Tumor Progression Locus 2 (Tpl2) Protein Kinase Contributes Tumor Growth And Metastasis Of Renal Cell Carcinoma

At least one-third of renal cell carcinoma (RCC) patients are diagnosed with metastases and an additional 20 to 40% of patients develop metastases after radical nephrectomy with curative intent. Although the treatment of advanced RCC has recently evolved to the use of VEGF-targeted antiangiogenic therapies, there have been no significant improvements in the mortality rate of RCC, most likely because currently available therapies are relatively ineffective. A full understanding of the molecular pathogenesis involved in the progression of RCC is important for the development of innovative treatment options. Tumor Progression Locus 2 (Tpl2/MAP3K8), is a serine-threonine kinase with an important physiological role in tumor necrosis factor, interleukin-1, CD40, Toll-like receptor and G protein-coupled receptor-mediated extracellular signal-regulated kinases (ERK1/ERK2), c-Jun NH2-terminal kinases (JNK), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and p38MAPK pathways. Previously identified as an oncogene, its overexpression is reported in many types of cancer and associated with metastatic potential. Inspection of transcriptome profiles registered in the oncomine database indicates that Tpl2 expression is differentially expressed in RCC compared to normal tissue. However, the relevance of Tpl2 in tumor growth and metastasis of RCC and the underlying mechanisms remain to be explored. To investigate a functional role of Tpl2 in the progression of RCC, the molecular effects of Tpl2 inhibition were examined in human RCC preclinical model using Caki-1 cells. In this study, we report a functional role for Tpl2 in RCC tumorigenesis and metastasis. Gene silencing with Tpl2 short hairpin RNA and treatment with a Tpl2 kinase inhibitor remarkably suppressed proliferation, focus formation potential, anoikis-resistance and cell-adhesion as well as in vitro cell migration/invasion capabilities in Caki-1 cells. Cell cycle assay showed that the anti-proliferation effect of Tpl2 shRNA was mediated by arresting cells in the G0/G1 phase. We found that interleukin 1β-induced phosphorylation of ERK or JNK was markedly suppressed by Tpl2 shRNA or Tpl2 kinase inhibitor. Furthermore, the orthotopically xenografted tumor growth of Caki-1 cells was significantly suppressed by Tpl2 knockdown with Tpl2 shRNA. An experimental metastasis assay also shows that Tpl2 inhibition suppressed the ability of Caki-1 cells to form lung metastases in a murine tail vein injection model. In clinical specimens of RCC, immunohistochemistry showed that Tpl2 expression levels in RCC specimens were significantly higher than those in normal renal tissues. These data suggest that Tpl2 may function as an oncogene linked to RCC and potential target for novel therapeutic modalities for advanced RCC. Citation Format: Hye Won Lee, Se Jeong Lee, Mi Young Song, Kyeung Min Joo, Byong Chang Jeong, Do-Hyun Nam. Tumor progression locus 2 (Tpl2) protein kinase contributes tumor growth and metastasis of renal cell carcinoma. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr C53.