ROS disrupt COP9 signalosome-mediated ABCA1 protection and trigger its ubiquitination and degradation by cullin3 inhibiting cholesterol efflux and promoting foam cell formation in response to GPCR agonists

In this study, we investigated the intricate mechanisms underlying thrombin and Ang II-induced depletion of ABCA1. Under basal conditions, the COP9 signalosome interacts with ABCA1 as a whole complex rather than as individual subunits. In the presence of GPCR-agonists, thrombin or angiotensin II (Ang II), ABCA1 was phosphorylated and dissociated from COP9 signalosome, paving the way for its cullin3-mediated ubiquitination and degradation. Furthermore, forced expression of CSN5, the catalytic core subunit of the COP9 signalosome, inhibited thrombin or Ang II-induced ubiquitination and degradation of ABCA1, thereby restoring cholesterol efflux and suppressing foam cell formation. In addition, xanthine oxidase-dependent H₂O₂ production was required for both thrombin and Ang II-induced downregulation of ABCA1 levels and inhibition of cholesterol efflux promoting foam cell formation. Additionally, we identified the involvement of Gα12-Pyk2-Gab1-PKCθ signaling downstream to thrombin and Ang II receptors, namely, Par1 and AT1R in the modulation of these effects. Corroborating these observations, we found that while CSN5 and ABCA1 were found to be colocalized in human non-stenotic coronary artery sections and the aortic root cross sections of CD-fed ApoE^-/- mice, ABCA1 levels were diminished in advanced human atherosclerotic lesions and in the aortic root cross sections of WD-fed ApoE^-/- mice. Collectively, these findings reveal a novel role for xanthine oxidase-dependent H₂O₂ production in the GPCR agonists-induced destabilization of ABCA1 resulting in reduced cholesterol efflux and increased foam cell formation.