Tpl2/Cot Signals Activate ERK, JNK, and NF-κB in a Cell-type and Stimulus-specific Manner

Irina Lambertz,Aristides G. Eliopoulos,Michelle A. Kelliher,Keyong Du,Philip N. Tsichlis,Santasabuj Das,Jeonghee Cho

doi:10.1074/jbc.m412837200

Abstract

Macrophages and B-cells from Tpl2 knock-out mice exhibit a restricted defect in lipopolysaccharide and death receptor signaling that is limited to the activation of ERK. Here we show that Tpl2-/- MEFs exhibit defects in ERK, JNK, and NF-kappaB activation, or ERK activation only when stimulated with tumor necrosis factor-alpha (TNF-alpha) or interleukin-1beta, respectively. In addition, we show that the activation of Tpl2 by TNF-alpha depends on signals transduced by both TRAF2 and RIP1. Activated Tpl2 phosphorylates MKK4/SEK1 upstream of JNK and stimulates NF-kappaB DNA binding and transcriptional activity by mechanisms that are independent of the nuclear translocation of p50 and p65. Tpl2-transduced TNF-alpha signals instead promote the phosphorylation of p65 at Ser276 and modulate the spectrum of proteins associated with p65. Phosphorylation stimulates the transcriptional activity of NF-kappaB but does not affect its ability to bind DNA, which may be affected by the composition of the nuclear NF-kappaB complexes. These data confirm that defects caused by a single mutation may be cell-type and signal-specific and delineate the role of Tpl2 in the transduction of TNF-alpha signals that activate JNK and NF-kappaB in MEFs.

Highlights

Macrophages and B-cells from Tpl2 knock-out mice exhibit a restricted defect in lipopolysaccharide and death receptor signaling that is limited to the activation of ERK
To further explore the specificity of Tpl2 in the transduction of TNF-␣ signals, we examined the activation of ERK, JNK, and NF-␬B in TNF-␣-stimulated Tpl2ϩ/ϩ and Tpl2Ϫ/Ϫ macrophages and the activation of MAP kinases and NF-␬B in IL-1␤-treated Tpl2ϩ/ϩ and Tpl2Ϫ/Ϫ MEFs
We conclude that the signaling defect caused by a single mutation in a given cell type in response to a specific signal is not sufficient to predict the phenotypic effects of the mutation in the intact animal, which may depend on the functional interaction of signaling defects caused by the mutation in different cell types

Summary

Introduction

Macrophages and B-cells from Tpl knock-out mice exhibit a restricted defect in lipopolysaccharide and death receptor signaling that is limited to the activation of ERK. Phosphorylation stimulates the transcriptional activity of NF-␬B but does not affect its ability to bind DNA, which may be affected by the composition of the nuclear NF-␬B complexes These data confirm that defects caused by a single mutation may be cell-type and signal-specific and delineate the role of Tpl in the transduction of TNF-␣ signals that activate JNK and NF-␬B in MEFs. Tpl is a serine-threonine protein kinase that was cloned based on its ability to induce T-cell lymphomas when activated by proviral insertion in rodents [1, 2]. It is interesting to note that Tpl is required for the development of full-blown TNF-␣-induced arthritis and IBD, the pathobiology of the two syndromes may depend on signals originating in different cell types. TNFR1 bound to TRADD serves as an assembly platform for the binding of the TNF receptor-associated factor-2 (TRAF2) and the death domain containing serine-threonine protein kinase RIP1 (receptor-interacting kinase-1) [14, 15]

Methods

Results

Conclusion