2 ERBB-4 TRANSCRIPTS ARE EXPRESSED IN NORMAL BREAST AND IN MOST BREAST CANCERS

ErbB-4 is a recently described member of the epidermal growth factor r eceptor (EGFR) family which together with erbB-3 acts as a receptor fo r a group of ligands known as the neuregulins (NRGs) or heregulins (HR Gs), Unlike the EGFR and erbB-2 relatively little is known about the e xpression of erbB-4 in human tumours. Using RT-PCR and Southern blotti ng analysis we have investigated the expression of erbB-4 mRNA in a ra nge of human tumour cell lines and in normal and malignant breast tiss ue. Using primers which amplified a 658 base pair (bp) region correspo nding to part of the cytoplasmic domain of c-erbB-4 we found the recep tor was expressed in some but not all breast and ovarian tumour cell l ines and also in a glioma cell line. The highest level of erbB-4 expre ssion was found in the ovarian carcinoma OVCAR-3 and the breast carcin oma T-47D, In all cell lines where the 'full-length' erbB-4 was detect ed, a second previously undescribed c-erbB-4 sequence was also found a s a 610 bp PCR product. The alternative PCR product was identical in s equence to c-erbB-4 except for a deletion of 48 bp which encodes a con sensus phosphatidylinositol 3-kinase (PI3K) binding site. This suggest ed that the two forms of erbB-4 might interact with different intracel lular signalling pathways and therefore influence a wider variety of c ellular responses to heregulin than previously thought. Expression of both erbB-4 variants was found in 7/7 normal breast tissues but only i n 9/12 breast tumours analysed. In line with the terminology of Eleniu s et nl, (1997b) we have designated the two isoforms of the C-terminal transcripts as CT-a (full-length) and CT-b which lacks the PI3K bindi ng motif, These results identify suitable cell lines for the further i nvestigation of erbB-4 expression and function and suggest that the ro le of erbB-4 in breast cancer warrants further investigation with larg er numbers of normal and malignant breast tissues.