| dc.description.abstract | Renal cell carcinoma (RCC) is among the top ten cancers worldwide and accounts for >90% of cancers in kidney. Among them, clear-cell RCC (ccRCC) is the most common histological subtype accounting for more than 75% of all RCC cases. ccRCC is a highly vascularized and immunogenic tissue that is closely associated with inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene (found in ~80% of ccRCC patients). The VHL protein has been well-recognized as a key regulator of hypoxic response. However, it is still unclear how mutations in VHL, encoding the substrate-recognition subunit of an E3 ubiquitin ligase that targets the alpha subunit of hypoxia-inducible factor (HIF-α), can coordinate tissue inflammation and tumorigenesis. Endothelial cells (ECs) are a constituent of stromal cells, which are indispensable for every organ. ECs have traditionally been considered as a non-reactive barrier that separates blood from tissues. However, recently accumulating evidence has illustrated that ECs constitute a dynamic organ that actively participates in most if not all of the disease states, particularly in inflammatory response. Yet, how these ECs are involved in inflammatory regulation and tumorigenesis is less well documented, and whether VHL plays a role in coordinating these pathophysiological interactions is also unclear.
Previously we generated a conditional mouse Vhlh gene knockout in kidney tubules (VhlhKO), which results in severe inflammation and fibrosis in addition to hyperplasia and appearance of transformed clear cells. These results imply that inactivation of VHL can induce chronic inflammation, which may be an early step in ccRCC development. Interestingly, we found that endothelial cells in Vhlh knockout kidney, although not harboring any genetic modifications, show an enrichment of phosphorylated c-Jun N-terminal kinase (p-Jnk)–an inflammatory marker–that suggested a role in inflammation induced tumorigenesis. In addition, these ECs in Vhlh knockout mice show abnormal phenotypes resembling tumor ECs, including neoangiogenesis and leakage. In the transcriptome study of these ECs, we found a profound change in gene expression program of ECs from VhlhKO tissue compared with those in wild-type mice (WT). These genes with altered expression are mainly involved in inflammatory response and mesenchymal transition.
Importantly, we demonstrate that oncostatin M (OSM) is a major regulator that mediates the interaction between VHL mutant kidney tubule cells and the ECs. The expression of OSM is upregulated in VHL-deficient epithelial cells and can induce overexpression of OSMR in ECs, thus forming a self-perpetuating positive signaling loop. In vitro, OSM induces EC activation and endothelial-mesenchymal transition (EndoMT) that leads to increase of vascular permeability and the number of invaded kidney cancer cells. These OSM-activated ECs also induce macrophage polarization toward M2/TAM like phenotype. Knockdown of VHL in renal tubule cells (HK-2) results in upregulation of OSM. In coculture system, we found that HK-2 with VHL knockdown could induce activation of EC, which could be recused by attenuating OSM pathway in ECs by knockdown of OSMR receptor or neutralizing OSM in cocultured media.
In vivo, attenuating OSM pathway in ECs by generating Osmr knockout in VhlhKO tissue (DBKO tissue) could recuse the abnormal phenotypes of ECs in VhlhKO tissue including reduced angiogenesis (CD31+ cells number), secreted E-Selectin (sSELE; marker of EC activation), vascular leakage and tumor-endothelial-cells related morphologies. In addition, DBKO also recuses the phenotypes of VhlhKO mice that are related to ccRCC, including inflammatory foci, fibrosis, proliferation index (Ki-67+ cells) and macrophage infiltration (F4/80+ cells). Consistent with the results in genetic modification, in the pharmacological treatment, tofacitinib (a Janus kinase inhibitor) could markedly alleviate the activated EC index and inflammatory phenotype of VhlhKO tissue.
Finally, the Vhlh mutant microenvironment can enhance metastasis of exogenous tumors, both of the mouse melanoma (B16) and human ccRCC (786-O) cells. Thus, OSM signaling initiates reconstitution of inflammatory and tumorigenic microenvironment of VHL-deficient renal tubule cells, which play a critical role in ccRCC initiation and metastasis. Our results provide an insight regarding ECs in inflammation related cancer, and suggest OSM pathway as a novel target for prevention and treatment of early-onset and metastasis of ccRCC. | en_US |