Functional analysis of transgelin in breast cancer

Transgelin (TAGLN) is an actin-binding protein. It is highly expressed in fibroblasts and smooth muscle cells. In smooth muscle cells, it takes part in processes including motility and differentiation and also it has a role in the formation of stress fibers. TAGLN gene has been found to be downregulated by promoter hypermethylation in breast and colon tissues and in these tissues, it acted as a tumor suppressor gene. However, in a study on nerve sheath tumors, TAGLN expression was found as upregulated via hypomethylation and in nerve sheath tumors, it acted as a proto-oncogene. To the best of our knowledge, the functional effect of TAGLN gene expression has not been studied in detail in breast carcinoma cell lines. The aim of this study was therefore to identify the functional role of TAGLN in breast cancer development. Hence, TAGLN gene expression was silenced or overexpressed and functional analysis was performed in selected breast cancer cell lines. Breast cancer cell lines were chosen according to their subtypes such as basal, HER2 positive or triple negative; their migratory properties; epithelial or mesenchymal characteristics and the expression level of TAGLN. Therefore, triple negative and mesenchymal MDA-MB-157 cells and MDA-MB-231 cells that express TAGLN at medium level were selected to silence TAGLN expression. The same cell lines and HER2 positive and epithelial MDA-MB-361 cells which express TAGLN at very low level were selected to overexpress TAGLN gene. Immunofluorescence and western blot analysis showed that in MDA-MB-157 and MDA-MB-231 cells mesenchymal marker Vimentin expression is correlated with TAGLN gene expression level. On the contrary, a reverse relationship exists in MDA-MB-361 cells where E-Cadherin expression increased and Vimentin expression decreased in TAGLN overexpressing MDA-MB-361 cells. TAGLN silencing in MDA-MB-157 cells increased the cell spreading potential and viability capacity while TAGLN upregulated cells did not show any significant change. TAGLN silencing in MDA-MB-231 cells decreased the cell spreading potential and cell viability of the cells, TAGLN overexpression in MDA-MB-231 cells increased these properties of cells. MDA-MB-361 cells behaved differently with TAGLN overexpression; cells were able to form less colonies and cell viability decreased in TAGLN overexpressing cells. TAGLN gene silencing affected the cell cycles of MDA-MB-157 and MDA-MB-231 cells but TAGLN overexpression had no effect on the cell cycle. In conclusion, TAGLN expression has an effect on Epithelial to Mesenchymal Transition (EMT) by altering the expression of established EMT markers E-Cadherin and Vimentin and its effect is based on the original morphology of the respective cell lines. In this study, the effect of TAGLN expression on cell proliferation was also studied and TAGLN seems to be acting as a tumor suppressor in MDA-MB-157 and MDA-MB-361 cells and as an oncogene in MDA-MB-231 cells. This might be due to the invasive character of MDA-MB-231 cells and the underlying mechanisms for this outcome should be investigated. Also, in vivo experiments can be performed to see whether changes in the expression of TAGLN gene has a role in tumor formation or metastasis capacity of cells.