Tetraspanin CD9 interacts with α-secretase to enhance its oncogenic function in pancreatic cancer

Pancreatic cancer is one of the most lethal cancers and its prognosis remains poor. ADAM family proteins like ADAM10, ADAM9 and ADAM17 function as alpha-secretase to cleavage cell surface proteins like Notch to facilitate oncogenesis in various tumors. The oncogenic roles of alpha-secretase in PDAC have been demonstrated but it remains unknown that whether and how alpha-secretase is regulated in PDAC. Here, we report that the expression of tetraspanin CD9 was increased and strongly associated with poor prognosis in PDAC. CD9 expression was positively associated with alpha-secretase activity in PDAC tissues and CD9 knock-down inhibited alpha-secretase activity in PDAC cell lines. Co-immunoprecipitation and GST pull down demonstrates that CD9 directly interacted with ADAM10, ADAM9 and ADAM17, respectively. Cell surface biotin labeling and immunostaining of tagged ADAM proteins show that CD9 promoted cell surface trafficking of ADAM family proteins. In addition, the antibody targeting extracellular domain of CD9 disrupted the interactions between CD9 and ADAM family proteins, reduced cell surface trafficking of ADAM proteins and inhibited alpha-secretase activity. Notch signaling was inhibited by CD9 knockdown or CD9 antibody in cell lines. Finally, CD9 antibody showed anti-tumor effects in cell proliferation MTT assay, transwell migration assay and colony formation assay. Our study reveals a novel CD9/ADAM/Notch signaling network in PDAC and it supports that targeting CD9 ADAM interaction with antibody may be a potential therapeutic intervention for PDAC.