Involvement of BMP and Wnt Signals Leadingto Epithelial-Mesenchymal Transition in Colon Adenocarcinoma with Heterotopic Ossification

Abstract

Here we present the case of a 73-year-old male with rectal adenocarcinoma with heterotopic ossification (HO). Cancer-associated HO in the digestive system is rare. Thus, the precise mechanism and clinicopathological significance of HO have not yet been defined. To clarify the molecular mechanisms of HO, we analyzed the expression levels of signaling molecules related to epithelial-mesenchymal transition (EMT) that lead to ossification in the tumor cells discriminating the ossified area (HO-area) and non-ossified area (non-HO area). Expression levels of BMP4 were elevated in both areas, whereas BMP2 was specifically increased in the HO-area by qPCR. EMT-related molecules such as Snail and Slug were especially higher in the HO-area. By immunohistochemistry, the expression of Smad4, nuclear staining of β-catenin, and the phosphorylated form of GSK-3β were detectable in both areas, and GSK-3β was highly phosphorylated in the HO-area. The tumor growth rate was extremely high, with the Ki-67 labeling index at 90%. In the HO-area, osteoblasts with alkaline phosphatase expression were distributed surrounding the tumor cells. This is the first demonstration of the involvement of EMT in HO of colon cancer through BMP/SMAD and WNT/β-catenin signaling pathways, which are especially prominent in the HO-area leading to the osteogenic property.

Keywords: BMP; EMT; Smad4; heterotopic ossification; β-catenin.