Acetylation modulates prolactin receptor dimerization

HDAC5 controls a hypothalamic STAT5b-TH axis, the sympathetic activation of ATP-consuming futile cycles and adult-onset obesity in male mice

With age, metabolic perturbations accumulate to elevate our obesity burden. While age-onset obesity is mostly driven by a sedentary lifestyle and high calorie intake, genetic and epigenetic factors also play a role. Among these, members of the large histone deacetylase (HDAC) family are of particular importance as key metabolic determinants for healthy ageing, or metabolic dysfunction. Here, we aimed to interrogate the role of class 2 family member HDAC5 in controlling systemic metabolism and age-related obesity under non-obesogenic conditions. Starting at 6 months of age, we observed adult-onset obesity in chow-fed male global HDAC5-KO mice, that was accompanied by marked reductions in adrenergic-stimulated ATP-consuming futile cycles, including BAT activity and UCP1 levels, WAT-lipolysis, skeletal muscle, WAT and liver futile creatine and calcium cycles, and ultimately energy expenditure. Female mice did not differ between genotypes. The lower peripheral sympathetic nervous system (SNS) activity in mature male KO mice was linked to higher dopaminergic neuronal activity within the dorsomedial arcuate nucleus (dmARC) and elevated hypothalamic dopamine levels. Mechanistically, we reveal that hypothalamic HDAC5 acts as co-repressor of STAT5b over the control of Tyrosine hydroxylase (TH) gene transactivation, which ultimately orchestrates the activity of dmARH dopaminergic neurons and energy metabolism in male mice under non-obesogenic conditions.

Mechanisms and functions of SUMOylation in health and disease: a review focusing on immune cells

SUMOylation, which is a type of post-translational modification that involves covalent conjugation of small ubiquitin-like modifier (SUMO) proteins to target substrates, regulates various important molecular and cellular processes, including transcription, the cell cycle, cell signaling, and DNA synthesis and repair. Newly synthesized SUMO is immature and cleaved by the SUMO-specific protease family, resulting in exposure of the C-terminal Gly-Gly motif to become the mature form. In the presence of ATP, mature SUMO is conjugated with the activating enzyme E1 through the cysteine residue of E1, followed by transfer to the cysteine residue of E2-conjugating enzyme Ubc9 in humans that recognizes and modifies the lysine residue of a substrate protein. E3 SUMO ligases promote SUMOylation. SUMOylation is a reversible modification and mediated by SUMO-specific proteases. Cumulative studies have indicated that SUMOylation affects the functions of protein substrates in various manners, including cellular localization and protein stability. Gene knockout studies in mice have revealed that several SUMO cycling machinery proteins are crucial for the development and differentiation of various cell lineages, including immune cells. Aberrant SUMOylation has been implicated in several types of diseases, including cancers, cardiovascular diseases, and autoimmune diseases. This review summarizes the biochemistry of SUMO modification and the general biological functions of proteins involved in SUMOylation. In particular, this review focuses on the molecular mechanisms by which SUMOylation regulates the development, maturation, and functions of immune cells, including T, B, dendritic, and myeloid cells. This review also discusses the underlying relevance of disruption of SUMO cycling and site-specific interruption of SUMOylation on target proteins in immune cells in diseases, including cancers and infectious diseases.

Adipose Tissue Macrophage-Mediated Inflammation in Obesity: A Link to Posttranslational Modification

Adipose tissue macrophages (ATM) are an essential type of immune cells in adipose tissue. Obesity induces the inflammation of adipose tissues, as expressed by ATM accumulation, that is more likely to become a source of systemic metabolic diseases, including insulin resistance. The process is characterized by the transcriptional regulation of inflammatory pathways by virtue of signaling molecules such as cytokines and free fatty acids. Notably, posttranslational modification (PTM) is a key link for these signaling molecules to trigger the proinflammatory or anti-inflammatory phenotype of ATMs. This review focuses on summarizing the functions and molecular mechanisms of ATMs regulating inflammation in obese adipose tissue. Furthermore, the role of PTM is elaborated, hoping to identify new horizons of treatment and prevention for obesity-mediated metabolic disease.

A regulatory circuit comprising the CBP and SIRT7 regulates FAM134B-mediated ER-phagy

Macroautophagy (autophagy) utilizes a serial of receptors to specifically recognize and degrade autophagy cargoes, including damaged organelles, to maintain cellular homeostasis. Upstream signals spatiotemporally regulate the biological functions of selective autophagy receptors through protein post-translational modifications (PTM) such as phosphorylation. However, it is unclear how acetylation directly controls autophagy receptors in selective autophagy. Here, we report that an ER-phagy receptor FAM134B is acetylated by CBP acetyltransferase, eliciting intense ER-phagy. Furthermore, FAM134B acetylation promoted CAMKII-mediated phosphorylation to sustain a mode of milder ER-phagy. Conversely, SIRT7 deacetylated FAM134B to temper its activities in ER-phagy to avoid excessive ER degradation. Together, this work provides further mechanistic insights into how ER-phagy receptor perceives environmental signals for fine-tuning of ER homeostasis and demonstrates how nucleus-derived factors are programmed to control ER stress by modulating ER-phagy.

Sirt6 attenuates chondrocyte senescence and osteoarthritis progression

Sirt6 has been implicated as a key regulator in aging-related diseases, including osteoarthritis. However, its functional role and molecular mechanism in chondrocyte senescence and osteoarthritis pathophysiology remain largely undefined. Here we show that Sirt6 deficiency exaggerates chondrocyte senescence and osteoarthritis progression, whereas intra-articular injection of adenovirus-Sirt6 markedly attenuates surgical destabilization of medial meniscus-induced osteoarthritis. Mechanistically, Sirt6 can directly interact with STAT5 and deacetylate STAT5, thus inhibiting the IL-15/JAK3-induced STAT5 translocation from cytoplasm to nucleus, which inactivates IL-15/JAK3/STAT5 signaling. Mass spectrometry revealed that Sirt6 deacetylated conserved lysine 163 on STAT5. Mutation of lysine 163 to arginine in STAT5 abolished the regulatory effect of Sirt6. In vivo, specific ablation of Sirt6 in chondrocytes exacerbated osteoarthritis. Pharmacological activation of Sirt6 substantially alleviated chondrocyte senescence. Taken together, Sirt6 attenuates chondrocyte senescence by inhibiting IL-15/JAK3/STAT5 signaling. Targeting Sirt6 represents a promising new approach for osteoarthritis.

Advances in Immunosuppressive Agents Based on Signal Pathway

Immune abnormality involves in various diseases, such as infection, allergic diseases, autoimmune diseases, as well as transplantation. Several signal pathways have been demonstrated to play a central role in the immune response, including JAK/STAT, NF-κB, PI3K/AKT-mTOR, MAPK, and Keap1/Nrf2/ARE pathway, in which multiple targets have been used to develop immunosuppressive agents. In recent years, varieties of immunosuppressive agents have been approved for clinical use, such as the JAK inhibitor tofacitinib and the mTOR inhibitor everolimus, which have shown good therapeutic effects. Additionally, many immunosuppressive agents are still in clinical trials or preclinical studies. In this review, we classified the immunosuppressive agents according to the immunopharmacological mechanisms, and summarized the phase of immunosuppressive agents.

