Etude de pVHL172, une isoforme du suppresseur de tumeur Von Hippel Lindau : implication dans la tumorigenèse rénale
Pauline HASCOËT - Bases Moléculaires de la tumorigenèse: Maladies de VHL, IGDR (Rennes, France)
- Olivier COQUERET - Professeur - Université d'Angers - Reporter
- Odile FILHOL-COCHET - Chargée de Recherche INSERM - Université de Grenoble - Reporter
- Jean-Jacques PATARD - Professeur des Universités, Praticien Hospitalier - CHU Bicêtre - Examiner
- Nathalie THERET : Directrice de Recherche INSERM, Université de Rennes I - Examiner
- Xavier LE GOFF - Chargé de Recherche CNRS, Université de Rennes I - Director
- Franck CHESNEL - Chargé de Recherche CNRS, Université de Rennes I - Co-director
VHL disease predisposes to the development of multiple and highly vascularized tumors, including central nervous system and retinal haemangioblastomas, phaeochromocytomas and clear cell renal cell carcinomas (ccRCCs). Patients with VHL disease harbor a mutant allele of the VHL gene. This gene is transcribed into two mRNAs by alternative splicing of the exon 2. The mRNA variant #1 composed of 3 exons usually predominates over the mRNA variant #2 lacking exon 2. A decrease of the variant #1/variant #2 ratio was however described in 2 situations: (i) in embryonic tissues, particularly in the kidney, and (ii) in some ccRCCs. These data suggest a potential role for the variant #2 in kidney tumorigenesis. pVHL213 and pVHL160 are the two proteins encoded by the mRNA variant #1 and act as tumor suppressors. At the beginning of this Ph.D. project, the expression of pVHL172 isoform encoded by the mRNA variant #2 remained to be established and its function was unknown.
The experiments performed during this Ph.D. shed light on pVHL172 expression in cell lines and in tumor tissues using a newly produced mouse monoclonal antibody recognizing the three human pVHL isoforms. To examine if pVHL172 had a tumor suppressor function, human kidney tumor cell lines stably expressing this isoform were established, characterized and then grafted in mice. pVHL172 not only inhibits tumor formation, but its expression also induces a more aggressive phenotype with a higher sarcomatoid component and a more immature vasculature compared to control tumors (that do not express any pVHL). Moreover, pVHL172 increases the matrix metalloproteases MMP1 and MMP13 expression, partly by the activation of the Smad-dependent TGF-β signalling pathway. Besides, we looked for protein partners of pVHL172 by a differential proteomic analysis and showed that interaction networks obtained with the identified proteins are related to extracellular matrix regulation and protein quality control.
To conclude, this work demonstrated that the VHL gene encodes protein isoforms with distinct and even antagonistic functions. The balance of expression of these isoforms is likely to influence kidney tumor progression. For some patients, an increase of pVHL172 expression could be correlated with a more severe pathology. This work shows the importance of further studying this isoform’s functions to better understand its involvement in kidney cancer and in VHL disease, so that new therapeutic approaches could be developed.
>> Wednesday, April 27 at 14:30 - Amphitheater D (Faculty of Medicine, Building 2 / Villejean Campus / Rennes)
PhD defense in French