Tumour suppressor Fus1 provides a molecular link between inflammatory response and mitochondrial homeostasis

Fus1, encoded by a 3p21.3 tumour suppressor gene, is down-regulated, mutated or lost in the majority of inflammatory thoracic malignancies. The mitochondrial localization of Fus1 stimulated us to investigate how Fus1 modulates inflammatory response and mitochondrial function in a mouse model of asbestos-induced peritoneal inflammation. Asbestos treatment resulted in a decreased Fus1 expression in wild-type (WT) peritoneal immune cells, suggesting that asbestos exposure may compromise the Fus1-mediated inflammatory response. Untreated Fus1−/− mice had an ∼eight-fold higher proportion of peritoneal granulocytes than Fus1+/+ mice, pointing at ongoing chronic inflammation. Fus1−/− mice exhibited a perturbed inflammatory response to asbestos, reflected in decreased immune organ weight and peritoneal fluid protein concentration, along with an increased proportion of peritoneal macrophages. Fus1−/− immune cells showed augmented asbestos-induced activation of key inflammatory, anti-oxidant and genotoxic stress response proteins ERK1/2, NFκB, SOD2, γH2AX, etc. Moreover, Fus1−/− mice demonstrated altered dynamics of pro- and anti-inflammatory cytokine expression, such as IFNγ, TNFα, IL-1A, IL-1B and IL-10. ‘Late’ response cytokine Ccl5 was persistently under-expressed in Fus1−/− immune cells at both basal and asbestos-activated states. We observed an asbestos-related difference in the size of CD3+ CD4− CD8− DN T cell subset that was expanded four-fold in Fus1−/− mice. Finally, we demonstrated Fus1-dependent basal and asbestos-induced changes in major mitochondrial parameters (ROS production, mitochondrial potential and UCP2 expression) in Fus1−/− immune cells and in Fus1-depleted cancer cells, thus supporting our hypothesis that Fus1 establishes its immune- and tumour-suppressive activities via regulation of mitochondrial homeostasis. Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.