Cancer Stem Cells in Head and Neck Cutaneous Squamous Cell Carcinoma Express Cathepsins

Abstract

Background: Cancer stem cell (CSC) subpopulations within moderately differentiated head and neck cutaneous squamous cell carcinoma (MDHNcSCC) express the components of the renin–angiotensin system (RAS). This study investigated the expression of cathepsins B, D, and G, which constitute bypass loops of the RAS, by CSCs in MDHNcSCC. Methods: Immunohistochemical staining was performed on MDHNcSCC tissue samples from 15 patients to determine the expression of cathepsins B, D, and G. Co-localization of these cathepsins with the embryonic stem cell markers Octamer-binding transcription factor 4 (OCT4) and c-MYC was investigated with immunofluorescence staining. Reverse transcription quantitative polymerase chain reaction was performed on 5 MDHNcSCC tissue samples to investigate transcript expression of cathepsins B, D and G. Western blotting and enzymatic activity assays were performed on 5 MDHNcSCC tissue samples and 6 MDHNcSCC-derived primary cell lines to confirm protein expression, transcript expression, and functional activity of these cathepsins, respectively. Results: Immunohistochemical staining demonstrated the expression of cathepsins B, D, and G in all MDHNcSCC tissue samples. Immunofluorescence staining showed localization of cathepsins B and D to the c-MYC+ CSC subpopulations and the OCT4+ CSC subpopulations within the tumor nests and the peritumoral stroma. Cathepsin G was expressed on the tryptase+/c-MYC+ cells within the peritumoral stroma. Reverse transcription quantitative polymerase chain reaction demonstrated transcript expression of cathepsins B, D and G in the MDHNcSCC tissue samples. Western blotting and enzymatic activity assays confirmed protein expression and functional activity of cathepsins B and D in the MDHNcSCC tissue samples and MDHNcSCC-derived primary cell lines, respectively. Conclusions: Cathepsins B, D, and G are expressed in MDHNcSCC with functionally active cathepsins B and D localizing to the CSC subpopulations, and cathepsin G is expressed by mast cells, suggesting the potential use of cathepsin inhibitors in addition to RAS blockade to target CSCs in MDHNcSCC.

Epithelial-Mesenchymal Transition (EMT): The Type-2 EMT in Wound Healing, Tissue Regeneration and Organ Fibrosis

“…In these studies, trans-differentiation processes that take place during tissue repair, tumorigenesis and organogenesis have been widely explored through three-dimensional (3D) tissue-derived spheroid systems. In contrast with 2D structures, 3D systems mimic patho-physiological processes, allowing cell–cell, cell-matrix and cross-talk interactions [ 91 , 92 , 93 ]. Studies on 3D systems have shown that trans-differentiation processes such as EMT and MET, both of which are involved in regenerative process, can balance stemness of tumoral and non-tumoral cells and promote the differentiation of specific cell phenotypes [ 94 , 95 ].…”

Cathepsins B, D, and G Are Expressed in Metastatic Head and Neck Cutaneous Squamous Cell Carcinoma

“…We have previously demonstrated expression of cathepsins B, and D by CSCs in a number of cancer types ( 34 – 36 ) including primary HNcSCC ( 37 ). In this study, immunofluorescence staining demonstrated localization of cathepsins B and D to the CSCs within both the TNs and the PTS, and cathepsin G on the phenotypic mast cells within the PTS, similar to OTSCC ( 35 ).…”

“…Cathepsins also prevent cell death through modulation of the lysosomal apoptotic pathways and promote cancer cell invasion through upregulation of cell adhesion and migration ( 30 ). Cathepsins B and D are expressed by CSCs in glioblastoma ( 34 ), oral tongue SCC (OTSCC) ( 35 ), metastatic colon adenocarcinoma to the liver ( 36 ) and primary HNcSCC ( 37 ).…”

Cancer Metastasis and Treatment Resistance: Mechanistic Insights and Therapeutic Targeting of Cancer Stem Cells and the Tumor Microenvironment

“…These alternative signaling pathways enable the RAS to evade single-point inhibitions by traditional RAS inhibitors (RASIs) [ 120 ]. Expression of cathepsins B, D and G has been demonstrated in numerous cancer types including glioblastoma [ 121 ], head and neck SCC [ 122 , 123 ], malignant melanoma [ 124 ], oral tongue SCC [ 125 ], and liver metastasis from colorectal cancer [ 126 ]. Similar to the expression of components of the RAS within these cancer types, cathepsins B and D are expressed on the phenotypic CSC population, while cathepsin G is expressed by phenotypic mast cells.…”