COEXPRESSION OF ERBB2 AND ERBB3 PROTEINS RECONSTITUTES A HIGH-AFFINITY RECEPTOR FOR HEREGULIN

The heregulin/neu differentiation factor gene products were purified a nd cloned based on their ability to stimulate the phosphorylation of a 185-kDa protein in human breast carcinoma cell lines known to express erbB2. However, not all cells that express erbB2 respond to heregulin , indicating that other components besides erbB2 may be required for h eregulin binding. Cells that are transfected with the closely related receptor, erbB3, display a single class of lower affinity heregulin bi nding sites than has been previously observed on breast carcinoma cell lines. Little or no stimulation of tyrosine phosphorylation in respon se to heregulin occurs in cells that are transfected with erbB3 alone. Transfection of cells with erbB3 and erbB2 reconstitutes a higher aff inity binding receptor, which is also capable of generating a tyrosine phosphorylation signal in response to heregulin. A monoclonal antibod y to erbB2 will inhibit heregulin activation of tyrosine phosphorylati on and binding in cells transfected with both receptors but not with e rbB3 alone. In cells expressing erbB2 and erbB3, both proteins become tyrosine-phosphorylated upon interaction with heregulin. Direct intera ction between heregulin and the two proteins was demonstrated by chemi cal cross-linking experiments using I-125-heregulin followed by immuno precipitation with antibodies specific for erbB2 or erbB3.