IDENTIFICATION OF A RECEPTOR FOR HUMAN MULLERIAN-INHIBITING SUBSTANCE

Mullerian inhibiting substance (MIS), a Sertoli cell-derived glycoprotein and member of the transforming growth factor-beta supergene family, plays a key down-stream role in mammalian sex determination. Identification of a receptor for MIS has now been achieved in a MIS-responsive human vulvar carcinoma cell line, A431, using fluorescein isothiocyanate labeling of recombinant human MIS (FITC-rhMIS) and RRAs with iodinated carboxy-terminal rhMIS. Confocal fluorescence microscopy of A431 cells incubated on ice with 30-nm concentrations of covalently bound FITC-rhMIS reveals specific punctate cell surface fluorescent signal. Cytosolic fluorescent signal is seen after incubation at 37 C for 1 h as well as occasional apparent perinuclear accumulation. FITC-rhMIS coincubated with molar excesses of unlabeled rhMIS in A431 cells eliminates cell surface and cytosolic fluorescent uptake. Double label experiments with FITC-rhMIS and tetramethyl rhodamine isothiocyanate epidermal growth factor establish separate binding of each ligand, displaceable, respectively, by large molar excesses of unlabeled rhMIS or epidermal growth factor. RRAs reveal a single, high affinity (K(d), 5.8 nm), saturable, low abundance binding species for carboxy-terminal rhMIS. Solubilized supernatants of A431 whole cells cross-linked with I-125-carboxy-terminal rhMIS identify a band with a mol wt of 88,000 on electrophoresis and autoradiography. This identification of a MIS receptor in A431 cells now permits the design of affinity purification protocols using rhMIS, followed by direct protein microsequencing.