Mutation of P81 proline to a serine alters the tumor suppressor function of the von Hippel-Lindau gene in ccRCC.

The vhl gene is a tumor suppressor whose mutations or inactivation cause Von Hippel-Lindau syndrome, an autosomal dominant inherited disorder. These events result in a high susceptibility to develop certain cancers including clear cell renal cell carcinomas (ccRCC). ccRCC represent 70 to 80% of renal cancers; they appear late, cause many deaths in France and represent the main cause of mortality in patients with vhl disease. The high mutation rate of the VHL gene and/or the lack of expression of the protein play(s) a crucial role in tumor initiation by causing the loss of functions of the pVHL protein (pVHL213) in epithelial cells, defining VHL as a tumor suppressor gene for ccRCC.

The complexity of the vhl gene located on the short arm of human chromosome 3 (3p25.3 ) lies in part in the fact that it encodes a 213 amino acid protein. Through the use of an internal initiation site or alternative splicing, other shorter isoforms can be generated. The pVHL213 protein is a component of the E3 ligase complex that regulates the level of the transcription factor HIFα (hypoxia inducible factor -α). pVHL also regulates cellular functions independently of its activity on HIF; for example, VHL participates in extracellular matrix restructuring, microtubule organization, migration, and cell invasion. Several independent studies have shown that pVHL213 is involved in cell polarity, proliferation and the cell cycle.

Of the 1,230 mutations listed in the VHL database (http://umd.be/VHL), many have not yet been functionally characterized. In the British J. Can. article, the authors looked at a family with two members who had clinical symptoms of VHL disease. One of the members developed ccRCC at the age of 37 years and has a germline c.241C>T (P81S) mutation. Genetic study of the offspring revealed the presence of this same mutation in the children (Fig A).

A structural (Fig B), biochemical and cellular (Fig C) study of the mutated protein shows a structural transformation and an assignment of non-canonical functions of the protein associated with cellular morphological changes that give the cells an invasive character.

A - Description of the pedigree of the family that is affected by the P81S mutation. 
Pedigree of the family A- ccRCC : clear cell renal cell carcinoma, BC : breast cancer

+ : carrier of the germline mutation c.241C>T, p.Pro81Ser in the vhl gene
- : not carrying the germline c.241C>T, p.Pro81Ser in the vhl gene

 

B - Structural organization of the different domains of pVHL213

 

 

C - Tumorigenic effect of pVHL213-P81S in 786-O cells
The spheroids obtained from the 3 different cell lines were deposited in Matrigel. The morphology of the spheroids was recorded after 24 hours of culture.