Breast cancer-secreted factors induce atrophy and reduce basal and insulin-stimulated glucose uptake by inhibiting Rac1 activation in rat myotubes

Background Metabolic disorders are prevalent in women with breast cancer, increasing mortality and cancer recurrence rates. Despite clinical implications, the cause of breast cancer-associated metabolic dysfunction remains poorly understood. Skeletal muscle is crucial for insulin-stimulated glucose uptake, thus key to whole-body glucose homeostasis. In this study, we determined the effect of breast cancer cell-conditioned media on skeletal muscle glucose uptake in response to insulin. Method L6 myotubes overexpressing myc-tagged GLUT4 (GLUT4myc-L6) were incubated with 40% conditioned media from tumorigenic MCF7 or BT474, or non-tumorigenic control MCF10A breast cells. Mass-spectrometry-based proteomics was applied to detect molecular rewiring in response to breast cancer in the muscle. Expression of myogenesis and inflammation markers, GLUT4 translocation, [ 3 H]-2-deoxyglucose (2DG) uptake, and intramyocellular insulin signalling were determined. Results Breast cancer cell-conditioned media induced proteomic changes in pathways related to sarcomere organisation, actin filament binding, and vesicle trafficking, disrupted myogenic differentiation, activated an inflammatory response via NF-κB, and induced muscle atrophy. Basal and insulin-stimulated GLUT4 translocation and 2DG uptake were reduced in myotubes treated with breast cancer cell-conditioned media compared to the control. Insulin signalling via the Rho GTPase Rac1 was blocked in breast cancer-treated myotubes, while Akt-TBC1D4 signalling was unaffected. Conclusion Conditioned media from MCF7 and BT474 breast cancer cells reduced skeletal muscle glucose uptake via inhibition of GLUT4 translocation and intramyocellular insulin signalling by selectively blocking Rac1 activation and inducing inflammation. These findings indicate that the rewiring of skeletal muscle proteome, inflammation, and insulin signalling could play a role in metabolic dysfunction in patients with breast cancer.