A PROTEIN INVOLVED IN CALCIUM SENSING OF THE HUMAN PARATHYROID AND PLACENTAL CYTOTROPHOBLAST CELLS BELONGS TO THE LDL-RECEPTOR PROTEIN SUPERFAMILY

Monoclonal anti-parathyroid antibodies have been utilized to isolate a single-chain glycoprotein of 500 kDa, which apparently acts as a sens or of the extracellular calcium concentration and is expressed on the surface of human parathyroid, placental, and kidney tubule cells. The present contribution reports the isolation of a cDNA clone encoding th is protein in human placenta and subsequent Northern blots confirming the mRNA expression also in human parathyroid and kidney cells. Close similarity in sequence as well as in tissue distribution is demonstrat ed with the rat Heymann nephritis antigen, a kidney tubule glycoprotei n with calcium-binding ability. The 500-kDa protein belongs to the LDL -receptor superfamily of glycoproteins, claimed to function primarily as protein receptors and characterized by functionally important calci um-binding capacity. It is proposed that the currently identified prot ein constitutes part of a common structure for the sensing of extracel lular calcium concentrations and influences calcium homeostasis in dif ferent organs. (C) 1994 Academic Press, Inc.