A novel resveratrol analog upregulates sirtuin 1 and inhibits inflammatory cell infiltration in acute pancreatitis

Acute pancreatitis (AP), an inflammatory disorder of the pancreas, is a complicated disease without specific drug therapy. (R)-4,6-dimethoxy-3-(4-methoxy phenyl)-2,3-dihydro-1H-indanone [(R)-TML104] is a synthesized analog of the natural product resveratrol sesquiterpenes (±) -isopaucifloral F. This study aimed to investigate the effect and underlying mechanism of (R)-TML104 on AP. The experimental AP model was induced by caerulein hyperstimulation in BALB/c mice. (R)-TML104 markedly attenuated caerulein-induced AP, as evidenced by decreased pancreatic edema, serum amylase levels, serum lipase levels, and pancreatic myeloperoxidase activity. In addition, (R)-TML104 significantly inhibited the expression of pancreatic chemokines C-C motif chemokine ligand 2 and macrophage inflammatory protein-2 and the infiltration of neutrophils and macrophages. Mechanistically, (R)-TML104 activated AMP-activated protein kinase and induced sirtuin 1 (SIRT1) expression. (R)-TML104 treatment markedly induced the SIRT1-signal transducer and activator of transcription 3 (STAT3) interaction and reduced acetylation of STAT3, thus inhibiting the inflammatory response mediated by the interleukin 6-STAT3 pathway. The effect of (R)-TML104 on SIRT1-STAT3 interaction was reversed by treatment with a SIRT1 inhibitor selisistat (EX527). Together, our findings indicate that (R)-TML104 alleviates experimental pancreatitis by reducing the infiltration of inflammatory cells through modulating SIRT1.

Emerging roles of Sirtuin 2 in cardiovascular diseases

Sirtuins are a family of NAD⁺ -dependent deacetylases implicated in a wide variety of age-associated pathologies, including cardiovascular disorders. Among the seven mammalian sirtuins, SIRT2 modulates various cellular processes through the deacetylation or deacylation of their target proteins. Notably, the levels of SIRT2 in the heart decline with age and other pathological conditions, leading to cardiovascular dysfunction. In the present review, we discuss the emerging roles of SIRT2 in cardiovascular dysfunction and heart failure associated with factors like age, hypertension, oxidative stress, and diabetes. We also discuss the potential of using inhibitors to study the unexplored role of SIRT2 in the heart. While SIRT2 undoubtedly plays a crucial role in the cardiovascular system, its functions are only beginning to be understood, making it an attractive candidate for further research in the field.

Acetylation-dependent glutamate receptor GluR signalosome formation for STAT3 activation in both transcriptional and metabolism regulation

Besides their original regulating roles in the brain, spinal cord, retina, and peripheral nervous system for mediating fast excitatory synaptic transmission, glutamate receptors consisting of metabotropic glutamate receptors (GluRs) and ionotropic glutamate receptors (iGluRs) have emerged to have a critical role in the biology of cancer initiation, progression, and metastasis. However, the precise mechanism underpinning the signal transduction mediated by ligand-bound GluRs is not clearly elucidated. Here, we show that iGluRs, GluR1 and GluR2, are acetylated by acetyltransferase CREB-binding protein upon glutamate stimulation of cells, and are targeted by lysyl oxidase-like 2 for deacetylation. Acetylated GluR1/2 recruit β-arrestin1/2 and signal transducer and activator of transcription 3 (STAT3) to form a protein complex. Both β-arrestin1/2 and STAT3 are subsequently acetylated and activated. Simultaneously, activated STAT3 acetylated at lysine 685 translocates to mitochondria to upregulate energy metabolism-related gene transcription. Our results reveal that acetylation-dependent formation of GluR1/2-β-arrestin1/2-STAT3 signalosome is critical for glutamate-induced cell proliferation.

Effects of prolactin on ventricular myocyte shortening and calcium transport in the streptozotocin-induced diabetic rat

The physiological role of prolactin (PRL) in the heart, and in particular the diabetic heart, are largely unknown. The effects of PRL on ventricular myocyte shortening and Ca²⁺ transport in the streptozotocin (STZ) – induced diabetic and in age-matched control rats were investigated. PRL receptor protein, myocyte shortening, intracellular [Ca²⁺], L-type Ca²⁺ current were measured by Western blot, cell imaging, fluorescence photometry and whole-cell patch-clamp techniques, respectively. Compared to normal Tyrode solution (NT), PRL (50 ng/ml) significantly (p < 0.05) increased the amplitude of shortening in myocytes from control (7.43 ± 0.38 vs. 9.68 ± 0.46 %) and diabetic (6.57 ± 0.24 vs. 8.91 ± 0.44 %) heart (n = 44–49 cells). Compared to NT, PRL (50 ng/ml) significantly increased the amplitude of Ca²⁺ transients in myocytes from control (0.084 ± 0.004 vs. 0.115 ± 0.007 Fura-2 ratio units) and diabetic (0.087 ± 0.007 vs. 0.112 ± 0.006 Fura-2 ratio units) heart (n = 36–50 cells). PRL did not significantly alter the amplitude of caffeine-evoked Ca²⁺ transients however, PRL significantly increased the fractional release of Ca²⁺ in myocytes from control (21 %) and diabetic (14 %) and heart. The rate of Ca²⁺ transient recovery following PRL treatment was significantly increased in myocytes from diabetic and control heart. Amplitude of L-type Ca²⁺ current was not significantly altered by diabetes or by PRL. PRL increased the amplitude of shortening and Ca²⁺ transients in myocytes from control and diabetic heart. Increased fractional release of sarcoplasmic reticulum Ca²⁺ may partly underlie the positive inotropic effects of PRL in ventricular myocytes from control and STZ-induced diabetic rat.

