IL-6-mediated tumorigenicity and antioxidant state in squamous cell carcinoma cells are driven by CD109 via stabilization of IL-6 receptor-alpha and activation of STAT3/NRF2 pathway.

Background: Squamous cell carcinoma (SCC) is a prevalent malignancy and there are limited options to block the recurrence and metastasis that often occur in SCC patients. Although IL-6, a proinflammatory cytokine, is strongly implicated in SCC pathogenesis, its mechanism of action is poorly understood. The GPI-anchored membrane protein CD109 is frequently overexpressed in SCC and is associated with malignant transformation. The current study aims to investigate whether CD109 interacts with IL-6 receptor alpha (IL6Rα) and promotes IL-6-mediated oncogenic signaling to drive SCC progression.

Methods: IL6Rα interaction with CD109 was determined by coimmunoprecipitation, immunohistochemistry, immunofluorescence and FACS analysis using human SCC (oral and vulvar) cell lines and human oral SCC tumors versus control tissue. Regulation of IL-6-induced signaling and antioxidant responses by CD109 was analyzed via STAT3/NRF2/SOD1/HO1 pathway activation. Regulation of IL-6-mediated tumorigenicity by CD109 was determined using stem cell marker expression and a spheroid formation assay. Clinical validation was achieved using genomic and proteomic analysis of oral SCC tumors and of head and neck SCC patient data.

Results: We show that CD109 interacts with and stabilizes IL6Rα expression and promotes IL-6/STAT3/NRF2 pathway in oral and vulvar SCC cells. Loss of CD109 attenuates this pathway leading to loss of cancer cell stemness and decreased expression of superoxide dismutase1 and heme oxygenase-1, antioxidant proteins important for cell survival after chemotherapy. Furthermore, clinical validation of these findings was achieved through multi-omic analysis of oral SCC tumors and of head and neck SCC patient data.

Conclusions: This work uncovers a previously unidentified mechanism in which CD109 serves as an essential regulator of IL6Rα expression and IL-6 mediated signaling in SCC cells, promoting stemness and antioxidant state, mechanisms known to mediate therapy resistance in SCC. Our findings establish a mechanistic validation for investigating the therapeutic utility of the CD109/ IL6Rα/STAT3/NRF2 pathway in SCC.