Differences in regulation of tight junctions and cell morphology between VHL mutations from disease subtypes.
BACKGROUND
In von Hippel-Lindau (VHL) disease, germline mutations in the VHL tumor suppressor gene cause clear cell renal carcinomas, hemangioblastomas, and pheochromocytomas. The VHL gene product is part of an ubiquitin E3 ligase complex and hypoxia-inducible factor alpha (HIF-alpha) is a key substrate, although additional VHL functions have been described. A genotype-phenotype relationship exists in VHL disease such that specific VHL mutations elicit certain subsets of these tumors. Here, we examine VHL genotype-phenotype correlations at the cellular level, focusing on the regulation of tight junctions and cell morphology.


METHODS
Wild-type and various mutant VHL proteins representing VHL disease subtypes were stably expressed in 3 VHL-negative renal carcinoma cell lines. Using these cell lines, the roles of various VHL-associated cellular functions in regulation of cell morphology were investigated.


RESULTS
As a whole, type 1 mutants varied greatly from type 2 mutants, demonstrating high levels of HIF-2alpha, cyclin D1 and alpha5 integrin, lower p27 levels, and a spindly, fibroblastic cellular appearance. Type 2 mutations demonstrated an epithelial morphology similar to wild-type VHL in the majority of the renal cell lines used. Knockdown of p27 in cells with wild-type VHL led to perturbations of both epithelial morphology and ZO-1 localization to tight junctions. ZO-1 localization correlated well with VHL disease subtypes, with greater mislocalization observed for genotypes associated with a higher risk of renal carcinoma. HIF-2alpha knockdown in 786-O partially restored ZO-1 localization, but did not restore an epithelial morphology.


CONCLUSIONS
VHL has both HIF-alpha dependent and HIF-alpha independent functions in regulating tight junctions and cell morphology that likely impact the clinical phenotypes seen in VHL disease.
Bangiyeva
Valentina
V
Department of Biology, Adelphi University, Garden City, NY 11530-0701, USA. vbangiyeva@yahoo.com
Rosenbloom
Ava
A
Alexander
Ashlynn E
AE
Isanova
Bella
B
Popko
Timothy
T
Schoenfeld
Alan R
AR
D002277:Carcinoma / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D005786:Gene Expression Regulation; D005838:Genotype; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis / Q000235:genetics*; D007680:Kidney Neoplasms / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D009154:Mutation; D010641:Phenotype; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D019108:Tight Junctions / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D051794:Von Hippel-Lindau Tumor Suppressor Protein / Q000235:genetics*
D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011500:Protein Synthesis Inhibitors; D025801:Ubiquitin; D003513:Cycloheximide; D051794:Von Hippel-Lindau Tumor Suppressor Protein; C497446:VHL protein, human