Acetylation of STX17 (syntaxin 17) controls autophagosome maturation

The fusion of autophagosomes and endosomes/lysosomes, also called autophagosome maturation, ensures the degradation of autophagic cargoes. It is an important regulatory step of the macroautophagy/autophagy process. STX17 is the key autophagosomal SNARE protein that mediates autophagosome maturation. Here, we report that the acetylation of STX17 regulates its SNARE activity and autophagic degradation. The histone acetyltransferase CREBBP/CBP and the deacetylase HDAC2 specifically regulate the acetylation of STX17. In response to cell starvation and MTORC1 inhibition, the inactivation of CREBBP leads to the deacetylation of STX17 at its SNARE domain. This deacetylation promotes the interaction between STX17 and SNAP29 and the formation of the STX17-SNAP29-VAMP8 SNARE complex with no effect on the recruitment of STX17 to autophagosomal membranes. Deacetylation of STX17 also enhances the interaction between STX17 and the tethering complex HOPS, thereby further promoting autophagosome-lysosome fusion. Our study suggests a mechanism by which acetylation regulates the late-stage of autophagy, and possibly other STX17-related intracellular membrane fusion events.Abbreviations: ACTB: actin beta; CREBBP/CBP: CREB binding protein; Ctrl: control; GFP: green fluorescent protein; GST: glutathione S-transferase; HDAC: histone deacetylase; HOPS: homotypic fusion and protein sorting complex; KO: knockout; LAMP1/2: lysosomal associated membrane protein 1/2; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MEFs: mouse embryonic fibroblasts; MS: mass spectrometry; MTORC1: mechanistic target of rapamycin kinase complex 1; NAM: nicotinamide; PtdIns3K: phosphatidylinositol 3-kinase; RFP: red fluorescent protein; SNAP29: synaptosome associated protein 29; SNARE: soluble N-ethylamide-sensitive factor attachment protein receptor; SQSTM1/p62: sequestosome 1; STX17: syntaxin 17; TSA: trichostatin A; TSC1/2: TSC complex subunit 1/2; VAMP8: vesicle associated membrane protein 8; WT: wild type.

Prolactin, Estradiol and Testosterone Differentially Impact Human Hippocampal Neurogenesis in an In Vitro Model

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Human hippocampal progenitor cells (HPCs) and tissue express classical sex hormone receptors.

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Prolactin does not impact human HPCs maintained in a proliferative state.

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Prolactin increases neuronal differentiation of human HPCs only in the short term.

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Estradiol and testosterone both increase the cell density of proliferating HPCs.

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Estradiol and testosterone have no observed effect on differentiating HPCs.

Previous studies have indicated that sex hormones such as prolactin, estradiol and testosterone may play a role in the modulation of adult hippocampal neurogenesis (AHN) in rodents and non-human primates, but so far there has been no investigation of their impact on human hippocampal neurogenesis. Here, we quantify the expression levels of the relevant receptors in human post-mortem hippocampal tissue and a human hippocampal progenitor cell (HPC) line. Secondly, we investigate how these hormones modulate hippocampal neurogenesis using a human in vitro cellular model. Human female HPCs were cultured with biologically relevant concentrations of either prolactin, estradiol or testosterone. Bromodeoxyuridine (BrdU) incorporation, immunocytochemistry (ICC) and high-throughput analyses were used to quantify markers determining cell fate after HPCs were either maintained in a proliferative state or allowed to differentiate in the presence of these hormones. In proliferating cells, estrogen and testosterone increased cell density but had no clear effect on markers of proliferation or cell death to account for this. In differentiating cells, a 3-day treatment of prolactin elicited a transient effect, whereby it increased the proportion of microtubule-associated protein 2 (MAP2)-positive and Doublecortin (DCX)-positive cells, but this effect was not apparent after 7-days. At this timepoint we instead observe a decrease in proliferation. Overall, our study demonstrates relatively minor, and possibly short-term effects of sex hormones on hippocampal neurogenesis in human cells. Further work will be needed to understand if our results differ to previous animal research due to species-specific differences, or whether it relates to limitations of our in vitro model.

Modulation of M2 macrophage polarization by the crosstalk between Stat6 and Trim24

Stat6 is known to drive macrophage M2 polarization. However, how macrophage polarization is fine-tuned by Stat6 is poorly understood. Here, we find that Lys383 of Stat6 is acetylated by the acetyltransferase CREB-binding protein (CBP) during macrophage activation to suppress macrophage M2 polarization. Mechanistically, Trim24, a CBP-associated E3 ligase, promotes Stat6 acetylation by catalyzing CBP ubiquitination at Lys119 to facilitate the recruitment of CBP to Stat6. Loss of Trim24 inhibits Stat6 acetylation and thus promotes M2 polarization in both mouse and human macrophages, potentially compromising antitumor immune responses. By contrast, Stat6 mediates the suppression of TRIM24 expression in M2 macrophages to contribute to the induction of an immunosuppressive tumor niche. Taken together, our findings establish Stat6 acetylation as an essential negative regulatory mechanism that curtails macrophage M2 polarization.

STAT3 is constitutively acetylated on lysine 685 residues in chronic lymphocytic leukemia cells

Signal transducer and activator of transcription (STAT)-3 might be phosphorylated or acetylated. Unlike the phosphorylation of STAT3, little is known about the acetylation of STAT3 in chronic lymphocytic leukemia (CLL) cells. Because acetylation activates STAT3 transcription, we sought to study the acetylation status of STAT3 in CLL cells. Using Western immunoblotting, immunoprecipitation, and flow cytometry we found that, apart from its constitutive serine phosphorylation, STAT3 is constitutively acetylated on lysine 685 residues. Because the acetyltransferase p300 was found to acetylate STAT3 on lysine 685 residues, we wondered whether p300 acetylates STAT3 in CLL cells. Using Western immunoblotting we detected high levels of p300 protein in CLL but not normal B cells. Transfection of CLL cells with p300 small-interfering (si) RNA downregulated p300 transcripts as well as p300 and acetyl-STAT3 protein levels. In addition, p300 siRNA attenuated STAT3-DNA binding and downregulated mRNA levels of STAT3-regulated genes. Furthermore, transfection of CLL cells with p300-siRNA induced a 3-fold increase in the rate of spontaneous apoptosis. Taken together, our data suggest that in CLL cells STAT3 p300 induces constitutive acetylation and activation of STAT3. Whether inhibition of STAT3 acetylation might provide clinical benefit in patients with CLL remains to be determined.

Implications of STAT3 and STAT5 signaling on gene regulation and chromatin remodeling in hematopoietic cancer

STAT3 and STAT5 proteins are oncogenic downstream mediators of the JAK–STAT pathway. Deregulated STAT3 and STAT5 signaling promotes cancer cell proliferation and survival in conjunction with other core cancer pathways. Nuclear phosphorylated STAT3 and STAT5 regulate cell-type-specific transcription profiles via binding to promoter elements and exert more complex functions involving interaction with various transcriptional coactivators or corepressors and chromatin remodeling proteins. The JAK–STAT pathway can rapidly reshape the chromatin landscape upon cytokine, hormone, or growth factor stimulation and unphosphorylated STAT proteins also appear to be functional with respect to regulating chromatin accessibility. Notably, cancer genome landscape studies have implicated mutations in various epigenetic modifiers as well as the JAK–STAT pathway as underlying causes of many cancers, particularly acute leukemia and lymphomas. However, it is incompletely understood how mutations within these pathways can interact and synergize to promote cancer. We summarize the current knowledge of oncogenic STAT3 and STAT5 functions downstream of cytokine signaling and provide details on prerequisites for DNA binding and gene transcription. We also discuss key interactions of STAT3 and STAT5 with chromatin remodeling factors such as DNA methyltransferases, histone modifiers, cofactors, corepressors, and other transcription factors.

