Immediate early genes induced by H-Ras in thyroid cells

Expression of oncogenic v-H-Ras in the thyroid cell line FRTL-5 (FRTL-5(Ras )) results in uncontrolled proliferation, loss of thyroid-specific gene exp ression and tumorigenicity. Concomitant expression of constitutively activa ted MEK and pac, two major H-Ras downstream effecters, in FRTL-5 (FRTL-5(ME K/Rac)) recapitulates H-Ras effects on proliferation and morphology, In con trast to FRTL-5(Ras), however, FRTL-5(MEK/Rac) cells remain differentiated and are not tumorigenic, To find H-Ras induced genes potentially responsibl e for tumorigenicity and loss of differentiation, we have used subtractive suppression hybridization (SSH), a PCR-based cDNA subtraction technique, be tween de-differentiated and tumorigenic FRTL-5(Ras) cells and differentiate d and nontumorigenic FRTL-5(MEK/Rac) cells. We examined 800 of the cDNA clo nes obtained after subtraction and verified their levels of expression in t he two cell lines by reverse northern, identifying 337 H-Ras induced genes. By sequence analysis, we clustered 57 different genes. Among these, 39 wer e known genes (involved in diverse signal transduction processes regulating mitogenic activity, cell survival, cytoskeletal reorganization, stress res ponse and invasion) while the remaining 18 clones were novel genes. Among t he 57 H-Ras specific clones, we identified those genes whose expression is induced early by H-Ras, We suggest that these immediate-early genes may pla y a crucial role in H-Ras-mediated transformation in thyroid epithelial cel ls.