A MONOCLONAL-ANTIBODY TO THE HUMAN C-ERBB3 PROTEIN STIMULATES THE ANCHORAGE-INDEPENDENT GROWTH OF BREAST-CANCER CELL-LINES

The c-erbB3 protein is a member of the type I growth factor receptor f amily. It has a widespread pattern of expression in normal tissues and is overexpressed in about 20% of breast cancers. We have raised a spe cific monoclonal antibody, called SGP1, against the extracellular doma in of c-erbB3 which recognises the native form of the protein. The mon oclonal antibody was found to modestly but significantly stimulate the anchorage-independent cloning efficiency of the breast tumour cell li nes BT483 and T47D, both of which express the c-erbB3 protein. No effe ct was observed on 293 cells lacking expression, nor did a control iso type-matched antibody promote the growth of any of the eels tested. Th ese results suggest that the c-erbB3 protein may normally act as a gro wth factor receptor.