Regulation of T-Cell Signaling by Post-Translational Modifications in Autoimmune Disease

The adaptive immune system involves antigen-specific host defense mechanisms mediated by T and B cells. In particular, CD4⁺ T cells play a central role in the elimination of pathogens. Immunological tolerance in the thymus regulates T lymphocytes to avoid self-components, including induction of cell death in immature T cells expressing the self-reactive T-cell receptor repertoire. In the periphery, mature T cells are also regulated by tolerance, e.g., via induction of anergy or regulatory T cells. Thus, T cells strictly control intrinsic signal transduction to prevent excessive responses or self-reactions. If the inhibitory effects of T cells on these mechanisms are disrupted, T cells may incorrectly attack self-components, which can lead to autoimmune disease. The functions of T cells are supported by post-translational modifications, particularly phosphorylation, of signaling molecules, the proper regulation of which is controlled by endogenous mechanisms within the T cells themselves. In recent years, molecular targeted agents against kinases have been developed for treatment of autoimmune diseases. In this review, we discuss T-cell signal transduction in autoimmune disease and provide an overview of acetylation-mediated regulation of T-cell signaling pathways.

Lysine Acetylation Goes Global: From Epigenetics to Metabolism and Therapeutics

Post-translational acetylation of lysine residues has emerged as a key regulatory mechanism in all eukaryotic organisms. Originally discovered in 1963 as a unique modification of histones, acetylation marks are now found on thousands of nonhistone proteins located in virtually every cellular compartment. Here we summarize key findings in the field of protein acetylation over the past 20 years with a focus on recent discoveries in nuclear, cytoplasmic, and mitochondrial compartments. Collectively, these findings have elevated protein acetylation as a major post-translational modification, underscoring its physiological relevance in gene regulation, cell signaling, metabolism, and disease.

Pharmacologic inhibition of STAT5 in acute myeloid leukemia

The transcription factor STAT5 is an essential downstream mediator of many tyrosine kinases (TKs), particularly in hematopoietic cancers. STAT5 is activated by FLT3-ITD, which is a constitutively active TK driving the pathogenesis of acute myeloid leukemia (AML). Since STAT5 is a critical mediator of diverse malignant properties of AML cells, direct targeting of STAT5 is of significant clinical value. Here, we describe the development and preclinical evaluation of a novel, potent STAT5 SH2 domain inhibitor, AC-4–130, which can efficiently block pathological levels of STAT5 activity in AML. AC-4–130 directly binds to STAT5 and disrupts STAT5 activation, dimerization, nuclear translocation, and STAT5-dependent gene transcription. Notably, AC-4–130 substantially impaired the proliferation and clonogenic growth of human AML cell lines and primary FLT3-ITD⁺ AML patient cells in vitro and in vivo. Furthermore, AC-4–130 synergistically increased the cytotoxicity of the JAK1/2 inhibitor Ruxolitinib and the p300/pCAF inhibitor Garcinol. Overall, the synergistic effects of AC-4–130 with TK inhibitors (TKIs) as well as emerging treatment strategies provide new therapeutic opportunities for leukemia and potentially other cancers.

Opposing Roles of Acetylation and Phosphorylation in LIFR-Dependent Self-Renewal Growth Signaling in Mouse Embryonic Stem Cells

LIF promotes self-renewal of mouse embryonic stem cells (mESCs), and in its absence, the cells differentiate. LIF binds to the LIF receptor (LIFR) and activates the JAK-STAT3 pathway, but it remains unknown how the receptor complex triggers differentiation or self-renewal. Here, we report that the LIFR cytoplasmic domain contains a self-renewal domain within the juxtamembrane region and a differentiation domain within the C-terminal region. The differentiation domain contains four SPXX repeats that are phosphorylated by MAPK to restrict STAT3 activation; the self-renewal domain is characterized by a 3K motif that is acetylated by p300. In mESCs, acetyl-LIFR undergoes homodimerization, leading to STAT3 hypo- or hyper-activation depending on the presence or absence of gp130. LIFR-activated STAT3 restricts differentiation via cytokine induction. Thus, LIFR acetylation and serine phosphorylation differentially promote stem cell self-renewal and differentiation.

Role of influenza A virus NP acetylation on viral growth and replication

Lysine acetylation is a post-translational modification known to regulate protein functions. Here we identify several acetylation sites of the influenza A virus nucleoprotein (NP), including the lysine residues K77, K113 and K229. Viral growth of mutant virus encoding K229R, mimicking a non-acetylated NP lysine residue, is severely impaired compared to wildtype or the mutant viruses encoding K77R or K113R. This attenuation is not the result of decreased polymerase activity, altered protein expression or disordered vRNP co-segregation but rather caused by impaired particle release. Interestingly, release deficiency is also observed mimicking constant acetylation at this site (K229Q), whereas virus encoding NP-K113Q could not be generated. However, mimicking NP hyper-acetylation at K77 and K229 severely diminishes viral polymerase activity, while mimicking NP hypo-acetylation at these sites has no effect on viral replication. These results suggest that NP acetylation at K77, K113 and K229 impacts multiple steps in viral replication of influenza A viruses.

Post-translational modifications of influenza A virus proteins can regulate virus replication, but the effect of nucleoprotein (NP) acetylation is not known. Here, Giese et al. identify four NP lysine residues that are acetylated in infected cells and study their role in polymerase activity and virion release.

The complex roles of STAT3 and STAT5 in maintaining redox balance: Lessons from STAT-mediated xCT expression in cancer cells

STAT3 and STAT5 mediate diverse cellular processes, transcriptionally regulating gene expression and interacting with cytoplasmic proteins. Their canonical activity is stimulated by cytokines/growth factors through JAK-STAT signaling. As targets of oncogenes with intrinsic tyrosine kinase activity, STAT3 and STAT5 become constitutively active in hematologic neoplasms and solid tumors, promoting cell proliferation and survival and modulating redox homeostasis. This review summarizes reactive oxygen species (ROS)-regulated STAT activation and how STATs influence ROS production. ROS-induced effects on post-translational modifications are presented, and STAT3/5-mediated regulation of xCT, a redox-sensitive target up-regulated in numerous cancers, is discussed with regard to transcriptional cross-talk.

