PARENT SESSION
SLIDE SESSION 11: GENE REGULATION & FUNCTION
Chairs: Michael Pallidino, Jeanne Wison-Rawles, Leslie Skalla (Trainee)
Univ Ottawa-Arts Hall 257
1:30 PM-3:30 PM

CONTROL OF THE HUMAN CHORIONIC GONADOTROPIN-ALPHA AND -BETA GENES BY ETS-2 AND RAS.

Ghosh, Debjani¹, Ezashi, Toshihiko¹, Roberts, Robert¹, ¹

ABSTRACT- The production of human chorionic gonadotropin (hCG) by trophectoderm begins at the blastocyst stage and is quickly up-regulated in order to provide luteal support for the pregnant mother. Although much is known about the transcriptional control of both hCG-alpha and -beta in differentiated trophoblast cells, the initial stages of gene activation are poorly understood. Several genes, including those for interferon-tau, expressed in trophectoderm and silent in the inner cell mass of developing embryos, are under the transcriptional control of Ets-2. The activity of Ets-2, in turn, can be modulated through the MAP-kinase pathway. Here, we have examined whether Ets-2 and constitutively activated Ras, an upstream component of the MAP-kinase cascade, have any role in controlling expression of hCG-alpha and -beta. In initial experiments performed in human choriocarcinoma (JAr) cells, transient co-transfection of hCG-alpha promoter (-1500, -680, and -232 bp) luc reporter constructs with Ets-2 and Ras expression plasmids had little effect. However, when the experiments were repeated in 3T3 murine fibroblasts, Ets-2 and Ras were each able to increase promoter activity of the hCG constructs 4- to 5-fold. When transfected together, there was a synergistic effect, with luc expression increasing over 100-fold for the -680 promoter and 150-fold for the -232 construct. Mutation of Thr 72 of Ets-2, which is a target for MAP-kinase phosphorylation, reduced but did not abolish the combined effects of Ets-2 and Ras. Essentially similar data were obtained in 3T3 cells with -300 and -150 hCG-beta promoters. Both were transactivated more than 100-fold by the combined action of Ets-2 and Ras. The results suggest that Ets-2 and the MAP-kinase pathway might play key roles in the initial up-regulation of hCG-alpha and -beta in trophoblast. Supported by NIH Grant HD 21896.

KEY WORDS: trophoblast, pregnancy, chorionic gonadotropin, transcription factor