Background Oral tongue squamous cell carcinoma (OTSCC) has a 50-55% 5-year survival rate. Cancer stem cells (CSC), the proposed origin of cancer, have been demonstrated in many types of cancer, including OTSCC. We have recently characterised subpopulations of CSCs within moderately differentiated OTSCC (MDOTSCC). We have also shown that these CSCs express components of the renin angiotensin system (RAS), suggesting that CSCs may be a novel therapeutic target by modulation of the RAS. However, enzymes such as cathepsins B, D and G may provide bypass of the RAS, allowing production of angiotensin II despite blocking of upstream RAS components.
Aim This study aimed to investigate the expression and localisation of cathepsins B, D and G in relation to CSC subpopulations within MDOTSCC.
Methods 3,3-Diaminobenzidine (DAB) and immunofluorescent (IF) immunohistochemical (IHC) staining were performed on MDOTSCC samples from six patients to determine the expression and localisation of cathepsins B, D and G. NanoString gene expression analysis and colourimetric in-situ hybridisation (CISH) were used to study their transcripts expression.
Results DAB IHC staining demonstrated expression of cathepsin B, D and G in MDOTSCC. IF IHC staining showed that cathepsins B and D were localised to CSCs within the tumour nests, while cathepsins B, D and G were localised to CSCs within the peri-tumoural stroma. NanoString and CISH analyses confirmed transcription activation of cathepsins B, D and G.
Discussion Cathepsins B, D and G were present in MDOTSCC and were localized to the CSC subpopulations. This suggests the presence of bypass loops for the RAS.
Conclusions The presence of cathepsins B, D and G within CSCs suggest the presence of bypass loops for the RAS. This novel finding may lead to effective control of the CSCs in MDTOSCC by more comprehensive regulation by RAS.