Abstract 6956: Role of soluble CD109 in the progression of head and neck squamous cell carcinoma
Authors: Durgempudi Varsha Reddy , Kungyal Tenzin , Philip Anie 
Published: March 2024

Abstract
Introduction: About five percent of global cancer deaths are attributed to Head and Neck Squamous Cell Carcinoma (HNSCC), and its annual incidence is predicted to skyrocket by thirty percent by 2030 (according to GLOBOCAN estimates). HNSCC originates from squamous cells in the oral cavity, lips, tongue, larynx, pharynx, and salivary glands. Despite the comparatively easy tumor diagnosis, the number of patients diagnosed at an advanced stage with metastatic spread is substantial. Multiple cell-signaling pathways have been proven to be dysregulated in HNSCC, including the epidermal growth factor receptor (EGFR). Our group has identified CD109, a GPI-anchored membrane-associated protein, as a TGF-β co-receptor that inhibits TGF-β signaling. CD109 expression is upregulated in SCC, and its elevated expression in premalignant lesions is associated with an increased risk of metastatic progression. Recent studies by our team have revealed that CD109 promotes tumor growth in vivo, likely by enhancing EGFR signaling. Interestingly, we have also discovered that membrane CD109 (mCD109) is endogenously released from the cell surface; however, the mechanism of action of the released/soluble form of CD109 (sCD109) remains unknown. In the current study, we examined whether sCD109 opposes the mCD109/EGFR-mediated pro-tumorigenic signaling and HNSCC progression.
Research Questions: 1.Does sCD109 regulate EGF-induced EGFR signaling and downstream stem cell marker expression?2.Does sCD109 regulate EGFR expression levels on the HNSCC cell surface?3.Does sCD109 affect the nuclear localization of EGFR?4.Does sCD109 promote EGFR internalization and degradation?
Methodology: HNSCC cells and patient-derived primary cells were treated with/without sCD109 recombinant protein (1nM, 5nM, and 10nM) without and with the EGF induction (10ng/ml for 15 mins) and were analyzed by western blotting, immunofluorescence, and immunocytochemistry. The role of sCD109 in regulating membrane EGFR levels was assessed by flow cytometry and surface protein biotinylation assay.
Results: Our findings demonstrated that sCD109 inhibited EGF-induced phosphorylation of EGFR (Y1068), STAT3, AKT, and ERK. The sCD109 suppressed the stem cell marker expression (Nanog, OCT4, SOX2). Additionally, sCD109 hindered the nuclear localization of activated EGFR. The sCD109 decreased the membrane EGFR expression levels and activated the phosphorylation of EGFR (Y1045), suggesting a role for sCD109 in promoting EGFR degradation.
Conclusion: Our team has previously reported that mCD109 is pro-tumorigenic, and our current findings suggest that sCD109 opposes the pro-tumorigenic effects of mCD109. This study aimed to determine how sCD109 regulates cellular signaling pathways and will provide key insights into the molecular mechanisms underlying the progression of HNSCC, a highly prevalent malignancy.
Citation Format: Varsha Reddy Durgempudi, Tenzin Kungyal, Anie Philip. Role of soluble CD109 in the progression of head and neck squamous cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6956.