The SFRP family of WNT inhibitors function as novel tumor suppressor genes epigenetically silenced in medulloblastoma

Abstract

Medulloblastoma (MB) is the most common malignant pediatric brain tumor. Dysregulation of WNT signaling occurs in up to 20% of cases. Using a genome-wide approach, we identified the secreted frizzled-related protein 1, 2 and 3 (SFRP1, SFRP2 and SFRP3) family of WNT inhibitors as putative tumor suppressor genes silenced by promoter region methylation in MB. SFRP1, SFRP2 and SFRP3 expression increased after 5-aza-2 0 -deoxycytidine treatment. SFRP1, SFRP2 and SFRP3 methylation was identified in 23.5, 3.9 and 15.7% of primary MB specimens, respectively, by methylationspecific PCR. Stable SFRP1, SFRP2 and SFRP3 expression reduced phospho-DVL2 levels and hindered MB cell proliferation and colony formation in soft agar in vitro. In 60% of primary tumors, SFRP1 was expressed at levels twofold lower than that in normal cerebellum. SFRP1 expression impaired tumor formation in vivo in flank and orthotopic intracerebellar xenograft models and conferred a significant survival advantage (Po0.0001). We identify for the first time tumor suppressor gene function of SFRP genes in MB, and suggest that loss of WNT pathway inhibition due to SFRP gene silencing is an additional mechanism that may contribute to excessive WNT signaling in this disease.

Secreted Frizzled-related protein 2 as a target in antifibrotic therapeutic intervention

“…Alternatively, activation of MMPs after sFRP2 blockade or MSC therapy may release VEGF and HGF from the ECM niche as demonstrated for basic fibroblast growth factor by Whitelock et al (63). This VEGF-antagonizing effect of sFRP2 appears in line with the emerging notion that sFRP2 may represent a novel tumor-suppressor gene, the expression of which is often silenced in cancer cells (29). Saline Control sFRP2 antibody A B Fig.…”

Epigenetic mechanisms regulating neural development and pediatric brain tumor formation

“…109 Germline mutations in the adenomatous polyposis coli (APC) gene cause Turcot syndrome and more rarely sporadic medulloblastoma. 58 Using an epigenetic genome-wide approach, Kongkham et al 72 identified a group of Wnt inhibitors-the secreted frizzled-related protein family (SFRP1, SFRP2, and SFRP3)-that function as tumor suppressor genes and are silenced by promotor methylation in medulloblastoma. Secreted frizzled-related protein expression reduced cell proliferation and anchorage-independent growth in vitro and impaired tumor formation in vivo.…”

High expression of DNA methyltransferases in primary human medulloblastoma

“…The SHH pathway was inhibited in pancreatic cancer and MDS cell lines, resulting in decreased DNMT1 expression, whereas induction of the SHH pathway resulted in higher DNMT1 expression [16,40]. In contrast, DNMT1 inhibition resulted in increased expression of SFRP1 in MB cell lines [20]. One explanation could be that investigated MB cell lines do not belong to the SHH subgroup, since they showed lower levels of SFRP1 compared to the SHH subgroup.…”