The role of tissue transglutaminase in the progression of colorectal cancer

Abstract

There is a significant loss in the efficacy of the current therapeutic regime on advanced colorectal cancer, highlighting the need to understand the tumour progression process, and to identify potential prognostic and/or therapeutic targets. This study employs well characterised human primary and metastatic colorectal cancer cell lines (CRCs); RKO, SW480 SW620, and HCT116 to investigate the involvement of pro-inflammatory protein tissue transglutaminase (TG2) in tumour progression. Cancer progression was assessed by evaluating Epithelial-Mesenchymal Transition (EMT), cancer cell invasion, drug resistance and the ability of CRCs to form spheroid containing cancer stem cells. TG2’s expression was found to correlate with the advancement of the original tumour, markers of EMT, cell invasion, drug resistance, and cancer stemness. Manipulation of TG2 expression in the different CRCs by shRNA or TG2 transduction confirmed the relationship between TG2, EMT, tumour invasion and drug resistance. TGFβ1 was shown to regulate TG2 expression and EMT in primary tumour cell lines by both canonical and non-canonical (RKO and SW480) signalling pathways. TGFβ1 also induced TG2 in the highly advanced HCT116 cells. However, the metastatic SW620 cell line was non-responsive to TGFβ1, but TG2 was associated with the increased presence of nuclear β-catenin in these cells, and TG2’s inhibition/knockdown led to an increased interaction between β-catenin and ubiquitin as determined by co-immunoprecipitation. Interestingly, β-catenin and TG2 were found to be highly expressed in spheroids containing cancer stem-like cells only formed in the aggressive SW620 and HCT116 cell lines. These cancer stem cells were associated with heightened EMT, cellular invasion and angiogenic potential, which was attenuated following TG2 inhibition. TG2 may play a role in tumour progression in human CRCs through its involvement in EMT and the acquisition of cancer stem cell-like properties and may hold both prognostic and therapeutic potentials in colorectal cancer.