Inhibition of interleukin-3- and interferon- α-induced JAK/STAT signaling by the synthetic α-X-2′,3,4,4′-tetramethoxychalcones α-Br-TMC and α-CF3-TMC

The JAK/STAT pathway is an essential mediator of cytokine signaling, often upregulated in human diseases and therefore recognized as a relevant therapeutic target. We previously identified the synthetic chalcone α-bromo-2′,3,4,4′-tetramethoxychalcone (α-Br-TMC) as a novel JAK2/STAT5 inhibitor. We also found that treatment with α-Br-TMC resulted in a downward shift of STAT5 proteins in SDS-PAGE, suggesting a post-translational modification that might affect STAT5 function. In the present study, we show that a single cysteine within STAT5 is responsible for the α-Br-TMC-induced protein shift, and that this modification does not alter STAT5 transcriptional activity. We also compared the inhibitory activity of α-Br-TMC to that of another synthetic chalcone, α-trifluoromethyl-2′,3,4,4′-tetramethoxychalcone (α-CF3-TMC). We found that, like α-Br-TMC, α-CF3-TMC inhibits JAK2 and STAT5 phosphorylation in response to interleukin-3, however without altering STAT5 mobility in SDS-PAGE. Moreover, we demonstrate that both α-Br-TMC and α-CF3-TMC inhibit interferon-α-induced activation of STAT1 and STAT2, by inhibiting their phosphorylation and the expression of downstream interferon-stimulated genes. Together with the previous finding that α-Br-TMC and α-CF3-TMC inhibit the response to inflammation by inducing Nrf2 and blocking NF-κB activities, our data suggest that synthetic chalcones might be useful as anti-inflammatory, anti-cancer and immunomodulatory agents in the treatment of human diseases.

Prolactin receptor in breast cancer: marker for metastatic risk

Prolactin and prolactin receptor signaling and function are complex in nature and intricate in function. Basic, pre-clinical and translational research has opened up our eyes to the understanding that prolactin and prolactin receptor signaling function differently within different cellular contexts and microenvironmental conditions. Its multiple roles in normal physiology are subverted in cancer initiation and progression, and gradually we are teasing out the intricacies of function and therapeutic value. Recently, we observed that prolactin has a role in accelerating the time to bone metastasis in breast cancer patients and identified the mechanism by which prolactin stimulated breast cancer cell-mediated lytic osteoclast formation. The possibility that the prolactin receptor is a marker for metastasis, and specifically bone metastasis, is one that may have to be put into the context of the different variants of prolactin, different prolactin receptor isoforms and intricate signaling pathways that are regulated by the microenvironment. The more complete the picture, the better one can test biomarker identity and design clinical trials to test therapeutic intervention. This review will cover the recent advances and highlight the complexity of prolactin receptor biology.

Acetylation Modulates IL-2 Receptor Signaling in T Cells

Ligand binding to the cognate cytokine receptors activates intracellular signaling by recruiting protein tyrosine kinases and other protein modification enzymes. However, the roles of protein modifications other than phosphorylation remain unclear. In this study, we examine a novel regulatory mechanism of Stat5, based on its acetylation. As for phosphorylation, IL-2 induces the acetylation of signaling molecules, including Stat5, in the murine T cell line CTLL-2. Stat5 is acetylated in the cytoplasm by CREB-binding protein (CBP). Acetylated Lys⁶⁹⁶ and Lys⁷⁰⁰ on Stat5 are critical indicators for limited proteolysis, which leads to the generation of a truncated form of Stat5. In turn, the truncated form of Stat5 prevents transcription of the full-length form of Stat5. We also demonstrate that CBP physically associates with the IL-2 receptor β-chain. CBP, found in the nucleus in resting CTLL-2 cells, relocates to the cytoplasm after IL-2 stimulation in an MEK/ERK pathway-dependent manner. Thus, IL-2-mediated acetylation plays an important role in the modulation of cytokine signaling and T cell fate.

HDAC6 Deacetylates HMGN2 to Regulate Stat5a Activity and Breast Cancer Growth

Stat5a is a transcription factor utilized by several cytokine/hormone receptor signaling pathways that promotes transcription of genes associated with proliferation, differentiation, and survival of cancer cells. However, there are currently no clinically approved therapies that directly target Stat5a, despite ample evidence that it contributes to breast cancer pathogenesis. Here, deacetylation of the Stat5a coactivator and chromatin-remodeling protein HMGN2 on lysine residue K2 by HDAC6 promotes Stat5a-mediated transcription and breast cancer growth. HDAC6 inhibition both in vitro and in vivo enhances HMGN2 acetylation with a concomitant reduction in Stat5a-mediated signaling, resulting in an inhibition of breast cancer growth. Furthermore, HMGN2 is highly acetylated at K2 in normal human breast tissue, but is deacetylated in primary breast tumors and lymph node metastases, suggesting that targeting HMGN2 deacetylation is a viable treatment for breast cancer. Together, these results reveal a novel mechanism by which HDAC6 activity promotes the transcription of Stat5a target genes and demonstrate utility of HDAC6 inhibition for breast cancer therapy.

IMPLICATIONS

HMGN2 deacetylation enhances Stat5a transcriptional activity, thereby regulating prolactin-induced gene transcription and breast cancer growth. Mol Cancer Res; 14(10); 994-1008. ©2016 AACR.

Prolactin protects retinal pigment epithelium by inhibiting sirtuin 2-dependent cell death

The identification of pathways necessary for retinal pigment epithelium (RPE) function is fundamental to uncover therapies for blindness. Prolactin (PRL) receptors are expressed in the retina, but nothing is known about the role of PRL in RPE. Using the adult RPE 19 (ARPE-19) human cell line and mouse RPE, we identified the presence of PRL receptors and demonstrated that PRL is necessary for RPE cell survival via anti-apoptotic and antioxidant actions. PRL promotes the antioxidant capacity of ARPE-19 cells by reducing glutathione. It also blocks the hydrogen peroxide-induced increase in deacetylase sirtuin 2 (SIRT2) expression, which inhibits the TRPM2-mediated intracellular Ca(2+) rise associated with reduced survival under oxidant conditions. RPE from PRL receptor-null (prlr(-/-)) mice showed increased levels of oxidative stress, Sirt2 expression and apoptosis, effects that were exacerbated in animals with advancing age. These observations identify PRL as a regulator of RPE homeostasis.

Aberrant lysine acetylation in tumorigenesis: Implications in the development of therapeutics

The 'language' of covalent histone modifications translates environmental and cellular cues into gene expression. This vast array of post-translational modifications on histones are more than just covalent moieties added onto a protein, as they also form a platform on which crucial cellular signals are relayed. The reversible lysine acetylation has emerged as an important post-translational modification of both histone and non-histone proteins, dictating numerous epigenetic programs within a cell. Thus, understanding the complex biology of lysine acetylation and its regulators is essential for the development of epigenetic therapeutics. In this review, we will attempt to address the complexities of lysine acetylation in the context of tumorigenesis, their role in cancer progression and emphasize on the modalities developed to target lysine acetyltransferases towards cancer treatment.

New Insights into the Role of Histone Deacetylases as Coactivators of Inflammatory Gene Expression

SIGNIFICANCE

The expression and/or activity of histone deacetylases (HDACs) can be regulated by a variety of environmental conditions, including inflammation and oxidative stress. These events result in diminished or exaggerated protein acetylation, both of which can be causative for many ailments. While the anti-inflammatory activity of HDAC inhibitors (HDACis) is well known, recent studies started unraveling details of the molecular mechanisms underlying the pro-inflammatory function of HDACs.

RECENT ADVANCES

Recent evidence shows that HDACs are found in association with transcribed regions and ensure proper transcription by maintaining acetylation homeostasis. We also discuss current insights in the molecular mechanisms mediating acetylation-dependent inhibition of pro-inflammatory transcription factors of the NF-κB, HIF-1, IRF, and STAT families.

