Loss of SUFU function in familial multiple meningioma

Abstract

Meningiomas are the most common primary tumors of the CNS and account for up to 30% of all CNS tumors. An increased risk of meningiomas has been associated with certain tumor-susceptibility syndromes, especially neurofibromatosis type II, but no gene defects predisposing to isolated familial meningiomas have thus far been identified. Here, we report on a family of five meningioma-affected siblings, four of whom have multiple tumors. No NF2 mutations were identified in the germline or tumors. We combined genome-wide linkage analysis and exome sequencing, and we identified in suppressor of fused homolog (Drosophila), SUFU, a c.367C>T (p.Arg123Cys) mutation segregating with the meningiomas in the family. The variation was not present in healthy controls, and all seven meningiomas analyzed displayed loss of the wild-type allele according to the classic two-hit model for tumor-suppressor genes. In silico modeling predicted the variant to affect the tertiary structure of the protein, and functional analyses showed that the activity of the altered SUFU was significantly reduced and therefore led to dysregulated hedgehog (Hh) signaling. SUFU is a known tumor-suppressor gene previously associated with childhood medulloblastoma predisposition. Our genetic and functional analyses indicate that germline mutations in SUFU also predispose to meningiomas, particularly to multiple meningiomas. It is possible that other genic mutations resulting in aberrant activation of the Hh pathway might underlie meningioma predisposition in families with an unknown etiology.

Figure 1

Pedigree of Family 1 with Five Siblings with Intracranial Meningiomas The ages at meningioma operations and the c.367C>T (p.Arg123Cys) SUFU mutation status of the individuals are shown. A plus sign denotes a mutation, and a minus sign denotes a wild-type allele. The pedigree has been slightly modified for confidentiality.

Figure 2

Loss of Heterozygosity and In Silico Modeling of the SUFU Mutation (A) Heterozygous germline SUFU mutation c.367C>T (p.Arg123Cys) and loss of heterozygosity in a meningioma tumor tissue. The site of the mutation is indicated by an arrow. (B–D) Surface representation of the N-terminal part of SUFU modeled in COOT. (B) Cartoon of the secondary structure. The N- and C-terminal subdomains are marked, and Arg123 is represented by a ball-and-stick model. (C) Ribbon representation of the wild-type N-terminal part of SUFU. Secondary structure elements are labeled in accordance with Merchant et al. Arg123 and residues involved in interactions are represented by ball-and-stick models. Dashed lines represent hydrogen bonds and ionic contacts. (D) The same orientation for the p.Arg123Cys altered SUFU. All contacts formed by Arg123 disappear, and loops are connected rather weakly.

Figure 3

The Effect of the p.Arg123Cys Altered SUFU on Hedgehog Signaling Activity (A and B) The p.Arg123Cys altered SUFU has decreased activity. Human rhabdomyosarcoma cells (CRL-2061) and Sufu-deficient (Sufu^−/−) MEFs were transfected with Myc-tagged wild-type (Myc-SUFUWT) or altered (Myc-SUFUp.Arg123Cys) SUFU constructs, an Hh-pathway-specific reporter, and a control reporter. The cells were incubated with and without ShhN-conditioned medium, and luciferase activity was measured. Note that Myc-SUFU suppresses Hh-pathway activity in both human and mouse cell lines. ^∗p < 0.05 compared with Myc-hSUFUWT (statistical analysis was done with a t test). Error bars indicate one standard deviation (duplicate samples). (C) The p.Arg123Cys altered SUFU binds less GLI1 than does the wild-type SUFU. CRL-2061 cell lysates used in luciferase reporter assay were subjected to pull-down immunoblot analysis (IP: GLI1; WB: Myc and GLI1). In the top panel, Myc-SUFU is pulled down with antibodies against GLI1. Input of GLI1 and Myc-tagged SUFU constructs is presented in the middle and bottom panels, respectively. Quantification of GLI1 binding relative to the Myc-SUFU protein level is shown below the panel (quantitative protein analysis was performed with the Single Dimensional Electrophoretic Gel Analysis program from the ImageJ software package v.1.46g). (D) Subcellular localization of p.Arg123Cys altered SUFU in Sufu^−/− MEFs. Note that the Gli1 nuclear localization was not affected by the human SUFU mutant (Myc-SUFUp.Arg123Cys) compared with the wild-type SUFU (Myc-SUFUWT), as indicated by arrows.