Transformation of Mammalian Cells by Constitutively Active MAP Kinase Kinase

TLDR

MAP kinase kinase (MAPKK) activates MAP kinase in a signal transduction pathway mediating cellular responses to growth and differentiation factors, and oncogenes such as ras, src, raf, and mos are thought to transform cells by prolonging MAPKK activation. The study aimed to test whether constitutively active MAPKK mutants could transform cells. Constitutively active MAPKK mutants were engineered with basal activities up to 400‑fold higher than unphosphorylated wild‑type kinase. Expression of these mutants activated AP‑1 transcription, formed transformed foci, grew in soft agar, and were highly tumorigenic in nude mice, demonstrating that constitutive MAPKK activation is sufficient for cell transformation.

Abstract

Mitogen-activated protein (MAP) kinase kinase (MAPKK) activates MAP kinase in a signal transduction pathway that mediates cellular responses to growth and differentiation factors. Oncogenes such as ras , src , raf , and mos have been proposed to transform cells by prolonging the activated state of MAPKK and of components downstream in the signaling pathway. To test this hypothesis, constitutively active MAPKK mutants were designed that had basal activities up to 400 times greater than that of the unphosphorylated wild-type kinase. Expression of these mutants in mammalian cells activated AP-1-regulated transcription. The cells formed transformed foci, grew efficiently in soft agar, and were highly tumorigenic in nude mice. These findings indicate that constitutive activation of MAPKK is sufficient to promote cell transformation.