Vitamin D Switches BAF Complexes to Protect ß Cells.

A primary cause of disease progression in type 2 diabetes (T2D) is ß cell dysfunction due to inflammatory stress and insulin resistance. However, preventing ß cell exhaustion under diabetic conditions is a major therapeutic challenge. Here, we identify the vitamin D receptor (VDR) as a key modulator of inflammation and ß cell survival. Alternative recognition of an acetylated lysine in VDR by bromodomain proteins BRD7 and BRD9 directs association to PBAF and BAF chromatin remodeling complexes, respectively. Mechanistically, ligand promotes VDR association with PBAF to effect genome-wide changes in chromatin accessibility and enhancer landscape, resulting in an anti-inflammatory response. Importantly, pharmacological inhibition of BRD9 promotes PBAF-VDR association to restore ß cell function and ameliorate hyperglycemia in murine T2D models. These studies reveal an unrecognized VDR-dependent transcriptional program underpinning ß cell survival and identifies the VDR:PBAF/BAF association as a potential therapeutic target for T2D.

FXR mediates ILC-intrinsic responses to intestinal inflammation.

The pleiotropic actions of the Farnesoid X Receptor (FXR) are required for gut health, and reciprocally, reduced intestinal FXR signaling is seen in inflammatory bowel diseases (IBDs). Here, we show that activation of FXR selectively in the intestine is protective in inflammation-driven models of IBD. Prophylactic activation of FXR restored homeostatic levels of pro-inflammatory cytokines, most notably IL17. Importantly, these changes were attributed to FXR regulation of innate lymphoid cells (ILCs), with both the inflammation-driven increases in ILCs, and ILC3s in particular, and the induction of Il17a and Il17f in ILC3s blocked by FXR activation. Moreover, a population of ILC precursor-like cells increased with treatment, implicating FXR in the maturation/differentiation of ILC precursors. These findings identify FXR as an intrinsic regulator of intestinal ILCs and a potential therapeutic target in inflammatory intestinal diseases.

Metabolic control of regulatory T cell (Treg) survival and function by Lkb1.

The metabolic programs of functionally distinct T cell subsets are tailored to their immunologic activities. While quiescent T cells use oxidative phosphorylation (OXPHOS) for energy production, and effector T cells (Teffs) rely on glycolysis for proliferation, the distinct metabolic features of regulatory T cells (Tregs) are less well established. Here we show that the metabolic sensor LKB1 is critical to maintain cellular metabolism and energy homeostasis in Tregs. Treg-specific deletion of Lkb1 in mice causes loss of Treg number and function, leading to a fatal, early-onset autoimmune disorder. Tregs lacking Lkb1 have defective mitochondria, compromised OXPHOS, depleted cellular ATP, and altered cellular metabolism pathways that compromise their survival and function. Furthermore, we demonstrate that the function of LKB1 in Tregs is largely independent of the AMP-activated protein kinase, but is mediated by the MAP/microtubule affinity-regulating kinases and salt-inducible kinases. Our results define a metabolic checkpoint in Tregs that couples metabolic regulation to immune homeostasis and tolerance.

Stromal cues regulate the pancreatic cancer epigenome and metabolome.

A fibroinflammatory stromal reaction cooperates with oncogenic signaling to influence pancreatic ductal adenocarcinoma (PDAC) initiation, progression, and therapeutic outcome, yet the mechanistic underpinning of this crosstalk remains poorly understood. Here we show that stromal cues elicit an adaptive response in the cancer cell including the rapid mobilization of a transcriptional network implicated in accelerated growth, along with anabolic changes of an altered metabolome. The close overlap of stroma-induced changes in vitro with those previously shown to be regulated by oncogenic Kras in vivo suggests that oncogenic Kras signaling-a hallmark and key driver of PDAC-is contingent on stromal inputs. Mechanistically, stroma-activated cancer cells show widespread increases in histone acetylation at transcriptionally enhanced genes, implicating the PDAC epigenome as a presumptive point of convergence between these pathways and a potential therapeutic target. Notably, inhibition of the bromodomain and extraterminal (BET) family of epigenetic readers, and of Bromodomain-containing protein 2 (BRD2) in particular, blocks stroma-inducible transcriptional regulation in vitro and tumor progression in vivo. Our work suggests the existence of a molecular "AND-gate" such that tumor activation is the consequence of mutant Kras and stromal cues, providing insight into the role of the tumor microenvironment in the origin and treatment of Ras-driven tumors.

