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Expression of Functional Epidermal Growth Factor Receptors in a Human Hematopoietic Cell Line¹

Departments of Medicine [J. O., R. T.] and Pathology [R. T.], University of California, San Diego, California; Salk Institute, La Jolla, California [R. H.]; Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York [B. G., E. G.]; and Rorer Biotechnology, King of Prussia, Pennsylvania [J. S.]

To test the feasibility of using the human epidermal growth factor receptor (EGFR) as a model for growth factor receptor action in human hematopoietic cells, we infected Burkitt lymphoma cells (Namalwa) with a recombinant amphotrophic retrovirus containing a thymidine kinase promoter-driven human EGFR complementary DNA and the neomycin resistance gene. Neomycin-resistant cells expressing surface EGFR were selected by cell sorting using anti-EGFR monoclonal antibody 225. The selected cells expressed a M_r 170,000 protein immunoprecipitated by monoclonal antibody 225 and apparently identical to EGFR from A431 carcinoma cells. Infected Namaiwa cells expressed 42,000 epidermal growth factor (EGF) binding sites/cell, and Scatchard analysis showed two affinities (K_d 5 nM and 0.5 nM). EGFR autophosphorylation was detected using antiphosphotyrosine antibodies after 5 min exposure to EGF. EGF binding induced rapid EGFR internalization (t_1/2 = 9 min) and mobilization of transferrin receptors to the cell surface within 1 min. In fetal bovine serum-containing and serum-free cultures, EGF did not stimulate Namalwa cell proliferation. However, in the presence of 1.25% dimethyl sulfoxide (DMSO), EGF caused a dose-dependent increase in DNA synthesis. DMSO induced a cell cycle block in G₁, which was partially reversed by EGF. DMSO induced changes in some B-cell markers suggesting cellular differentiation and increased surface EGF receptor number. Cells grown in DMSO and EGF were established as an EGF-dependent cell line for >12 weeks, whereas cells grown in DMSO without EGF died within 1–2 weeks. Namalwa cells expressing EGFR demonstrated more rapid tumor growth in athymic mice. These studies demonstrate expression of functional EGFR mediating early biochemical and growth responses in a human hematopoietic cell, and indicate that EGFR can be used as an effective model in human hematopoietic cells. Results using DMSO are consistent with studies in other human leukemia cells indicating that agents inducing differentiation can restore growth factor dependence in previously factor-independent leukemia cells.

¹ This work was supported by NIH Grants CA32094 and CA23150.

² To whom requests for reprints should be addressed, at University of California Medical Center (H-720T), 225 Dickinson Street, San Diego, CA 92103.

Received 1/22/90. Accepted 9/21/90.

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