Elk3 from Hamster—A Ternary Complex Factor with Strong Transcriptional Repressor Activity.

Elk3 belongs to the Ets family of transcription factors, which are regulated by the Ras/mitogen-activated proteinkinase-signaling pathway. In the absence of Ras, this protein is a strong inhibitor of transcription andmay be directly involved in regulation of growth by downregulating the transcription of genes that are activatedduring entry into G. We have isolated theElk3 gene from the Chinese hamster ovary(CHO) cell line and investigated the transcriptional potential of this factor. Transient transfections revealedthat, in addition to its regulation of thepromoter, Elk3 from CHO cells seems to inhibit other promoterscontrolling expression of proteins involved in G/S phase progression; Cyclin D1 and DHFR. As has beendescribed for the Elk3 homologs Net (Mouse) and Sap-2 (Human), the results of the present study further indicatethat hamster Elk3 is a target of the Ras-Raf-MAPK pathway, and cotransfections with constitutivelyactive H-relieves its negative transcriptional activity. No cells stably expressing exogenous Elk3 could beobtained, possibly due to an unspecified toxic or growth retarding effect. These findings support a possiblerole for Elk3 in growth regulation and reveal a high degree of homology for this protein across species. [ABSTRACT FROM AUTHOR]