Translation in Xenopus oocytes of messenger RNA from A431 cells for human epidermal growth factor receptor proteins.

Abstract

Translation of messenger RNAs (mRNAs) for human epidermal growth factor receptor (EGF-R) proteins was accomplished in a Xenopus oocyte translation system. Translation of these mRNAs in rabbit reticulocyte lysates and wheat germ extracts were unsuccessful, in accordance with the general difficulty in translating mRNAs for membrane-bound glycoproteins in conventional heterologous cell-free systems. Total poly(A)+RNA from a human epidermoid carcinoma cell line A431 was injected into oocytes from Xenopus laevis. After incubation in the presence of [35S]methionine, the oocytes were homogenized and the supernatant incubated with several different polyclonal antibodies (IgGs) against the human EGF-R. Immunocomplexes were bound to protein A-Sepharose, washed extensively, and electrophoresed in sodium dodecyl sulfate-polyacrylamide gels. A protein of Mr = 160,000, corresponding to the EGF-R glycoprotein, was specifically precipitated from RNA-injected oocytes by each of the anti-EGF-R IgGs. This protein was not detectable in the immunoprecipitates from uninjected oocytes nor was it precipitated from RNA-injected oocytes by IgG from normal rabbit serum or IgG to an unrelated protein. A second protein of Mr = 100,000 was also immunoprecipitated from the homogenates of RNA-injected oocytes. This product corresponds to the EGF-R-related protein, present in A431 cells, which is structurally similar to the EGF-R (Weber et al., 1984). Thus, frog oocytes provide an efficient and generally applicable heterologous system for translation of mRNAs for large glycoproteins such as growth factor receptors. In addition, successful immunoprecipitation of translated products in this system provides a method for assay of mRNAs where biological activity of the proteins cannot be monitored.