mTOR pathway alterations in chromophobe renal cell carcinoma: Impact on metastasis development and overall survival

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Background: Chromophobe renal cell carcinoma (chRCC) is a histologically and molecularly distinct class of rare renal cancer representing less than 5% of the kidney tumors. Molecular knowledge of this disease is limited, as well as prognostic factors for relapse if localized disease or response in the metastatic setting. Methods: From our database form different Spanish Hospitals, we identified a series of 89 chRCC with a localized stage and 3 patients stage IV at first diagnoses. We performed an in-depth characterization of mTOR pathway alterations, through targeted NGS and immunohistochemistry (IHC) of phospho-S6, tuberin and PTEN, and determined their impact on metastasis development and overall survival. Mutations in mitochondria and telomere maintenance genes were also assessed. TCGA kidney chromophobe project (KICH, n=64) was used for validation. Results: TP53, mTOR pathway ( MTOR, TSC2 or TSC1), telomere-related genes ( ATRX, TERT promoter or DAXX) and respiratory chain complex I, were mutated in 28%, 16%, 15% (26, 14, 12 of 87) and 15% (14 of 73) of primary tumors. PTEN and FLCN were mutated in four and three patients, respectively, two with bilateral tumors. IHC of phospho-S6 revealed positive staining in 37% of primary tumors (21 of 57), in association with MTOR, TSC2 and TSC1 mutations (P=0.009). Negative PTEN staining in 82% of cases (46 of 56) suggested PTEN loss as a chRCC characteristic, and was mutually exclusive with MTOR, TSC2 or TSC1 mutations (P=0.001). Weak or negative tuberin staining correlated with TSC2 mutations (P=0.02). Regarding metastasis development, TP53 mutations were enriched in malignant tumors (P=0.018), while telomere-related mutations showed a trend in the same direction. mTOR pathway mutations were associated with worse outcome. Overall survival in multivariable analysis adjusting for tumor stage gave a Hazard Ratio of 6.5 (P=0.009) This association was confirmed in TCGA-KICH (HR=11.9, P=0.05). Conclusions: Our study provides new genomic knowledge of chRCC and identifies novel markers of poor survival. Furthermore, we identified patients with mutations in mTOR pathway genes that showed high sensitivity to mTOR inhibitors.

Nitrate reductase of green algae is located in the pyrenoid

Antibodies against nitrate reductase from Monoraphidium braunii have been used to determine the antigenic relationships of nitrate reductases from different green algae. Nitrate reductases from Chlamydomonas reinhardii, Chlorella fusca, Dunaliella salina, and Scenedesmus obliquus, were inhibited by, and cross-reacted with, antibodies raised against the enzyme from Monoraphidium braunii.These antibodies were also used to determine, by immunoelectron microscopy, the intracellular location of nitrate reductase in the aforementioned green algae. In all cases, the enzyme was specifically located in the pyrenoid.

Nitrate Reductase from Monoraphidium braunii: Immunocytochemical Localization and Immunological Characterization

Homogeneous nitrate reductase (EC 1.6.6.2) from Monoraphidium braunii was obtained by means of affinity chromatography in blue-Sepharose and gel filtration. After electrophoresis in polyacrylamide, gel slices containing pure nitrate reductase were disrupted and injected into previously unimmunized rabbits. The antiserum produced after several weeks was found to inhibit the different activities of nitrate reductase to a similar degree. Monospecificity of the antiserum was demonstrated by Ouchterlony double diffusion and crossed immunoelectrophoresis. The antibodies were purified by immunoabsorption to Sepharose-bound nitrate reductase.The intracellular location of nitrate reductase in green algae was examined by applying an immunocytochemical method to M. braunii cells. Ultrathin frozen sections were first treated with immunopurified anti-nitrate reductase monospecific antibodies, followed by incubation with colloidal gold-labeled goat antirabbit immunoglobulin G as a marker. The enzyme was specifically located in the pyrenoid region of the chloroplast.