TRIB1 antibody, also called gprotein coupled receptor induced, skip1, gig2, c8fwATP, functions in binding protein binding, protein kinase inhibitor activity, and protein serine/threonine kinase activities. Overexpression of TRIB1 in HeLa cells repressed the basal activity of the IL8 promoter by inhibiting AP1 activity. Overexpression of TRIB1 inhibited oncogenic Ras -driven AP1 activation and MEKK1-mediated AP1 activation. ERK activation was enhanced by TRIB1. Coimmunoprecipitation and yeast 2-hybrid assays showed that MEK1 interacted with both TRIB1 and TRIB3, and MKK4 interacted specifically with TRIB1. Cotransfection of MKK4 enhanced the level of TRIB1, indicating that the TRIB-MAPKK interaction stabilized TRIB1.