The VHL-dependent regulation of microRNAs in renal cancer.
BACKGROUND
The commonest histological type of renal cancer, clear cell renal cell carcinoma (cc RCC), is associated with genetic and epigenetic changes in the von Hippel-Lindau (VHL) tumour suppressor. VHL inactivation leads to induction of hypoxia-inducible factors (HIFs) and a hypoxic pattern of gene expression. Differential levels of specific microRNAs (miRNAs) are observed in several tumours when compared to normal tissue. Given the central role of VHL in renal cancer formation, we examined the VHL-dependent regulation of miRNAs in renal cancer.


METHODS
VHL-dependent miRNA expression in cc RCC was determined by microarray analysis of renal cell line RCC4 with mutated VHL (RCC4-VHL) and reintroduced wild-type VHL (RCC4 + VHL). Five miRNAs highly upregulated in RCC4 + VHL and five miRNAs highly downregulated in RCC4 + VHL were studied further, in addition to miR-210, which is regulated by the HIF-VHL system. miRNA expression was also measured in 31 cc RCC tumours compared to adjacent normal tissue.


RESULTS
A significant increase in miR-210, miR-155 and miR-21 expression was observed in the tumour tissue. miR-210 levels also showed a correlation with a HIF-regulated mRNA, carbonic anhydrase IX (CAIX), and with VHL mutation or promoter methylation. An inverse correlation was observed between miR-210 expression and patient survival, and a putative target of miR-210, iron-sulfur cluster assembly protein (ISCU1/2), shows reciprocal levels of mRNA expression in the tumours.


CONCLUSIONS
We have identified VHL-regulated miRNAs and found that for some the regulation is HIF-dependent and for others it is HIF-independent. This pattern of regulation was also seen in renal cancer tissue for several of these miRNAs (miR-210, miR-155, let-7i and members of the miR-17-92 cluster) when compared with normal tissue. miR-210 showed marked increases in expression in renal cancer and levels correlated with patient survival. The inverse correlation between miR-210 levels and ISCU1/2 provides support for the hypothesis that ISCU1/2 is a target of miR-210 and that it may contribute to the anaerobic respiration seen in renal (and other) tumours.See Commentary: http://www.biomedcentral.com/1741-7015/8/65.
Renal Unit, School of Medicine, Flinders University, Flinders Medical Centre, Adelaide, Australia.
Calida S
CS
Neal
Michael Z
MZ
Michael
Lesley H
LH
Rawlings
Mark B
MB
Van der Hoek
Jonathan M
JM
Gleadle
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000951:Antigens, Neoplasm / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases / Q000378:metabolism; D002292:Carcinoma, Renal Cell / Q000235:genetics* / Q000378:metabolism / Q000401:mortality; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D005260:Female; D015870:Gene Expression / Q000235:genetics; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000235:genetics; D053208:Kaplan-Meier Estimate; D007680:Kidney Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000401:mortality; D008297:Male; D035683:MicroRNAs / Q000378:metabolism*; D046228:Microarray Analysis; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D018709:Statistics, Nonparametric; D014407:Tumor Cells, Cultured; D051794:Von Hippel-Lindau Tumor Suppressor Protein / Q000235:genetics*; D000099162:Endothelial PAS Domain-Containing Protein 1
D000951:Antigens, Neoplasm; D051792:Basic Helix-Loop-Helix Proteins; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007506:Iron-Sulfur Proteins; D035683:MicroRNAs; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D000099162:Endothelial PAS Domain-Containing Protein 1; C506160:ISCU protein, human; C524942:MIRN155 microRNA, human; C543800:MIRN210 microRNA, human; C487931:mirnlet7 microRNA, human; C089226:CA9 protein, human; C497446:VHL protein, human