CRITICAL ISSUES

The high number of acetylations and the complexity of the regulatory consequences make it difficult to assign biological effects directly to a single acetylation event. The vast majority of acetylated proteins are nonhistone proteins, and it remains to be shown whether the therapeutic effects of HDACis are attributable to altered histone acetylation.

FUTURE DIRECTIONS

In the traditional view, only exaggerated acetylation is harmful and causative for diseases. Recent data show the relevance of acetylation homeostasis and suggest that both diminished and inflated acetylation can enable the development of ailments. Since acetylation of nonhistone proteins is essential for the induction of a substantial part of the inflammatory gene expression program, HDACis are more than "epigenetic drugs." The identification of substrates for individual HDACs will be the prerequisite for the adequate use of highly specific HDACis.

Deacetylase inhibitors repress STAT5-mediated transcription by interfering with bromodomain and extra-terminal (BET) protein function

Signal transducer and activator of transcription STAT5 is essential for the regulation of proliferation and survival genes. Its activity is tightly regulated through cytokine signaling and is often upregulated in cancer. We showed previously that the deacetylase inhibitor trichostatin A (TSA) inhibits STAT5-mediated transcription by preventing recruitment of the transcriptional machinery at a step following STAT5 binding to DNA. The mechanism and factors involved in this inhibition remain unknown. We now show that deacetylase inhibitors do not target STAT5 acetylation, as we initially hypothesized. Instead, they induce a rapid increase in global histone acetylation apparently resulting in the delocalization of the bromodomain and extra-terminal (BET) protein Brd2 and of the Brd2-associated factor TBP to hyperacetylated chromatin. Treatment with the BET inhibitor (+)-JQ1 inhibited expression of STAT5 target genes, supporting a role of BET proteins in the regulation of STAT5 activity. Accordingly, chromatin immunoprecipitation demonstrated that Brd2 is associated with the transcriptionally active STAT5 target gene Cis and is displaced upon TSA treatment. Our data therefore indicate that Brd2 is required for the proper recruitment of the transcriptional machinery at STAT5 target genes and that deacetylase inhibitors suppress STAT5-mediated transcription by interfering with Brd2 function.

The natural chemopreventive agent sulforaphane inhibits STAT5 activity

Signal transducer and activator of transcription STAT5 is an essential mediator of cytokine, growth factor and hormone signaling. While its activity is tightly regulated in normal cells, its constitutive activation directly contributes to oncogenesis and is associated to a number of hematological and solid tumor cancers. We previously showed that deacetylase inhibitors can inhibit STAT5 transcriptional activity. We now investigated whether the dietary chemopreventive agent sulforaphane, known for its activity as deacetylase inhibitor, might also inhibit STAT5 activity and thus could act as a chemopreventive agent in STAT5-associated cancers. We describe here sulforaphane (SFN) as a novel STAT5 inhibitor. We showed that SFN, like the deacetylase inhibitor trichostatin A (TSA), can inhibit expression of STAT5 target genes in the B cell line Ba/F3, as well as in its transformed counterpart Ba/F3-1*6 and in the human leukemic cell line K562 both of which express a constitutively active form of STAT5. Similarly to TSA, SFN does not alter STAT5 initial activation by phosphorylation or binding to the promoter of specific target genes, in favor of a downstream transcriptional inhibitory effect. Chromatin immunoprecipitation assays revealed that, in contrast to TSA however, SFN only partially impaired the recruitment of RNA polymerase II at STAT5 target genes and did not alter histone H3 and H4 acetylation, suggesting an inhibitory mechanism distinct from that of TSA. Altogether, our data revealed that the natural compound sulforaphane can inhibit STAT5 downstream activity, and as such represents an attractive cancer chemoprotective agent targeting the STAT5 signaling pathway.

The synthetic α-bromo-2',3,4,4'-tetramethoxychalcone (α-Br-TMC) inhibits the JAK/STAT signaling pathway

Signal transducer and activator of transcription STAT5 and its upstream activating kinase JAK2 are essential mediators of cytokine signaling. Their activity is normally tightly regulated and transient. However, constitutive activation of STAT5 is found in numerous cancers and a driving force for malignant transformation. We describe here the identification of the synthetic chalcone α-Br-2′,3,4,4′-tetramethoxychalcone (α-Br-TMC) as a novel JAK/STAT inhibitor. Using the non-transformed IL-3-dependent B cell line Ba/F3 and its oncogenic derivative Ba/F3-1*6 expressing constitutively activated STAT5, we show that α-Br-TMC targets the JAK/STAT pathway at multiple levels, inhibiting both JAK2 and STAT5 phosphorylation. Moreover, α-Br-TMC alters the mobility of STAT5A/B proteins in SDS-PAGE, indicating a change in their post-translational modification state. These alterations correlate with a decreased association of STAT5 and RNA polymerase II with STAT5 target genes in chromatin immunoprecipitation assays. Interestingly, expression of STAT5 target genes such as Cis and c-Myc was differentially regulated by α-Br-TMC in normal and cancer cells. While both genes were inhibited in IL-3-stimulated Ba/F3 cells, expression of the oncogene c-Myc was down-regulated and that of the tumor suppressor gene Cis was up-regulated in transformed Ba/F3-1*6 cells. The synthetic chalcone α-Br-TMC might therefore represent a promising novel anticancer agent for therapeutic intervention in STAT5-associated malignancies.

Histone deacetylases: a saga of perturbed acetylation homeostasis in cancer

In the current era of genomic medicine, diseases are identified as manifestations of anomalous patterns of gene expression. Cancer is the principal example among such maladies. Although remarkable progress has been achieved in the understanding of the molecular mechanisms involved in the genesis and progression of cancer, its epigenetic regulation, particularly histone deacetylation, demands further studies. Histone deacetylases (HDACs) are one of the key players in the gene expression regulation network in cancer because of their repressive role on tumor suppressor genes. Higher expression and function of deacetylases disrupt the finely tuned acetylation homeostasis in both histone and non-histone target proteins. This brings about alterations in the genes implicated in the regulation of cell proliferation, differentiation, apoptosis and other cellular processes. Moreover, the reversible nature of epigenetic modulation by HDACs makes them attractive targets for cancer remedy. This review summarizes the current knowledge of HDACs in tumorigenesis and tumor progression as well as their contribution to the hallmarks of cancer. The present report also describes briefly various assays to detect histone deacetylase activity and discusses the potential role of histone deacetylase inhibitors as emerging epigenetic drugs to cure cancer.

Acetylation and sumoylation control STAT5 activation antagonistically

STAT5 proteins are activated by tyrosine phosphorylation, but recently further post-translation modifications such as serine/threonine phosphorylation, acetylation at lysine residues or sumoylation in close vicinity of the critical tyrosine residue have been reported. Here, we discuss new findings on impaired STAT5 signaling in lymphocytes isolated from a SUMO-specific protease knockout mouse (SENP1^−/−), which results in sumoylated STAT5 and abolishes tyrosine phosphorylation. Van Nguyen and colleagues examined acetylation and sumoylation of STAT5 and found that both modifications act antagonistically to control tyrosine phosphorylation of STAT5.

