ADAM17‐mediated CD44 cleavage promotes orasphere formation or stemness and tumorigenesis in HNSCC

Abstract

CD44, an extracellular matrix (ECM) receptor, has been described as a cancer stem cell marker in multiple cancers, including head and neck squamous cell carcinoma (HNSCC). HNSCC orasphere formation or stemness was characterized by cleavage of CD44, and thus we hypothesized that this proteolytic processing may be critical to stemness and tumorigenesis. We tested this hypothesis by examining the mechanisms that regulate this process in vitro and in vivo, and by exploring its clinical relevance in human specimens. Sphere assays have been used to evaluate stemness in vitro. Spheres comprised of HNSCC cells or oraspheres and an oral cancer mouse model were used to examine the significance of CD44 cleavage using stable suppression and inhibition approaches. These mechanisms were also examined in HNSCC specimens. Oraspheres exhibited increased levels of CD44 cleavage compared to their adherent counterparts. Given that disintegrin and metalloproteinase domain-containing protein 17 (ADAM17) is a major matrix metalloproteinase known to cleave CD44, we chemically inhibited and stably suppressed ADAM17 expression in HNSCC cells and found that these treatments blocked CD44 cleavage and abrogated orasphere formation. Furthermore, stable suppression of ADAM17 in HNSCC cells also diminished tumorigenesis in an oral cancer mouse model. Consistently, stable suppression of CD44 in HNSCC cells abrogated orasphere formation and inhibited tumorigenesis in vivo. The clinical relevance of these findings was confirmed in matched primary and metastatic human HNSCC specimens, which exhibited increased levels of ADAM17 expression and concomitant CD44 cleavage compared to controls. CD44 cleavage by ADAM17 is critical to orasphere formation or stemness and HNSCC tumorigenesis.

Expression and influence of Notch signaling in oral squamous cell carcinoma

“…ADAM17 is a membrane-associated enzyme that cleaves various membrane proteins, including CD44, EGFR, and Notch receptors (43)(44)(45). In human OSCC cell line, overexpression of ADAM17 exhibited higher cell viability, adhesion, and migration in vitro (46).…”

Isolation, Culture and Identification of Choriocarcinoma Stem-Like Cells from the Human Choriocarcinoma Cell-Line JEG-3

“…CD44 is a multifunctional class I transmembrane glycoprotein and specific receptor for hyaluronic acid, promoting migration in normal cells, and is highly expressed in almost every cancer cell in its standard or variant form [29]. It is considered a potential CSC marker in the majority of cancers, including gastric [30], prostate [31], head and neck [32] and lung [33] cancers. ABCG2 is an important member of the ABC transporter superfamily, which has been implicated in multidrug resistance in cancer.…”

Autophagy regulates cisplatin‐induced stemness and chemoresistance via the upregulation of CD44, ABCB1 and ADAM17 in oral squamous cell carcinoma

“…8 ADAM17 (A disintegrin and metalloproteinase) or TACE (TNF-alpha converting enzyme), a membrane protein responsible for the cleavage CD44 ectodomain, extracellular matrix remodelling, invasion and metastasis of cancer, is also associated with inducing stemness and driving tumorigenesis in head and neck cancer. 9 The purpose of this study is to investigate the …”