STUDIES ON THE BETACELLULIN RECEPTOR IN PANCREATIC AR42J CELLS

Betacellulin is a member of the epidermal growth factor family and con verts pancreatic AR42J cells into insulin-producing cells. This study was conducted to characterise the receptor for betacellulin in AR42J c ells. AR42J cells expressed two classes of binding sites for radioacti ve iodine labelled betacellulin, with Kd values of 4.6 x 10(-11) mol/l and 3.0 x 10(-10) mol/l. The binding of [I-125]betacellulin was inhib ited by unlabelled betacellulin in a dose-dependent manner, but epider mal growth factor was 50 fold less effective than betacellulin. Affini ty cross-linking showed a [I-125]betacellulin-binding protein with a m olecular weight of approximately 180 KDa. When this protein was immuno precipitated with antibody against epidermal growth factor receptors E rbB-1, ErbB-2, ErbB-3 or ErbB-4, it was immunoprecipitated only by the anti-ErbB-1 antibody. When the [I-125]betacellulin-labelled proteins were immunoprecipitated with a combination of the four ErbB antibodies , and the unprecipitated proteins were then immunoprecipitated with an ti-phosphotyrosine antibody, a 190 KDa protein was observed. Betacellu lin induced the tyrosine phosphorylation of ErbB-1, ErbB-2 and ErbB-4. Finally, while 100 pmol/l betacellulin converted all of the AR42J int o insulin-producing cells in the presence of activin A, 10 nmol/l epid ermal growth factor induced differentiation in only about 30% of the c ells. Higher concentrations of epidermal growth factor were less effec tive. Neu differentiation factor in the presence or absence of epiderm al growth factor was ineffective. These results indicate that betacell ulin binds to ErbB-1 and possibly another protein with a molecular wei ght of 190 KDa. The latter betacellulin-binding protein may be involve d in the differentiation-inducing activity of betacellulin.