Combined Deletion of Vhl and Kif3a Accelerates Renal Cyst Formation

Abstract

A subset of familial and sporadic clear cell renal cell carcinomas (ccRCCs) is believed to develop from cystic precursor lesions. Loss of function of the von Hippel-Lindau tumor suppressor gene (VHL) predisposes renal epithelial cells to loss of the primary cilium in response to specific signals. Because the primary cilium suppresses renal cyst formation, loss of the cilium may be an initiating event in the formation of ccRCC. To test this hypothesis, we analyzed the consequences of inducible renal epithelium-specific deletion of Vhl together with ablation of the primary cilium via deletion of the kinesin family member 3A (Kif3a) gene. We developed a microcomputed tomography-based imaging approach to allow quantitative longitudinal monitoring of cystic burden, revealing that combined loss of Vhl and Kif3a shortened the latency of cyst initiation, increased the number of cysts per kidney, and increased the total cystic burden. In contrast with findings in other cystic models, cysts in Kif3a mutant mice did not display accumulation of hypoxia-inducible factor 1-a (HIF1a), and deletion of both Hif1a and Kif3a did not affect cyst development or progression. Vhl/Kif3a double mutation also increased the frequency of cysts that displayed multilayered epithelial growth, which correlated with an increased frequency of misoriented cystic epithelial cell divisions. These results argue against the involvement of HIF1a in promoting renal cyst growth and suggest that the formation of simple and atypical renal cysts that resemble ccRCC precursor lesions is greatly accelerated by the combined loss of Vhl and the primary cilium.

MYC activation cooperates with Vhl and Ink4a/Arf loss to induce clear cell renal cell carcinoma

“…Multiple groups have now demonstrated that Vhl inactivation either in the germline or by conditional inactivation in the kidney results in only a mild increase in rate of renal cyst formation2638394041. While the addition of secondary genetic events such as Pten or Kif3a loss appear to accelerate the cystic phenotype induced by Vhl inactivation, they do not result in frank neoplasia4243. Combined inactivation of Vhl with Trp53 does appear to induce renal tumours, which have clear cell changes but not bona fide clear cell RCC histology44.…”

Formation of Renal Cysts and Tumors in Vhl/Trp53-Deficient Mice Requires HIF1α and HIF2α

“…5) argues that ccRCC formation requires mutations in addition to VHL. There are currently no autochthonous mouse models that fully reproduce all of the characteristic morphologic and invasive properties of human ccRCC; however, consistent with the hypothesis that multiple cooperating mutations are required for ccRCC development, kidney epithelial cell-specific codeletion of Vhl with Pten (6), or with Kif3a to genetically ablate primary cilia (7), caused the formation of simple and atypical cystic lesions that are similar to the ccRCC precursor cystic lesions found in the kidneys of patients with inherited VHL disease. Deletion of Vhl together with homozygous loss of Trp53 (8) or with heterozygous loss of Bap1 (9) gave rise to very similar phenotypes, including simple and atypical cystic lesions as well as tumors containing cells that display cytoplasmic clearing and elevated mTORC1 activity, recapitulating many of the cellular and molecular changes that are characteristic of human ccRCC.…”

HIF Stabilization Weakens Primary Cilia

“…Ciliogenesis is regulated by pVHL [16], pVHL and glycogen synthase kinase-3β (GSK3β) together regulate cilium maintenance [17], and pVHL has been shown to act as a microtubule stabilizer [18]. Even so, it remains unclear if these functions of pVHL are HIF-regulation independent, as recent knockout experiments have shown that HIF-1α is not involved in renal cyst growth [19]. Regarding potential direct interactions between HIF and cilia, recent results show that prolyl hydroxylase inhibition of HIF-2α leads to HIF-2α accumulation within the cilia [20] and deubiquintination of HIF-1α is essential for ciliogenesis [21].…”