STIMULATION OF PROLIFERATION OF A HUMAN OSTEOSARCOMA CELL-LINE BY EXOGENOUS ACIDIC FIBROBLAST GROWTH-FACTOR REQUIRES BOTH ACTIVATION OF RECEPTOR TYROSINE KINASE AND GROWTH-FACTOR INTERNALIZATION

U2OS Dr1 cells, originating from a human osteosarcoma, are resistant t o the intracellular action of diphtheria toxin but contain toxin recep tors on their surfaces. These cells do not hare detectable amounts of fibroblast growth factor receptors, When these cells were transfected with fibroblast growth factor receptor 4, the addition of acidic fibro blast growth factor to the medium induced tyrosine phosphorylation, DN A synthesis, and cell proliferation. A considerable fraction of the ce ll-associated growth factor was found in the nuclear fraction. When th e growth factor was fused to the diphtheria toxin A fragment, it was s till bound to the growth factor receptor and induced tyrosine phosphor ylation but did not induce DNA synthesis or cell proliferation, nor wa s any fusion protein recovered in the nuclear fraction. On the other h and, when the fusion protein was associated with the diphtheria toxin B fragment to allow translocation to the cytosol by the toxin pathway, the fusion protein was targeted to the nucleus anti stimulated both D NA synthesis and cell proliferation, In untransfected cells containing toxin receptors but not fibroblast growth factor receptors, the fusio n protein tvas translocated to the cytosol and targeted to the nucleus , but in this case, it stimulated only DNA synthesis. These data indic ate that the following two signals are required to stimulate cell prol iferation in transfected U2OS Dr1 cells: the tyrosine kinase signal fr om the activated fibroblast growth factor receptor and translocation o f the growth factor into the cell.