Expression of human epidermal growth factor pressures cDNA in transfected mouse NIH 3T3 cells

Stable cell lines expressing the human epidermal growth factor (EGF) precursor have been prepared by transfection of mouse NIH 3T3 cells with a bovine papillomavirus-based vector in which the human kidney EGF precursor cDNA has been placed under the control of the inducible mouse metallothionein I promoter. Synthesis of the EGF precursor can be induced by culturing the cells in 5 mM butyric acid or 100 μM ZnCl2. The EGF precursor synthesized by these cells appears to be membrane associated; none is detectable in the cytoplasm. The size of the EGF precursor expressed by these cells is ≅ 150-180 kDa, which is larger than expected from its amino acid sequence, suggesting that it is posttranslationally modified, presumably by glycosylation. The EGF precursor was also detected in the conditioned medium from these cells, indicating that some fraction of the EGF precursor synthesized by these transfected cells may be secreted. Preliminary data suggest that this soluble form of the EGF precursor may compete with 125I-labeled EGF for binding to the EGF receptor. These cell lines should be useful for studying the processing of the EGF precursor to EGF as well as determining the properties and possible functions of the EGF precursor itself