Tspan15‐ADAM10 signalling enhances cancer stem cell‐like properties and induces chemoresistance via Notch1 activation in ICC

Abstract Background & Aims Notch1 activation promotes ICC progression and is associated with chemoresistance; however, therapies directly targeting Notch1 showed severe adverse effects. Notch1 activation is mediated by ADAM10, a molecular scissor that separates the target protein from its substrates in the cell membrane. Tspan15 regulates ADAM10 function, but the role of Tspan15 in ICC progression is unclear. Methods Tspan15, ADAM10, and Notch1 expression and activation in fresh surgical specimens from 80 ICC patients and ICC cells were evaluated by immunohistochemistry, RT‐PCR, western blotting, and flow cytometry. Results Tspan15 expression was increased in ICC compared with adjacent liver tissue, and high Tspan15 expression was an independent factor for poor prognosis. In ICC with high Tspan15 expression, vascular invasion, lymph node metastasis, and haematogenous recurrence were increased. Tspan15 was co‐expressed with ADAM10 in ICC, and associated with the expression of stemness and EMT markers. In ICC cells, Tspan15 induced ADAM10 activation by mediating the translocation of activated m‐ADAM10 from the cytoplasm to the surface of the cell membrane, which further activated Notch1 by separating the intracellular domain of Notch1 from its extracellular domain, leading to enhancement of CSC‐like properties and EMT. This signalling was associated with enhanced chemoresistance against gemcitabine and cisplatin. Inhibition of Tspan15 or ADAM10 is a promising therapeutic strategy in ICC, as Tspan15 or ADAM10 knockdown or treatment with ADAM10 inhibitor reduced chemoresistance and invasiveness by suppressing Notch1‐mediated CSC‐like properties and EMT. Conclusions Tspan15‐ADAM10‐Notch1 signalling is associated with aggressive tumour progression and poor prognosis in ICC.