HIV-1 Tat and host AFF4 recruit two transcription elongation factors into a bifunctional complex for coordinated activation of HIV-1 transcription.

Recruitment of the P-TEFb kinase by HIV-1 Tat to the viral promoter triggers the phosphorylation and escape of RNA polymerase II from promoter-proximal pausing. It is unclear, however, if Tat recruits additional host factors that further stimulate HIV-1 transcription. Using a sequential affinity-purification scheme, we have identified human transcription factors/coactivators AFF4, ENL, AF9, and elongation factor ELL2 as components of the Tat-P-TEFb complex. Through the bridging functions of Tat and AFF4, P-TEFb and ELL2 combine to form a bifunctional elongation complex that greatly activates HIV-1 transcription. Without Tat, AFF4 can mediate the ELL2-P-TEFb interaction, albeit inefficiently. Tat overcomes this limitation by bringing more ELL2 to P-TEFb and stabilizing ELL2 in a process that requires active P-TEFb. The ability of Tat to enable two different classes of elongation factors to cooperate and coordinate their actions on the same polymerase enzyme explains why Tat is such a powerful activator of HIV-1 transcription.

A La-related protein modulates 7SK snRNP integrity to suppress P-TEFb-dependent transcriptional elongation and tumorigenesis.

The general transcription factor P-TEFb stimulates RNA polymerase II elongation and cotranscriptional processing of pre-mRNA. Contributing to a functional equilibrium important for growth control, a reservoir of P-TEFb is maintained in an inactive snRNP where 7SK snRNA is a central scaffold. Here, we identify PIP7S as a La-related protein stably associated with and required for 7SK snRNP integrity. PIP7S binds and stabilizes nearly all the nuclear 7SK via 3' -UUU-OH, leading to the sequestration and inactivation of P-TEFb. This function requires its La domain and intact C terminus. The latter is frequently deleted in human tumors due to microsatellite instability-associated mutations. Consistent with the tumor suppressor role of a Drosophila homolog of PIP7S, loss of PIP7S function shifts the P-TEFb equilibrium toward the active state, disrupts epithelial differentiation, and causes P-TEFb-dependent malignant transformation. Through PIP7S modulation of P-TEFb, our data thus link a general elongation factor to growth control and tumorigenesis.

HIV-1 Tat recruits transcription elongation factors dispersed along a flexible AFF4 scaffold.

The HIV-1 Tat protein stimulates viral gene expression by recruiting human transcription elongation complexes containing P-TEFb, AFF4, ELL2, and ENL or AF9 to the viral promoter, but the molecular organization of these complexes remains unknown. To establish the overall architecture of the HIV-1 Tat elongation complex, we mapped the binding sites that mediate complex assembly in vitro and in vivo. The AFF4 protein emerges as the central scaffold that recruits other factors through direct interactions with short hydrophobic regions along its structurally disordered axis. Direct binding partners CycT1, ELL2, and ENL or AF9 act as bridging components that link this complex to two major elongation factors, P-TEFb and the PAF complex. The unique scaffolding properties of AFF4 allow dynamic and flexible assembly of multiple elongation factors and connect the components not only to each other but also to a larger network of transcriptional regulators.

Human Polymerase-Associated Factor complex (PAFc) connects the Super Elongation Complex (SEC) to RNA polymerase II on chromatin.