PRLR regulates hepatic insulin sensitivity in mice via STAT5

Insulin resistance is one of the major contributing factors in the development of metabolic diseases. The mechanisms responsible for insulin resistance, however, remain poorly understood. Although numerous functions of the prolactin receptor (PRLR) have been identified, a direct effect on insulin sensitivity has not been previously described. The aim of our current study is to investigate this possibility and elucidate underlying mechanisms. Here we show that insulin sensitivity is improved or impaired in mice injected with adenovirus that overexpress or knock down PRLR expression, respectively. Similar observations were obtained in in vitro studies. In addition, we discovered that the signal transducer and activator of transcription-5 pathway are required for regulating insulin sensitivity by PRLR. Moreover, we observed that PRLR expression is decreased or increased under insulin-resistant (db/db mice) or insulin-sensitive (leucine deprivation) conditions, respectively, and found that altering PRLR expression significantly reverses insulin sensitivity under both conditions. Finally, we found that PRLR expression levels are increased under leucine deprivation via a general control nonderepressible 2/mammalian target of rapamycin/ribosomal protein S6 kinase-1-dependent pathway. These results demonstrate a novel function for hepatic PRLR in the regulation of insulin sensitivity and provide important insights concerning the nutritional regulation of PRLR expression.

SIRT1 regulates adaptive response of the growth hormone--insulin-like growth factor-I axis under fasting conditions in liver

Adaptation under fasting conditions is critical for survival in animals. Sirtuin 1 (SIRT1), a protein deacetylase, plays an essential role in adaptive metabolic and endocrine responses under fasting conditions by modifying the acetylation status of various proteins. Fasting induces growth hormone (GH) resistance in the liver, leading to decreased serum insulin-like growth factor-I (IGF-I) levels as an endocrine adaptation for malnutrition; however, the underlying mechanisms of this action remain to be fully elucidated. Here we report that in vivo knockdown of SIRT1 in the liver restored the fasting-induced decrease in serum IGF-I levels and enhanced the GH-dependent increase in IGF-I levels, indicating that SIRT1 negatively regulates GH-dependent IGF-I production in the liver. In vitro analysis using hepatocytes demonstrated that SIRT1 suppresses GH-dependent IGF-I expression, accompanied by decreased tyrosine phosphorylation on signal transducer and activator of transcription (STAT) 5. GST pull-down assays revealed that SIRT1 interacts directly with STAT5. When the lysine residues adjacent to the SH2 domain of STAT5 were mutated, STAT5 acetylation decreased concomitant with a decrease in its transcriptional activity. Knockdown of SIRT1 enhanced the acetylation and GH-induced tyrosine phosphorylation of STAT5, as well as the GH-induced interaction of the GH receptor with STAT5. These data indicate that SIRT1 negatively regulates GH-induced STAT5 phosphorylation and IGF-I production via deacetylation of STAT5 in the liver. In addition, our findings explain the underlying mechanisms of GH resistance under fasting conditions, which is a known element of endocrine adaptation during fasting.

STAT5 acetylation: Mechanisms and consequences for immunological control and leukemogenesis

The cytokine-inducible transcription factors signal transducer and activator of transcription 5A and 5B (STAT5A and STAT5B) are important for the proper development of multicellular eukaryotes. Disturbed signaling cascades evoking uncontrolled expression of STAT5 target genes are associated with cancer and immunological failure. Here, we summarize how STAT5 acetylation is integrated into posttranslational modification networks within cells. Moreover, we focus on how inhibitors of deacetylases and tyrosine kinases can correct leukemogenic signaling nodes involving STAT5. Such small molecules can be exploited in the fight against neoplastic diseases and immunological disorders.

Regulation of STAT signaling by acetylation

Signal transducers and activators of transcription (STAT) belong to a family of latent cytoplasmic factors that can be activated by tyrosine phosphorylation by the members of the Jak tyrosine kinase family in response to a variety of cytokines and growth factors. Activated STATs form dimers and translocate into nucleus to induce expression of critical genes essential for normal cellular events. In the past several years, significant progress has been made in the characterization of STAT acetylation, which is dependent on the balance between histone deacetylases (HDACs) and histone acetyltransferases (HATs) such as CBP/p300. Acetylation of STAT1, STAT2, STAT3, STAT5b and STAT6 has been identified. This review will highlight acetylation on the modulation of STAT activation.

Blocking the class I histone deacetylase ameliorates renal fibrosis and inhibits renal fibroblast activation via modulating TGF-beta and EGFR signaling

BACKGROUND

Histone deacetylase (HDAC) inhibitors are promising anti-fibrosis drugs; however, nonselective inhibition of class I and class II HDACs does not allow a detailed elucidation of the individual HDAC functions in renal fibrosis. In this study, we investigated the effect of MS-275, a selective class I HDAC inhibitor, on the development of renal fibrosis in a murine model of unilateral ureteral obstruction (UUO) and activation of cultured renal interstitial fibroblasts.

METHODS/FINDINGS

The UUO model was established by ligation of the left ureter and the contralateral kidney was used as a control. At seven days after UUO injury, kidney developed fibrosis as indicated by deposition of collagen fibrils and increased expression of collagen I, fibronectin and alpha-smooth muscle actin (alpha-SMA). Administration of MS-275 inhibited all these fibrotic responses and suppressed UUO-induced production of transforming growth factor-beta1 (TGF-beta), increased expression of TGF-beta receptor I, and phosphorylation of Smad-3. MS-275 was also effective in suppressing phosphorylation and expression of epidermal growth factor receptor (EGFR) and its downstream signaling molecule, signal transducer and activator of transcription-3. Moreover, class I HDAC inhibition reduced the number of renal tubular cells arrested in the G2/M phase of the cell cycle, a cellular event associated with TGF-beta1overproduction. In cultured renal interstitial fibroblasts, MS-275 treatment inhibited TGF-beta induced phosphorylation of Smad-3, differentiation of renal fibroblasts to myofibroblasts and proliferation of myofibroblasts.

CONCLUSIONS AND SIGNIFICANCE

These results demonstrate that class I HDACs are critically involved in renal fibrogenesis and renal fibroblast activation through modulating TGF-beta and EGFR signaling and suggest that blockade of class I HDAC may be a useful treatment for renal fibrosis.

Acetylation of endogenous STAT proteins

Acetylation of signal transducer and activator of transcription (STAT) proteins has been recognized as a significant mechanism for the regulation of their cellular functions. Site-specific antibodies are available only for a minority of STATs. The detection of acetylated STATs by immunoprecipitation (IP) followed by western blot (WB) will be described in the following chapter. Defined conditions for cell lysis and IP will be elucidated on the basis of STAT1 acetylation.

