Robinson M J, Beinke S, Kouroumalis A, Tsichlis P N, Ley S C
Division of Immune Cell Biology, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom.
Mol Cell Biol. 2007 Nov;27(21):7355-64. doi: 10.1128/MCB.00301-07. Epub 2007 Aug 20.
Tumor progression locus 2 (TPL-2) kinase is essential for Toll-like receptor 4 activation of the mitogen-activated protein kinase extracellular signal-regulated kinase (ERK) and for upregulation of the inflammatory cytokine tumor necrosis factor (TNF) in lipopolysaccharide (LPS)-stimulated macrophages. LPS activation of ERK requires TPL-2 release from associated NF-kappaB1 p105, which blocks TPL-2 access to its substrate, the ERK kinase MEK. Here we demonstrate that TPL-2 activity is also regulated independently of p105, since LPS stimulation was still needed for TPL-2-dependent activation of ERK in Nfkb1(-/-) macrophages. In wild-type macrophages, LPS induced the rapid phosphorylation of serine (S) 400 in the TPL-2 C-terminal tail. Mutation of this conserved residue to alanine (A) blocked the ability of retrovirally expressed TPL-2 to induce the activation of ERK in LPS-stimulated Nfkb1(-/-) macrophages. TPL-2(S400A) expression also failed to reconstitute LPS activation of ERK and induction of TNF in Map3k8(-/-) macrophages, which lack endogenous TPL-2. Consistently, the S400A mutation was found to block LPS stimulation of TPL-2 MEK kinase activity. Thus, induction of TPL-2 MEK kinase activity by LPS stimulation of macrophages requires TPL-2 phosphorylation on S400, in addition to its release from NF-kappaB1 p105. Oncogenic C-terminal truncations of TPL-2 that remove S400 could promote its transforming potential by eliminating this critical control step.
肿瘤进展位点2（TPL-2）激酶对于Toll样受体4激活丝裂原活化蛋白激酶细胞外信号调节激酶（ERK）以及在脂多糖（LPS）刺激的巨噬细胞中上调炎性细胞因子肿瘤坏死因子（TNF）至关重要。ERK的LPS激活需要TPL-2从相关的NF-κB1 p105释放，NF-κB1 p105会阻止TPL-2接近其底物ERK激酶MEK。在这里，我们证明TPL-2活性也独立于p105进行调节，因为在Nfkb1（-/-）巨噬细胞中，TPL-2依赖的ERK激活仍需要LPS刺激。在野生型巨噬细胞中，LPS诱导TPL-2 C末端尾巴中丝氨酸（S）400的快速磷酸化。将这个保守残基突变为丙氨酸（A）会阻断逆转录病毒表达的TPL-2在LPS刺激的Nfkb1（-/-）巨噬细胞中诱导ERK激活的能力。TPL-2（S400A）的表达也未能在缺乏内源性TPL-2的Map3k8（-/-）巨噬细胞中重建ERK的LPS激活和TNF的诱导。一致地，发现S400A突变会阻断LPS对TPL-2 MEK激酶活性的刺激。因此，除了TPL-2从NF-κB1 p105释放外，LPS刺激巨噬细胞诱导TPL-2 MEK激酶活性还需要TPL-2在S400上的磷酸化。去除S400的TPL-2致癌性C末端截短可能通过消除这一关键控制步骤来促进其转化潜能。
