FUNCTIONAL-CHARACTERIZATION OF COM, A DNA REGION REQUIRED FOR COOPERATION BETWEEN AP-1 SITES IN UROKINASE GENE-TRANSCRIPTION

The inducible uPA enhancer contains two phorbol ester responsive eleme nts: the combined PEA3/AP-1(A) and a downstream AP-1(A) site. The inte grity of all three sites is essential for enhancer activity, The inter posed 74 bp long DNA region (COM, Cooperation Mediator) is in turn req uired for the synergistic action of the PEA3/AP-1 and AP-1 sites, Here we present a characterization of the COM sequence: our results show t hat COM and COM-binding proteins (UEF, Urokinase Enhancer Factors) may play a structural role in the induction of the uPA enhancer by phorbo l-myristate-acetate (TPA), (1) COM has a bipartite structure (uCOM and dCOM) and each half contributes by about 50% to the COM-mediated TPA induction, (2) COM function is strictly dependent on its position, but not on its orientation and neither the entire COM nor individual UEF- binding sites can directly transactivate a test promoter, (3) The requ irement for COM in TPA-induction is partly eliminated by the deletion of COM sequence, However, also in the COM-deleted enhancer, integrity of the PEA3/AP-1, and AP-1, sites is essential for enhancer function, We conclude that COM and COM-binding proteins provide a structural sur face which facilitates the cooperation between the transactivator prot eins bound at the PEA3/AP-1, and AP-1, sites, Sequences homologous to uCOM are found in the promoters of other inducible genes, coding for p roteases, cytokines and chemokines: for example, in the promoter of th e MIP1 alpha/LD78 chemokine gene, a 15/18 nucleotides identity is foun d in a region mediating positive and negative functions in TPA inducti on. Thus, COM-like elements represent a general enhancer function whic h, although lacking an intrinsic transactivating capacity, modulates t he synergism between transcription factors bound to distant sites.