endocytosis, Hensin was secreted in a polarized man ner and bound to the basolateral membrane and extracellular matrix. Im munohistochemistry of the kidney showed that it was expressed only in collecting tubules. Double immunofluorescence with hensin acid peanut lectin, H+-ATPase, or band 3 showed many patterns; most alpha-cells ha d hensin staining while 50% of beta-cells did not. These results sugge st that hensin may also be involved in the polarity reversal of interc alated cells in vivo.