Mitogen-activated kinase kinase kinase 1 regulates T cell receptor- and CD28-mediated signaling events which lead to NF-kappaB activation.

Optimal activation of Rel/NF-kappaB transcription factors in T lymphocytes requires a CD28-delivered co-stimulatory signal in addition to TCR engagement. Although, Rel/NF-kappaB transcription factors are critical regulators of many T cell functions, the mechanisms and molecules, which link the surface receptors to their activation, are poorly characterized. Using Jurkat T cells stimulated with superantigen presented on B7-positive APC, we showed that CD28- and TCR-stimulated NF-kappaB-dependent transcription is associated to the activation of IkappaB kinase beta (IKKbeta) and, to a lesser extent, of IkappaB kinase alpha (IKKalpha). A dominant negative mutant of the MAP3 kinase MEKK1, a kinase known to regulate the JNK pathway and to activate NF-kappaB-dependent transcription in many cell types, strongly inhibits CD28- and TCR-induced IKK activity, whereas the dominant negative mutants of the NF-kappaB-inducing kinase (NIK) did not exert any significant effects. In addition, TCR/CD28 stimulation results in the recruitment and autophosphorylation of endogenous MEKK1, whereas endogenous NIK was not detectably activated. Our data identify MEKK1 as a critical step in coupling signals initiated by TCR and CD28 to the downstream pathways which lead to both AP-1 and NF-kappaB activation in T lymphocytes.

nm23 influences proliferation and differentiation of PC12 cells in response to nerve growth factor.

The nm23 genes codify nucleoside diphosphate kinases, which have been shown to be involved in the regulation of microtubule dynamics. We have demonstrated previously that the association between the Nm23-M1 protein and cytoskeletal beta-tubulin correlates with cell differentiation. It is known that microtubules and microtubule-associated proteins are fundamental elements regulating neuronal differentiation. In the present study, we have investigated the ability of nm23 to influence nerve growth factor-induced PC12 cell differentiation. To this end, we have altered PC12 intracellular levels of nm23-M1 by means of sense and antisense transfections. In the presence of nerve growth factor, overexpression of nm23 delays cell cycle transition, rapidly induces neurite outgrowth, and increases the expression of neurofilament and microtubule proteins. On the contrary, down-regulation of nm23 enhances cell proliferation and inhibits neuronal differentiation. These findings indicate that neuronal cell proliferation and differentiation can be modulated by nm23 expression levels.