6885

MAP3K7

mitogen-activated protein kinase kinase kinase 7;MAP3K7;mitogen-activated protein kinase kinase kinase 7

TGF-beta activated kinase 1|TGF-beta-activated kinase 1|transforming growth factor-beta-activated kinase 1

6q15

protein-coding

The dietary cis-polyunsaturated fatty acid, arachidonic acid, stimulates adhesion of metastatic human breast carcinoma cells (MDA-MB-435) to the extracellular matrix, but the molecular mechanisms by which fatty acids modify the behavior of these cells are unclear. Exposure to arachidonic acid activates multiple signaling pathways. Activation of p38 mitogen-activated protein kinase (p38 MAPK) is required for increased cell adhesion to type IV collagen, and this activation is sensitive to inhibitors of lipoxygenases, suggesting a requirement for arachidonic acid metabolism. The goals of the current study were to identify the one or more key metabolites of arachidonic acid that are responsible for activation of p38 MAPK and to elucidate the upstream kinases that lead to p38 MAPK activation. High performance liquid chromatographic analysis revealed that MDA-MB-435 cells metabolize exogenous arachidonic acid predominantly to 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE). Immunoblot analysis with antibodies specific to 15(S)-lipoxygenase-1 (LOX-1) and 15(S)-lipoxygenase-2 (LOX-2) demonstrated the expression of 15-LOX-2, but not 15-LOX-1, in these tumor cells. A LOX inhibitor, nordihydroguaiaretic acid, attenuated production of 15(S)-HETE and inhibited the phosphorylation of p38 MAPK following exposure to arachidonic acid. In contrast, overexpression of LOX-2 sensitized the cells to the addition of arachidonic acid, leading to increased activation of p38 MAPK. Addition of exogenous 15(S)-HETE to MDA-MB-435 cells stimulated cell adhesion to type IV collagen and activated the p38 MAPK pathway, including the upstream kinases transforming growth factor-beta1-activated protein kinase-1 (TAK1) and MAPK kinase 6. Transfection of these cells with a dominant negative form of TAK1 blocked arachidonic acid-stimulated p38 MAPK phosphorylation. These data demonstrate that 15(S)-LOX-2 generation of 15(S)-HETE activates specific growth factor receptor-related signaling pathways, thereby initiating signal transduction events leading to increased cell adhesion to the extracellular matrix.

BACKGROUND: Transforming growth factor-beta activated kinase-1 (TAK1) is a serine/threonine kinase in the mitogen-activated protein kinase kinase family. Previous studies have reported the role of TAK1 in cancer occurrence and progression; however, its role and clinical significance in esophageal squamous cell carcinoma (ESCC) has not been elucidated. We investigated the correlation of TAK1 expression and clinical outcome in T3N1-3M0 surgically resected ESCCs. METHODS: Tissue microarrays constructed of 234 surgically resected T3N1-3M0 ESCC primary tumors were used for TAK1 evaluation by immunohistochemistry. The clinical and prognostic significance of TAK1 expression was analyzed statistically. RESULTS: Positive expression of TAK1 was observed in 38.5% (90 of 234). The expression level of TAK1 in ESCCs at stage N2-3 was significantly higher than the expression level in those at stage N1 (p = 0.041). Patients with negative TAK1 expression demonstrated better overall survival than those with positive expression (median, 22.7 vs 17.4 months; p = 0.023). Multivariate analysis showed that TAK1 expression was an independent prognostic factor in ESCC (relative risk, 1.429; p = 0.021). CONCLUSIONS: TAK1 expression correlates with lymph node metastasis and is a negative, independent prognostic factor in resected T3N1-3M0 ESCCs.

Transforming growth factor-beta 1 (TGF-beta1) signaling in tumor cells has been implicated in tumor angiogenesis and metastasis by regulating matrix proteolysis. Although MMP-9/gelatinase-B is an important component of these TGF-beta1 responses, the mechanism of its regulation is not well understood. Here, we present evidence that TGF-beta-activated protein kinase 1 (TAK1) is critical for TGF-beta regulation of MMP-9 and the metastatic potential of breast cancer cell line MDA-MB-231. We found that suppression of TAK1 signaling by dominant-negative (dn) TAK1 or RNA interference (siRNA) reduces expression of MMP-9 and tumor cell invasion, without growth inhibition in cell culture. The orthotopic xenograft studies in SCID mice showed that suppression of TAK1 signaling by dn-TAK1 reduces tumor growth and formation of lung metastases. Dn-TAK1 reduced the proliferation Ki-67 index and neovasculature of orthotopic xenografts. TAK1-mediated regulation of MMP-9 involves NF-kappaB signaling. Dn-TAK1 reduces NF-kappaB transcriptional response and inhibition of NF-kappaB reduces expression of MMP-9 and activity of the MMP-9 promoter reporter. Together, these findings suggest that TAK1 contributes to TGF-beta1-mediated tumor angiogenesis and metastasis via a mechanism involving the TAK1-NF-kappaB-MMP-9 pathway.