GROWTH-FACTOR LIGANDS OF TYROSINE KINASE RECEPTORS ACTIVATE THE ROUS-SARCOMA VIRUS PROMOTER BY A RAS-DEPENDENT AND RAF-DEPENDENT MECHANISM

In PC12 cells, NGF and other ligands of tyrosine kinase receptors incr eased the activity of the Rous sarcoma virus (RSV) promoter. IGF-1 sti mulated the RSV promoter in SH-SY5Y neuroblastoma cells. This promoter was also activated by oncogenic Ras and Raf in different cell types, and growth factor induction was inhibited by expression of dominant ne gative forms of ras and raf, showing that its effect is mediated by a Ras- and Raf-dependent mechanism. Therefore, the RSV promoter should n ot be used in the determination of transfection efficiency in the stud ies on regulation of gene expression by ligands of tyrosine kinase rec eptors, ras and raf.