C4.4A is a glycolipid‐anchored membrane protein expressed in several human malignancies. The aim of this study was to explore the association between C4.4A expression at the invasion front of colorectal cancer (CRC) and tumor budding, a putative hallmark of cell invasion of CRC. Advanced CRCs (T2–4, n = 126) had a budding count of 3.66 ± 5.66, which was significantly higher than that of T1 early CRCs (1.75 ± 2.78, n = 87). C4.4A‐positive CRC specimens showed a larger budding cell number than C4.4A‐negative CRC specimens in T1 CRCs, and especially advanced CRCs (9.45 ± 5.83 vs 1.60 ± 3.93). Furthermore, we found a correlation between the percentage of C4.4A‐positive cases and budding count in advanced CRC. Multivariate analysis for patients' survival showed that C4.4A was superior to tumor budding as a prognostic factor. With siRNA treatment, C4.4A levels were associated with cell invasion, but not with proliferation, in HCT116 and DLD1 cell lines. An immunohistochemical study in a subset of CRCs showed no relationship between C4.4A and Ki‐67 proliferation marker. In vitro assays using HCT116 indicated that C4.4A levels correlated well with epithelial–mesenchymal transition (EMT) with regard to cell morphology and alterations of EMT markers including E‐cadherin, vimentin, and partially N‐cadherin. We also found that C4.4A expression was significantly associated with loss of E‐cadherin and gain of β‐catenin in clinical CRC tissue samples. These findings suggest that a tight association between C4.4A and tumor budding may, in part, be due to C4.4A promoting EMT at the invasive front of CRC. (Cancer Sci 2012; 103: 1155–1164)
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