Butyrylation Meets Adipogenesis-Probed by a p300-Catalyzed Acylation-Specific Small Molecule Inhibitor: Implication in Anti-obesity Therapy.

The enzyme p300, besides having acetyltransferase activity, can also catalyze other acylation modifications, whose physiological implications are still being investigated. Here, we report that the level of histone butyrylation increases globally as well as locally in the promoters of pro-adipogenic genes during adipogenesis. To delineate the role of p300-catalyzed butyrylation from acetylation in adipogenesis, we identified a semisynthetic derivative (LTK-14A) of garcinol, which specifically inhibited histone butyrylation without affecting acetylation. Treatment of 3T3L1 cells with LTK-14A abolished adipogenesis with downregulation of pro-adipogenic genes along with inhibition of H4K5 butyrylation. Administering LTK-14A to high-fat diet-fed and genetically obese db/db mice led to attenuation/decrease in their weight gain. The reduced obesity could be partially attributed to the inhibition of H4K5 butyrylation in adipocytes and liver. This report therefore not only, for the first time, causally links histone butyrylation with adipogenesis but also presents a probable candidate for anti-obesity therapeutics.

Garcinol and Its Role in Chronic Diseases.

The various bioactive compounds isolated from leaves and fruits of Garcinia sps plants, have been characterized and experimentally demonstrated to be anti-oxidant, anti-inflammatory and anti-cancer in nature. Garcinol, a polyisoprenylated benzophenone, obtained from plant Garcinia indica has been found to be an effective inhibitor of several key regulatory pathways (e.g., NF-kB, STAT3 etc.) in cancer cells, thereby being able to control malignant growth of solid tumours in vivo. Despite its high potential as an anti-neoplastic modulator of several cancer types such as head and neck cancer, breast cancer, hepatocellular carcinoma, prostate cancer, colon cancer etc., it is still in preclinical stage due to lack of systematic and conclusive evaluation of pharmacological parameters. While it is promising anti-cancer effects are being positively ascertained for therapeutic development, studies on its effectiveness in ameliorating other chronic diseases such as cardiovascular diseases, diabetes, allergy, neurodegenerative diseases etc., though seem favourable, are very recent and require in depth scientific investigation.

Inhibition of STAT3 dimerization and acetylation by garcinol suppresses the growth of human hepatocellular carcinoma in vitro and in vivo.

BACKGROUND: Constitutive activation of signal transducer and activator of transcription 3 (STAT3) has been linked with proliferation, survival, invasion and angiogenesis of a variety of human cancer cells, including hepatocellular carcinoma (HCC). Thus, novel agents that can suppress STAT3 activation have potential for both prevention and treatment of HCC. Here we report, garcinol, a polyisoprenylated benzophenone, could suppress STAT3 activation in HCC cell lines and in xenografted tumor of HCC in nude mice model. EXPERIMENTAL DESIGN: Different HCC cell lines have been treated with garcinol and the inhibition of STAT3 activation, dimerization and acetylation have been checked by immunoblotting, immuno-fluorescence, and DNA binding assays. Xenografted tumor model has been generated in nude mice using HCC cell line and effect of garcinol in the inhibition of tumor growth has been investigated. RESULTS: Garcinol could inhibit both constitutive and interleukin (IL-6) inducible STAT3 activation in HCC cells. Computational modeling showed that garcinol could bind to the SH2 domain of STAT3 and suppress its dimerization in vitro. Being an acetyltransferase inhibitor, garcinol also inhibits STAT3 acetylation and thus impairs its DNA binding ability. The inhibition of STAT3 activation by garcinol led to the suppression of expression of various genes involved in proliferation, survival, and angiogenesis. It also suppressed proliferation and induced substantial apoptosis in HCC cells. Remarkably, garcinol inhibited the growth of human HCC xenograft tumors in athymic nu/nu mice, through the inhibition of STAT3 activation. CONCLUSION: Overall, our results suggest that garcinol exerts its anti-proliferative and pro-apoptotic effects through suppression of STAT3 signaling in HCC both in vitro and in vivo.

Probing p300/CBP associated factor (PCAF)-dependent pathways with a small molecule inhibitor.

PCAF (KAT2B) belongs to the GNAT family of lysine acetyltransferases (KAT) and specifically acetylates the histone H3K9 residue and several nonhistone proteins. PCAF is also a transcriptional coactivator. Due to the lack of a PCAF KAT-specific small molecule inhibitor, the exclusive role of the acetyltransferase activity of PCAF is not well understood. Here, we report that a natural compound of the hydroxybenzoquinone class, embelin, specifically inhibits H3Lys9 acetylation in mice and inhibits recombinant PCAF-mediated acetylation with near complete specificity in vitro. Furthermore, using embelin, we have identified the gene networks that are regulated by PCAF during muscle differentiation, further highlighting the broader regulatory functions of PCAF in muscle differentiation in addition to the regulation via MyoD acetylation.

Specific inhibition of p300-HAT alters global gene expression and represses HIV replication.

Reversible acetylation of histone and nonhistone proteins plays pivotal role in cellular homeostasis. Dysfunction of histone acetyltransferases (HATs) leads to several diseases including cancer, neurodegenaration, asthma, diabetes, AIDS, and cardiac hypertrophy. We describe the synthesis and characterization of a set of p300-HAT-specific small-molecule inhibitors from a natural nonspecific HAT inhibitor, garcinol, which is highly toxic to cells. We show that the specific inhibitor selectively represses the p300-mediated acetylation of p53 in vivo. Furthermore, inhibition of p300-HAT down regulates several genes but significantly a few important genes are also upregulated. Remarkably, these inhibitors were found to be nontoxic to T cells, inhibit histone acetylation of HIV infected cells, and consequently inhibit the multiplication of HIV.