MODULATION OF ELONGATION FACTOR-I DELTA (EF-1-DELTA) EXPRESSION BY ONCOGENES IN HUMAN EPITHELIAL-CELLS

A cDNA clone covering part of the C-terminal domain of human EF-1 delt a was isolated from mammary cancel cells by subtractive hybridisation. The higher expression of EF-1 delta in the tumours suggested that mal ignant transformation in vivo requires an increase in translation fact or mRNA and protein synthesis for entry into and transition through th e cell cycle. To explore the relation between cell division and EF-1 d elta expression, MCF-7 cells were treated with dexamethasone, an induc er of differentiation. There was no change in the mRNA levels of EF-1 delta in the dexamethasone-treated cells. To explore the relation betw een oncogenes and EF-1 delta expression, a variety of oncogenes were i ntroduced into human mammary epithelial cells (MCF-7) and human kerati nocytes (HaCaT). Despite high oncogene mRNA expression, there was no s ignificant change in the EF-1 delta mRNA level by v-src, c-erbB (EGF R eceptor), c-erbB-2, v-myc and v-fos oncogenes. However, overexpression of v-Ha-ras in HaCaT cells resulted in a three to five-fold decrease in the steady-state mRNA level of EF-1(delta). Taken together, the dat a provides further support on the interaction of translation factors a nd oncogenic transformation.