The Wnt Antagonist sFRP1 in Colorectal Tumorigenesis

Abstract

Regions of the short arm of chromosome 8 are deleted frequently in a range of solid tumors, indicating that tumor suppressor genes reside at these loci. In this study, we have examined the properties of the Wnt signaling antagonist secreted frizzled-related protein (sFRP) 1 as a candidate for this role at c8p11.2. An initial survey of 10 colorectal tumors, selected by the presence of isolated short deletions of the 8p11.2 region, identified three chain-terminating mutations, all within the first exon, which encodes the cysteine-rich domain. None of these tumors exhibited microsatellite instability, indicating intact mismatch repair gene function. The preserved sFRP1 alleles in the remaining seven tumors each contained a polymorphic three-base insertion in the signal sequence, but in a broader study, no association was found between this and the development of colorectal cancer. Epigenetic inhibition of sFRP1 transcription was investigated, and increased methylation of the promotor region was demonstrated in an additional cohort of 51 locally advanced colorectal cancers. Hypermethylation was identified in 40 of 49 (82%) cancers and in only 11 of 36 (30%) matched normal mucosal samples (P < 0.001). Semiquantitative analysis, by real-time PCR, of mRNA expression in 37 of the same cohort of 51 cancers revealed that sFRP1 mRNA expression was down-regulated in 28 (76%) cases compared with matched normal large bowel mucosa. The 3 end of the sFRP1 mRNA also was found to be alternatively spliced, compared with the prototype liver and lung forms, in the colon and a number of other tissues, yielding an extended COOH terminus, which may influence its activity in a tissue-specific manner. The inactivation and down-regulation of sFRP1 observed are consistent with it acting as a tumor suppressor gene in colorectal carcinogenesis. Because ␤-catenin is constitutively active in the majority of colorectal tumors, it is unlikely that sFRP1 can act in the canonical Wnt response pathway. Therefore, we propose that the reduced activity or absence of sFRP1 allows the transduction of noncanonical Wnt signals, which contribute to tumor progression.

Frizzled-7 dictates three-dimensional organization of colorectal cancer cell carcinoids

“…A role for the upstream components of the pathway in CRC, despite mutations in down-stream components (e.g. APC), is clearly supported by recent studies that implicate tumour suppressor roles for naturally occurring inhibitors of the pathway, sFRP and DKK (Caldwell et al, 2004;Suzuki et al, 2004;Aguilera et al, 2006). Importantly, we provide a molecular mechanism for MET in CRC, which we propose is the critical step to metastasis (Brabletz et al, 2001(Brabletz et al, , 2005Vincan, 2004).…”

Frequent epigenetic inactivation of SFRP genes and constitutive activation of Wnt signaling in gastric cancer

“…In addition, we and others recently showed that SFRP family genes are frequent targets of aberrant DNA methylation in CRCs (Suzuki et al, 2002;Caldwell et al, 2004), and we further showed that restoration of SFRP1, SFRP2 and SFRP5 in CRC cells attenuates Wnt signaling, even in the presence of downstream mutations . Since then, downregulation and methylation of SFRP genes have been identified in a variety of malignancies, including bladder cancer (Stoehr et al, 2004), prostate cancer (Lodygin et al, 2005), endometrial cancer (Risinger et al, 2005), lung cancer (Fukui et al, 2005), breast cancer (Veeck et al, 2006), mesothelioma (Lee et al, 2004) and chronic lymphocytic leukemia (Liu et al, 2006), which strongly suggests SFRPs function as tumor suppressor genes.…”

Blocking Wnt signaling by SFRP-like molecules inhibits in vivo cell proliferation and tumor growth in cells carrying active β-catenin

“…It has been suggested that SFRPs may function as tumor suppressors in CRC because allelic loss or epigenetic inactivation of SFRP genes contributes to constitutive activation of the Wnt/b-catenin pathway (Caldwell et al, 2004;Suzuki et al, 2004). In this context, we and others have shown that restoring expression of SFRP-1 or SFRP-5 inhibits Wnt/b-catenin stabilization and induces in vitro cell death in human CRC cells (Suzuki et al, 2004;Quelard et al, 2008).…”