Daniele D'Ambrosio*, Doreen A. Cantrell#, Luigi Frati*, Angela Santoni*, and Roberto Testi*$

* Department of Experimental Medicine, University of Rome "La Sapienza", 00161 Rome, Italy $ Deparment of Experimental Medicine and Biochemical Sciences, University of Rome "Tor Vergata", 00173 Rome, Italy # Lymphocyte Activation Laboratory, Imperial Cancer Research Fund, 44 Lincoln's Inn Fields, London WC2A 3PX, UK

Corresponding author: Roberto Testi

The involvement of p21ras in the induction of the early activation antigen CD69 was investigated in T cells. Expression of a constitutively active v-Ha-ras protein in Jurkat cells resulted in CD69 induction on the cell surface. Transfected Ras was shown to be constitutively activated and functionally efficient, since it could be immunoprecipitated in the GTP-bound form and it induced transactivation of an AP-1 consensus-CAT reporter gene. The requirement for Ras activation in TCR/CD3-mediated CD69 induction was also investigated. The expression of a dominant negative c-Ha-ras-N17 mutant markedly reduced the amount of GTP that could be immunoprecipitated from Ras proteins after TCR/CD3 triggering in Jurkat cells, and concomitantly decreased TCR/CD3-mediated CD69 induction. These results suggest a central role for Ras in TCR/CD3-mediated CD69 expression in T cells.