FOXK2 targeting by the SCF-E3 ligase subunit FBXO24 for ubiquitin mediated degradation modulates mitochondrial respiration
FOXK2 is a crucial transcription factor implicated in a wide array of biological activities and yet understanding of its molecular regulation at the level of protein turnover is limited. Here we identify that FOXK2 is sensitive to degradation by the virulent pathogens P. aeruginosa and K. pneumoniae in lung epithelia through ubiquitin-proteasomal processing. FOXK2 through its carboxyl-terminus (aa 428-478) binds the Skp-Cullin-F-box ubiquitin E3 ligase subunit FBXO24 that mediates multisite polyubiquitylation of the transcription factor resulting in its nuclear degradation. FOXK2 was detected within mitochondria and targeted depletion of the transcription factor or cellular expression of FOXK2 mutants devoid of key carboxyl-terminal domains significantly impaired mitochondrial function. In experimental bacterial pneumonia, Fbxo24 heterozygous mice exhibited preserved mitochondrial function and Foxk2 protein levels compared to wild-type littermates. The results suggest a new mode of regulatory control of mitochondrial energetics through modulation of FOXK2 cellular abundance. Overall design: To investigate the biological function of FOXK2 in lung epithelial cells (Beas-2B), we knowdown FoxK2 using siRNA. We then performed gene expression profile analysis using data obtained from RNA-seq of 2 different siRNA specific for FoxK2  and a control cells with scrambled RNA