The aberrant methylation of TSP1 suppresses TGF‐β1 activation in colorectal cancer

Abstract

Colorectal cancer arises from the progressive accumulation of mutations and epigenetic alterations in colon epithelial cells. Such alterations often deregulate signaling pathways that affect the formation of colon cancer, such as the Wnt, RAS-MAPK and TGF-b pathways. The tumor promoting effects of mutations in genes, such as APC, have been demonstrated in cancer cell lines and in mouse models of intestinal cancer; however, the biological effects of most epigenetic events identified in colorectal cancer remain unknown. Consequently, we assessed whether the aberrant methylation of TSP1, the gene for thrombospondin 1, a regulator of TGF-b ligand activation, is an epigenetic mechanism for inhibiting the TGF-b signaling pathway. We found methylated TSP1 occurs in colon cancer cell lines (33%), colon adenomas (14%) and colon adenocarcinomas (21%). In primary colorectal cancers, loss of TSP1 expression correlated with impaired TGF-b signaling as indicated by decreased Smad2 phosphorylation and nuclear localization. Furthermore, methylation-induced silencing of TSP1 expression reduced the concentration of secreted active TGF-b1 and attenuated TGF-b signaling. Reversal of TSP1 methylation resulted in increased TSP1 mediated activation of the latent LAP:TGF-b complex and subsequent TGF-b receptor activation. Our results demonstrate that the aberrant methylation of TSP1 has biological consequences and provide evidence that the aberrant methylation of TSP1 is a novel epigenetic mechanism for suppressing TGF-b signaling in colorectal cancer. ' 2008 Wiley-Liss, Inc.Key words: thrombospondin; transforming growth factor b; methylation; colorectal cancer; epigenetics Colorectal cancer is the third most common cancer in the United States. In 2008, 154,000 new cases of colorectal cancer will be diagnosed and more than 52,000 people are predicted to die from the disease. 1 Colon cancer arises from the accumulation of DNA alterations in colon epithelial cells, which mediate the initiation and progression of this cancer. Mutations in genes such as KRAS, TP53 and members of the transforming growth factor (TGF-b) signaling pathway play a pathogenic role in the polypcarcinoma sequence. [2][3][4] TGF-b is a pluripotent cytokine that has a multitude of effects on epithelial cells including the inhibition of proliferation, the induction of apoptosis and the stimulation of differentiation. Inactivating mutations in central members of the TGF-b signaling pathway, TGFBR2 and SMAD4, have been identified in approximately half of colon cancers. [5][6][7][8] The biological effects of TGF-b in the colon and the identification of inactivating mutations in TGFBR2 and SMAD4 in colon cancers have demonstrated that the TGF-b signaling pathway can act as a colon cancer tumor suppressor pathway.The TGF-b signaling pathway consists of the TGF-b ligand; the heteromeric TGF-b receptor composed of the type I and type II TGF-b receptors (TGFBR1 and TGFBR2); and the post-receptor signaling proteins, including SMAD2, 3, and 4. TGF-b1 is the most commonly expre...

Association Between Thrombospondin-1, Angiogenesis Related Markers, and Extracellular Matrix Components with Colorectal Cancer Outcome

“…Tumors from patients that expressed high levels of TSP-1 and had low MVD counts were more likely to exhibit a decrease in angiogenesis compared to control tissue. The inverse has also been documented; a decrease in TSP-1 expression was accompanied with high MVD counts which may contribute to an angiogenic phenotype [31,39,40]. In the present study, we failed to demonstrate any correlation between TSP-1 expression, MVD and VEGF expression.…”

“…These results may be due to the difference in TSP-1 products produced by tumor cells or to different antibodies used. Rojas et al, suggested that the tumor cells are a major source of TSP-1 and that methylation of TSP-1 substantially reduces TSP-1 activity in the tumors of the colon [39].…”

“…Clinical studies of patients with CRC have investigated levels of TSP-1 and correlated it with angiogenesis [14,15,39]. This relationship was established based on a significant association between TSP-1 expression, VEGF expression and MVD count.…”

BAMBI gene is epigenetically silenced in subset of high‐grade bladder cancer

“…8,12,13 In colorectal cancers, for example, where the TGF-b/BMP signaling pathway in general negatively regulates tumor cell proliferation from early carcinogenesis to a later progression stage, loss-of-function mutation in TGF-b/BMP signaling, such as the inactivating mutation of SMAD4, has frequently been identified as an important early carcinogenic event. 10,14,15 On the other hand, in various types of cancers especially at later cancer progression stages, TGF-b/BMPs, frequently produced by cancer cells themselves, promote angiogenesis and epithelial-to-mesenchymal transition (EMT). Furthermore, in a certain subset of aggressive cancers, the TGF-b/BMP signaling pathway often promotes cancer cell invasion and migration in an autocrine and paracrine manner.…”

Pharmaco-epigenomics: discovering therapeutic approaches and biomarkers for cancer therapy

“…Glioblastomas, for instance, are typically characterized by excessive blood vessel development and frequently display epigenetic inactivation of the anti-angiogenic thrombospondin-1 (THBS-1) gene (Li et al, 1999). THBS-1 is also suppressed early in breast carcinogenesis by histone modifications (Hinshelwood et al, 2007) and THBS-1 silencing through methylation is observed in a significant portion of primary colorectal adenomas (Rojas et al, 2008). Interestingly, oxygen-glucose deprivation, which frequently occurs in tumors, was shown to increase THBS-1 promoter methylation and subsequent silencing.…”