SUMMARY Catecholamines promote lipolysis both in brown and white adipocytes, whereas the same stimuli preferentially activate thermogenesis in brown adipocytes. Molecular mechanisms for the adipose-selective activation of thermogenesis remain poorly understood. Here, we employed quantitative phosphoproteomics to map global and temporal phosphorylation profiles in brown, beige, and white adipocytes under β3-adrenenoceptor activation and identified kinases responsible for the adipose-selective phosphorylation profiles. We found that casein kinase2 (CK2) activity is preferentially higher in white adipocytes than brown/beige adipocytes. Genetic or pharmacological blockade of CK2 in white adipocytes activates the thermogenic program in response to cAMP stimuli. Such activation is largely through reduced CK2-mediated phosphorylation of class I HDACs. Notably, inhibition of CK2 promotes beige adipocyte biogenesis and leads to an increase in whole-body energy expenditure and ameliorates diet-induced obesity and insulin resistance. These results indicate that CK2 is a plausible target to rewire the β3-adreneno-ceptor signaling cascade that promotes thermogenesis in adipocytes.

SignificanceThe most abundant modification in mRNA is the N6-methylation of internal adenosines (m6A), but m6A’s physiological function is unknown for most mRNAs. Here we show that Casein Kinase 1 Delta mRNA (Ck1δ), coding for a critical kinase in the control of circadian rhythms, is regulated by m6A. When m6A is inhibited, the expression of two CK1δ isoforms, uncharacterized until now, increases due to enhanced translation. This increase in CK1δs leads to a slower clock because of increased phosphorylation of the clock protein PER2 at a key residue, leading to the stabilization of PER2 protein.

Ectopic expression of the mitochondrial F 1 F 0 -ATP synthase on the plasma membrane has been reported to occur in cancer, but whether it exerts a functional role in this setting remains unclear. Here we show that ectopic ATP synthase and the electron transfer chain exist on the plasma membrane in a punctuated distribution of lung adenocarcinoma cells, where it is critical to support cancer cell proliferation. Applying ATP synthase inhibitor citreoviridin induced cell cycle arrest and inhibited proliferation and anchorage-independent growth of lung cancer cells. Analysis of protein expression profiles after citreoviridin treatment suggested this compound induced the unfolded protein response (UPR) associated with phosphorylation the translation initiation factor 2a (eIF2a), triggering cell growth inhibition. Citreoviridin-enhanced eIF2a phosphorylation could be reversed by siRNA-mediated attenuation of the UPR kinase PKR-like endoplasmic reticulum kinase (PERK) combined with treatment with the antioxidant N-acetylcysteine, establishing that reactive oxygen species (ROS) boost UPR after citreoviridin treatment. Thus, a coordinate elevation of UPR and ROS initiates a positive feedback loop that convergently blocks cell proliferation. Our findings define a molecular function for ectopic ATP synthase at the plasma membrane in lung cancer cells and they prompt further study of its inhibition as a potential therapeutic approach. Cancer Res; 72(18); 4696-706. Ó2012 AACR.