ERBB2 EXPRESSION INCREASES THE SPECTRUM AND POTENCY OF LIGAND-MEDIATED SIGNAL-TRANSDUCTION THROUGH ERBB4

Interleukin 3-dependent murine 32D cells do not detectably express mem bers of the ErbB receptor family and do not proliferate in response to known ligands for these receptors, 32D transfectants were generated e xpressing human ErbB4 alone (32D.E4) or with ErbB2 (32D.E2/E4), Epider mal growth factor (EGF), neuregulin 1-beta (NRG1-beta), betacellulin ( BTC), transforming growth factor-alpha (TGF-alpha), heparin binding-EG F (HB-EGF), and amphiregulin were analyzed for their ability to mediat e mitogenesis in these transfectants. 32D.E4 responded mitogenically t o NRG1-beta and BTC. Surprisingly, EGF also induced significant DNA sy nthesis and TGF-alpha was negligibly mitogenic on 32D.E4 cells, wherea s HB-EGF and amphiregulin were inactive, Although coexpression of ErbB 2 with ErbB4 in 32D.E2/E4 cells did not significantly alter DNA synthe sis in response to NRG1-beta or BTC, it greatly enhanced mitogenesis e licited by EGF and TGF-alpha and unmasked the ability of HB-EGF to ind uce proliferation. EGF-related ligands that exhibited potent mitogenic activity on 32D.E2/E4 cells at low concentrations induced adherence, morphological alterations, and up-regulation of the Mac-1 integrin and Fc gamma RII/III at higher concentrations. While I-125-EGF could be s pecifically crosslinked to both 32D.E4 and 32D.E2/E4 cells, its crossl inking capacity was greatly enhanced in the cotransfected cells. The a bility of the various ligands to mediate proliferation and/or adhesion in the two transfectants correlated with their capacity to induce sub strate tyrosine phosphorylation and to initiate and sustain activation of mitogen-activated protein kinase, We conclude that the ability of ErbB4 to mediate signal transduction through EGF-like ligands is broad er than previously assumed and can be profoundly altered by the concom itant expression of ErbB2.