Abstract B01: pRb activates mitochondrial metabolism and promotes differentiation through the histone demethylase Kdm5a

Abstract

Abstract While largely studied for its role in cell cycle progression, pRb tumor suppressor is also responsible for differentiation. Cells isolated from Rb knockout animals (Rb1-/-), when induced for differentiation, display defects in induction of differentiation markers. Previous studies in our laboratory identified a critical pRB-interacting protein, Kdm5a, which loss rescued the differentiation defect. Kdm5a is a histone demethylase that is specific to the chromatin modification characteristic of active chromatin, histone H3 lysine 4 trimethylation. We found that Kdm5a binds to many genes with function in the mitochondria. Analysis of Rb1-/- mouse embryonic fibroblasts (MEFs) revealed that the mitochondrial genes were down-regulated, but expression of these genes was rescued upon knockout of Kdm5a. Strikingly, overexpression of the factor required for mitochondrial biosynthesis Pgc-1α or the mitofusin protein Mfn2, was sufficient to rescue the differentiation defect in Rb1-/- MEFs. The rescue of differentiation by loss of Kdm5a or by activation of mitochondrial biogenesis revealed the mitochondrial activation as an essential step in restoring differentiation. Here we investigate which specific mitochondrial function is involved in the differentiation rescue, using metabolic flux analysis and gas chromatography tandem mass spectrometry. We present the evidence that Rb1-deficient MEFs have a decreased oxidative capacity compared to the wild type MEFs, while loss of Kdm5a results in a highly increased respiration and TCA cycle metabolites. Overexpression of Pgc-1α and Mfn2 increased oxidative capacity in parallel with the differentiation rescue. In contrast, knockdown of Mfn2 inhibited oxidation as well as differentiation. Similar experiments conducted in Pgc-1α-/- MEFs were consistent with the role for Pgc-1α in increasing oxidative capacity. The data on establishing the link between mitochondrial function and differentiation are important because they may have implications in developing restorative, differentiation-based therapies. Citation Format: Renáta Váraljai, Abul B.M.M.K. Islam, Nicholas J. Dyson, Elizaveta V. Benevolenskaya. pRb activates mitochondrial metabolism and promotes differentiation through the histone demethylase Kdm5a. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Cancer Cell Cycle - Tumor Progression and Therapeutic Response; Feb 28-Mar 2, 2016; Orlando, FL. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(11_Suppl):Abstract nr B01.