Differential AXL expression and regulation of Arf1 controls matrix stiffness-dependent Golgi organization and function in breast cancer cells
Integrin-mediated cell-matrix adhesion regulates cell growth and survival and is often deregulated in transformed cancer cells, promoting anchorage independence. Integrins are essential regulators of cellular mechanotransduction, known to be altered in cancer cells. In breast cancers, tumour stiffening is a well-characterized feature of the disease progression. The Golgi apparatus, regulated by integrin-mediated adhesion in responding to mechanosensory cues, could support cancer progression. MDAMB231 and MCF7 cells with distinct Golgi organization and altered mechanosensing were evaluated. In MDAMB231 cells the organized Golgi in stable adherent cells becomes disorganised on loss of adhesion. This contrasts with MCF7 cells, where the Golgi remains disorganized regardless of the adhesion status. In MDAMB231 cells, increasing matrix stiffness promotes Golgi organization and regulates Golgi-dependent microtubule acetylation. In MCF7 cells, the Golgi stays disorganised despite increasing stiffness. Both cell types show stiffness-dependent cell spreading, with MCF7 cells spreading more efficiently than MDAMB231 cells - a difference that may be partially mediated by their differential Golgi organization. AXL, a receptor tyrosine kinase, is known to be involved in rigidity sensing and is differentially expressed in MDAMB231 (high) vs MCF7 (no expression) cells. AXL inhibition (by R428) and siRNA-mediated AXL knockdown disrupt stiffness-dependent Golgi organization in MDAMB231 cells, promoting cell spreading. Transient and stable AXL expression in MCF7 cells causes the Golgi to become predominantly organised and respond to higher matrix stiffness, affecting cell spreading. Stiffness-dependent AXL expression supports stiffness-dependent Arf1 expression and activation to drive Golgi organization. Thus, matrix mechanosensing through the AXL-Arf1-Golgi pathway could regulate vital cellular processes in breast cancer cells.