T-box transcription factor 5 (TBX5) is a member of a phylogenetically conserved family of genes involved in the regulation of developmental processes. The function of TBX5 in
cancer development is largely unclear. We identified that TBX5 was preferentially methylated in
cancer using methylation-sensitive arbitrarily primed PCR. We aim to clarify the epigenetic inactivation,
biological function and clinical significance of TBX5 in
colon cancer. Promoter methylation was evaluated by combined
bisulfite restriction analysis and
bisulfite genomic sequencing. Cell proliferation was examined by cell viability assay and colony formation assay, apoptosis by flow cytometry and cell migration by wound-healing assay. TBX5 target genes were identified by
cDNA microarray analysis. Cox regression model and log-rank test were used to identify independent predictors of prognosis. TBX5 was silenced or downregulated in 88% (7/8)
colon cancer cell lines, but was expressed in normal colon tissues. Loss of gene expression was associated with promoter methylation. The
biological function of TBX5 in human
colon cancer cells was examined. Re-expression of TBX5 in silenced
colon cancer cell lines suppressed colony formation (P<0.001), proliferation (P<0.001), migration and induced apoptosis (P<0.01). Induction of apoptosis was mediated through cross-talk of extrinsic apoptosis pathway, apoptotic
BCL2-associated X protein and
Granzyme A signaling cascades. TBX5 suppressed
tumor cell proliferation and
metastasis through the upregulation of
cyclin-dependent kinase inhibitor 2A,
metastasis suppressor 1 and downregulation of
synuclein gamma and
metastasis-associated
protein 1 family member 2. TBX5 methylation was detected in 68% (71/105) of primary colon
tumors. Multivariate analysis showed that patients with TBX5 methylation had a significantly poor overall survival (P=0.0007). In conclusion, we identified a novel functional tumor suppressor gene TBX5 inactivated by promoter methylation in
colon cancer. Detection of methylated TBX5 may serve as a potential
biomarker for the prognosis of this
malignancy.