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Downregulation of RING ligase praja2 boosts receptor tyrosine kinases in kidney cancer

ABSTRACT: Clear cell renal cell carcinoma (ccRCC) is the most common variant of kidney cancer in the adult population. Late diagnosis, resistance to therapeutics and recurrence of metastatic lesions account for the highest mortality rate among kidney cancer patients. Identifying novel biomarkers for early cancer detection and the mechanisms underlying ccRCC growth and progression will provide clues to treat this aggressive malignant tumor. Here, we report that the RING ligase praja2 is a novel component of the endocytic system that supports clathrin-mediated receptor endocytosis. At molecular level, we identify the adaptor protein AP2 as a binding partner and substrate of praja2. Functionally, we demonstrate that praja2 is required for AP2-mediated receptor endocytosis and clearance. Downregulation of praja2 in RCC cells and tissues is associated with a marked upregulation of membrane receptors, as EGFR, VEGFR and TfR. A negative feedback loop links EGF signaling to proteolysis of praja2 and sustains downstream mitogenic and proliferative pathways. Restoring praja2 expression in RCC cells remarkably decreases EGFR levels, rewires cancer cell metabolism and inhibits RCC growth and metastatic diffusion. In praja2 knockout mice, upregulation of RTKs levels associates with profound histopathological renal alterations. Our findings identify praja2 as a component of the endocytic pathway that supports receptor endocytosis and clearance. Downregulation of praja2 in RCC cells, thus, sustains RTK signaling and promotes kidney cancer growth and diffusion.

INSTRUMENT(S): NextSeq 500

ORGANISM(S): Homo sapiens

SUBMITTER: Giorgio Giurato

PROVIDER: E-MTAB-11900 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Background: Clear cell renal cell carcinoma (ccRCC) is the most common kidney cancer in the adult population. Late diagnosis, resistance to therapeutics and recurrence of metastatic lesions account for the highest mortality rate among kidney cancer patients. Identifying novel biomarkers for early cancer detection and elucidating the mechanisms underlying ccRCC growth and progression will provide clues to treat this aggressive malignant tumor. Method: Expression studies of RING ligase praja2 and tyrosine kinase receptors (RTKs) in renal cell carcinoma was evaluated by immunoblot and immunohistochemistry. Gene transcription profiling in RCC cells was evaluated by RNA sequencing and Ingenuity Pathway Analysis. Imunofluorescence assays were used to evaluate the intracellular distribution and clearance of membrane receptors in cells devoid of praja2. Ubiquitin modifications and protein-protein interaction networks were monitored by IP, western blot, mass spectrometry and proteomic analysis. Experiments in vitro and in vivo were performed to define the role of praja2 in RTKs turnover, metabolism, renal cell carcinoma growth and metastatic diffusion. Results: We report here that the ubiquitin ligase praja2 controls endocytosis and the signal strength of different types of receptors (EGFR, VEGFR, TfR). Praja2 forms a complex with- and ubiquitinates the adaptor protein AP2m required for the activity of ATPase and acidification of endosomes and lysosomes necessary for receptor endocytosis and clearance. Downregulation of praja2 blocks the endocytosis of several membrane receptors, including EGFR, VEGFR and TfR and amplifies mitogenic and proliferative signaling as shown in the clear cell renal cell carcinoma (ccRCC). Restoring praja2 expression in RCC cells reduces EGFR levels, rewires cancer cell metabolism and inhibits growth and metastatic diffusion. In vivo, praja2 knockout mice show upregulation of tyrosine kinase receptors (RTKs) and pronounced histopathological renal alterations. Conclusion: Our findings identify praja2 as an important regulator of tyrosine kinase receptor(s) turnover and can be considered a bona fide oncosuppressor because it finely regulates signaling of several types of receptors and its loss supports kidney cancer growth and diffusion.

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Downregulation of RING ligase praja2 boosts receptor tyrosine kinases in kidney cancer

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