The proto-oncogene termed erbB2 (or HER2) encodes a 185 kDa transmembrane tyrosine kinase molecule designated p185erbB2.  The overexpression of this receptor molecule correlates strongly with a poor prognosis in a number of human cancers including, among others, breast, ovarian, endometrium, fallopian tube, cervix, and colon (Nowak, F., et al.,  Exp.  Cell Res.  231:251–259; 1997; Cirisano, F. D. and Karlan, B. Y., J. Soc.  Gynecol.  Investig.  3(3):99–105; 1996).  Variously spliced transcripts of the heregulin (HRG) gene have been found to indirectly stimulate p185erbB2 through transphosphorylation or receptor heterodimerization with erbB3 and p180erbB4.  A 45 kDa protein, designated HRG-alpha, specifically induces tyrosine phosphorylation of p185erbB2 and has been purified from the conditioned medium of a human breast tumor cell line (Holmes, W. E., et al.,  Science 256:1205–1210; 1992).  A second, related HRG molecule of 52 kDa, which may be the product of a novel gene, rather than a novel HRG gene splice product, has been identified which exhibits similar characteristics including induction of transient membrane ruffling, lamellipodia formation, cell motility and proliferation of human breast cancer cells (Kung, W., et al.,  Biochem.  Biophys.  Res.  Commun.  202(3):1357–1365; 1994).  In addition, more recent studies have reported that heregulins can induce tyrosine phosphorylation not only of p185erbB2, but of several additional EGFR-related family members including erbB3 and p180erbB4 (Tzahar, E., et al.,  J. Biol.  Chem.  269:25226–25223; 1994; Plowman, G. D., et al.,  Nature 366:473–475; 1993). 
Lewis and colleagues (Cancer Res.  56:1457–1465; 1996) recently performed an extensive analysis of the effects of the heregulin family of proteins on a panel of breast and ovarian tumor cell lines.  The biological responses to HRG were also compared to EGF and to the growth-inhibitory anti-ErbB2 antibody 4D5.  In nearly all cases, HRG stimulation of DNA synthesis correlated with positive effects on cell cycle progression and cell number and with enhancement of colony formation in soft agar.  In addition to the effects of the heregulin family of proteins on breast and ovarian cells, similar effects have also been recently observed on human Schwann cells (Levi, A. D., et al.,  J. Neurosci.  15(2):1329–1340; 1995; Morrissey, T. K., et al.,  Proc.  Natl.  Acad.  Sci.  USA 92(5):1431–1435; 1995) suggesting that the heregulin family of proteins play a key role in the genesis of a number of cancers. 
The heregulin family of proteins consists at least of a number of splice variants of heregulin, the Neu differentiating factor, the glial growth factors-I, -II, and -III, and a protein that stimulates muscle acetylcholine receptor synthesis (ARIA).  In addition to the obvious role such polypeptides may play in oncogenic events, these proteins have also been exploited as Pseudomonas exotoxin A fusion proteins to inhibit the growth of several mammary carcinoma cell lines as well as to cause growth retardation of transplanted human breast tumor cells in mice (Jeschke, M., et al.,  Int.  J. Cancer 60(5):730–739;1995). 
Thus, there is a need for polypeptides that function as regulators of oncogenic events and existing tumors.  Therefore, there is a need for identification and characterization of such human polypeptides which can play a role in detecting, preventing, ameliorating or correcting such disorders.