The HAT/HDAC interplay: multilevel control of STAT signaling

Besides the transcription-promoting role of histone acetyltransferases (HATs) and the transcription-delimiting function of histone deacetylases (HDACs) through histone acetylation and deacetylation respectively, HATs and HDACs also regulate the activity of several non-histone proteins. This includes signal transducers and activators of transcription (STATs), key proteins in cytokine signaling. Unlike Tyr phosphorylation/dephosphorylation, which mainly acts as an on/off switch of STAT activity, the control exerted by HATs and HDACs appears multifaceted and far more complex than initially imagined. Our review focuses on the latest trends and novel hypotheses to explain differential context-dependent STAT regulation by complex posttranslational modification patterns. We chart the knowledge on how STATs interact with HATs and HDACs, and additionally bring a transcriptional regulatory and gene-set specific role for HDACs in the picture. Indeed, a growing amount of evidence demonstrates, paradoxically, that not only HAT but also HDAC activity can be required for STAT-dependent transcription, in a STAT subtype- and cell type-dependent manner. Referring to recent reports, we review and discuss the various molecular mechanisms that have recently been proposed to account for this peculiar regulation, in an attempt to shed more light on the difficult yet important question on how STAT specificity is being generated.

Molecular mechanisms of prolactin and its receptor

Prolactin and the prolactin receptors are members of a family of hormone/receptor pairs which include GH, erythropoietin, and other ligand/receptor pairs. The mechanisms of these ligand/receptor pairs have broad similarities, including general structures, ligand/receptor stoichiometries, and activation of several common signaling pathways. But significant variations in the structural and mechanistic details are present among these hormones and their type 1 receptors. The prolactin receptor is particularly interesting because it can be activated by three sequence-diverse human hormones: prolactin, GH, and placental lactogen. This system offers a unique opportunity to compare the detailed molecular mechanisms of these related hormone/receptor pairs. This review critically evaluates selected literature that informs these mechanisms, compares the mechanisms of the three lactogenic hormones, compares the mechanism with those of other class 1 ligand/receptor pairs, and identifies information that will be required to resolve mechanistic ambiguities. The literature describes distinct mechanistic differences between the three lactogenic hormones and their interaction with the prolactin receptor and describes more significant differences between the mechanisms by which other related ligands interact with and activate their receptors.

Histone deacetylases 6 and 9 and sirtuin-1 control Foxp3+ regulatory T cell function through shared and isoform-specific mechanisms

Therapeutic inhibition of the histone deacetylases HDAC6, HDAC9, or sirtuin-1 (Sirt1) augments the suppressive functions of regulatory T cells (T(regs)) that contain the transcription factor Foxp3 (Forkhead box P3) and is useful in organ transplant patients or patients with autoimmune diseases. However, it is unclear whether distinct mechanisms are involved for each HDAC or whether combined inhibition of HDACs would be more effective. We compared the suppressive functions of T(regs) from wild-type C57BL/6 mice with those from mice with either complete or cell-specific deletion of various HDACs, as well as with those of T(regs) treated with isoform-selective HDAC inhibitors. The improvement of T(reg) suppressive function mediated by inhibition of HDAC6, but not Sirt1, required an intact heat shock response. Although HDAC6, HDAC9, and Sirt1 all deacetylated Foxp3, each protein had different effects on transcription factors that control expression of the gene encoding Foxp3. For example, loss of HDAC9, but not other HDACs, was associated with stabilization of the acetylated form of signal transducer and activator of transcription 5 (STAT5) and promoted its transcriptional activity. Thus, targeting different HDACs increased T(reg) function through multiple and additive mechanisms, which suggests the therapeutic potential for using combinations of HDAC inhibitors in the management of autoimmunity and organ transplantation.

Prolactin signaling mechanisms in ovary

Prolactin is a hormone that is essential for normal reproduction and signals through two types of receptors. Not only is the classical long form of the prolactin receptor identified, but so are many short form receptors in rodents and human tissues. Mouse mutagenesis studies have offered insight into the biology of prolactin family, providing compelling evidence that the different isoforms have independent biological activity. The possibility that short forms mediate cell proliferation is important for a variety of tissues including mammary gland and ovarian follicles. This review summarizes our current knowledge about prolactin signaling and its role in reproduction through either long or short isoform receptors.

Sirtuin biology and relevance to diabetes treatment

Sirtuins are a group of NAD(+)-dependent enzymes that post-translationally modify histones and other proteins. Among seven mammalian sirtuins, SIRT1 has been the most extensively studied and has been demonstrated to play a critical role in all major metabolic organs and tissues. SIRT1 regulates glucose and lipid homeostasis in the liver, modulates insulin secretion in pancreatic islets, controls insulin sensitivity and glucose uptake in skeletal muscle, increases adiponectin expression in white adipose tissue and controls food intake and energy expenditure in the brain. Recently, SIRT3 has been demonstrated to modulate insulin sensitivity in skeletal muscle and systemic metabolism, and Sirt3-null mice manifest characteristics of metabolic syndrome on a high-fat diet. Thus, it is reasonable to believe that enhancing the activities of SIRT1 and SIRT3 may be beneficial for Type 2 diabetes. Although it is controversial, the SIRT1 activator SRT1720 has been reported to be effective in improving glucose metabolism and insulin sensitivity in animal models. More research needs to be conducted so that we can better understand the physiological functions and molecular mechanisms of sirtuins in order to therapeutically target these enzymes for diabetes treatment.

SUMO-specific protease 1 is critical for early lymphoid development through regulation of STAT5 activation

Small ubiquitin-like modifier (SUMO) modification has emerged as an important regulatory mechanism during embryonic development. However, it is not known whether SUMOylation plays a role in the development of the immune system. Here, we show that SUMO-specific protease 1 (SENP1) is essential for the development of early T and B cells. STAT5, a key regulator of lymphoid development, is modified by SUMO-2 and is specifically regulated by SENP1. In the absence of SENP1, SUMO-2 modified STAT5 accumulates in early lymphoid precursors, resulting in a block in its acetylation and subsequent signaling. These results demonstrate a crucial role of SENP1 in the regulation of STAT5 activation during early lymphoid development.

Nanoscale membrane organization: where biochemistry meets advanced microscopy

Understanding the molecular mechanisms that shape an effective cellular response is a fundamental question in biology. Biochemical measurements have revealed critical information about the order of protein-protein interactions along signaling cascades but lack the resolution to determine kinetics and localization of interactions on the plasma membrane. Furthermore, the local membrane environment influences membrane receptor distributions and dynamics, which in turn influences signal transduction. To measure dynamic protein interactions and elucidate the consequences of membrane architecture interplay, direct measurements at high spatiotemporal resolution are needed. In this review, we discuss the biochemical principles regulating membrane nanodomain formation and protein function, ranging from the lipid nanoenvironment to the cortical cytoskeleton. We also discuss recent advances in fluorescence microscopy that are making it possible to quantify protein organization and biochemical events at the nanoscale in the living cell membrane.