Purpose: To investigate the expression and function of neuregulin (NRG) isoforms in ovarian cancer cell lines and tumor samples.
Experimental design: Expression of NRG-1alpha and NRG-1beta proteins were detected by immunohistochemistry and mRNA by RT-PCR. erbB receptor levels and downstream signaling proteins were measured by Western blot analysis.
Results: Expression of NRG-1alpha and NRG-1beta proteins were detected by immunohistochemistry in 46 of 53 (87%) and 41 of 53 (77%) ovarian carcinomas, respectively. Serous carcinomas express higher levels of NRG-1alpha than endometrioid carcinomas (P = 0.017). NRG mRNA was detected by RT-PCR in 20 of 24 (83%) of ovarian carcinomas and eight of nine (89%) ovarian cancer cell lines. NRG-1alpha stimulated the growth of 5 of 14 cell lines whereas NRG-1beta stimulated 7 of 14 cell lines. The magnitude of NRG growth response was significantly associated with erbB2 expression levels. NRG-1alpha and -1beta (1 nM) growth-stimulated cell lines PE01 and PE06 demonstrated increased tyrosine phosphorylation of erbB2 and elevated tyrosine phosphorylation of ERK1 and ERK2. In contrast, the SKOV-3 cell line, the growth of which was unaffected, did not show these downstream responses. An anti-erbB3 receptor antibody (clone H3.105.5) blocked NRG-1beta growth changes and signaling in these cell lines. Conversely, the anti-erbB4 antibody (clone H4.72.8) enhanced NRG-beta1 growth stimulation. Herceptin also inhibited growth.
Conclusions: With NRG expression in the majority of ovarian carcinomas and cell lines, there is the potential for autocrine regulation of cell growth. Interfering with ligand-receptor interactions by receptor blocking antibodies suggests erbB3 is primarily involved in NRG-1beta-induced proliferation, with erbB4 having a more complex role.