Expression of EGF receptor family members in myeloma cell lines. (A) ErbB1, ErbB2, ErbB3, ErbB4, and HB-EGF gene expression was assayed with RT-PCR in 9 myeloma cell lines. The A431 epidermoid carcinoma cell line was used as a control. Amplification of β actin shows the equivalence of the cDNA loading and amplification. Results are from one experiment representative of 3. (B) Myeloma cells or A431 cells were lysed and the lysates were immunoprecipitated with the H4.72.8 anti-ErbB4 or the LA-22 anti-ErbB1 antibody. The precipitated material was separated on a 7.5% SDS-PAGE and analyzed by Western blotting with a second anti-ErbB antibody (anti-ErbB4, clone C-18, or anti-ErbB1, clone LA-1). Results are of one experiment representative of 3.