The Super Elongation Complex (SEC), containing transcription elongation activators/coactivators P-TEFb, ELL2, AFF4/1, ENL, and AF9, is recruited by HIV-1 Tat and mixed lineage leukemia (MLL) proteins to activate the expression of HIV-1 and MLL-target genes, respectively. In the absence of Tat and MLL, however, it is unclear how SEC is targeted to RNA polymerase (Pol) II to stimulate elongation in general. Furthermore, although ENL and AF9 can bind the H3K79 methyltransferase Dot1L, it is unclear whether these bindings are required for SEC-mediated transcription. Here, we show that the homologous ENL and AF9 exist in separate SECs with similar but nonidentical functions. ENL/AF9 contacts the scaffolding protein AFF4 that uses separate domains to recruit different subunits into SEC. ENL/AF9 also exists outside SEC when bound to Dot1L, which is found to inhibit SEC function. The YEATS domain of ENL/AF9 targets SEC to Pol II on chromatin through contacting the human Polymerase-Associated Factor complex (PAFc) complex. This finding explains the YEATS domain's dispensability for leukemogenesis when ENL/AF9 is translocated to MLL, whose interactions with PAFc and DNA likely substitute for the PAFc/chromatin-targeting function of the YEATS domain.

HHLA2: An Emerging Immune Checkpoint for Cancer Immunotherapy.

HHLA2, a member of the B7 family of co-signaling molecules, is aberrantly expressed in various human cancers and has emerged as a promising target for cancer immunotherapy. It exhibits a unique structure and tissue distribution pattern compared to other B7 family members, where its expression is regulated by the complex physiological and tumor microenvironment. HHLA2 plays a crucial but contradictory role in immune modulation, and is thereby associated with heterogeneous prognostic implications across different cancer types. It interacts with two distinct receptors: TMIGD2, which is predominantly expressed on naïve T and NK cells to deliver co-stimulatory signals to T cells and NK cells; and KIR3DL3, which is prevalent on terminally differentiated T and CD56dim CD16+ NK cells to transmit inhibitory signals. The expression dynamics of these receptors on immune cells contribute to the maintenance of immune response homeostasis. Therapeutic strategies targeting the HHLA2 immune checkpoint aim to selectively inhibit the immunosuppressive HHLA2-KIR3DL3 pathway while preserving the HHLA2-TMIGD2 signaling. Several anti-HHLA2 and anti-KIR3DL3 antibodies are currently under investigation in early clinical trials, building upon encouraging results observed in humanized mouse models. Notably, the non-overlapping expression of HHLA2 and PD-L1 in tumors suggests potential synergistic benefits of combining HHLA2-KIR3DL3 targeted therapies with PD-1/PD-L1 blockade or anti-CTLA-4 to augment antitumor activity.

Purification and characterization of HIV-human protein complexes.

To fully understand how pathogens infect their host and hijack key biological processes, systematic mapping of intra-pathogenic and pathogen-host protein-protein interactions (PPIs) is crucial. Due to the relatively small size of viral genomes (usually around 10-100 proteins), generation of comprehensive host-virus PPI maps using different experimental platforms, including affinity tag purification-mass spectrometry (AP-MS) and yeast two-hybrid (Y2H) approaches, can be achieved. Global maps such as these provide unbiased insight into the molecular mechanisms of viral entry, replication and assembly. However, to date, only two-hybrid methodology has been used in a systematic fashion to characterize viral-host protein-protein interactions, although a deluge of data exists in databases that manually curate from the literature individual host-pathogen PPIs. We will summarize this work and also describe an AP-MS platform that can be used to characterize viral-human protein complexes and discuss its application for the HIV genome.

Antagonistic Antibody Targeting TNFR2 Inhibits Regulatory T Cell Function to Promote Anti-Tumor Activity.

Infiltration of regulatory T cells (Tregs) in the tumor microenvironment suppresses anti-tumor immune response, and promotes tumor progression. Tumor necrosis factor receptor-2 (TNFR2), which is highly expressed on Tregs, activates Tregs through nuclear factor kappa B (NF-κB) pathway. Moreover, TNFR2+ Tregs have been shown to be most suppressive among all Tregs populations in tumor. Due to the unique expression pattern and function of TNFR2 on Tregs, a TNFR2 blocking antibody is expected to compromise Tregs function, relieve Tregs-mediated immunosuppression, and hence to enhance anti-tumor immune response. AN3025 is an antagonistic anti-human TNFR2 (hTNFR2) antibody that is currently under preclinical development. This study investigates the immunomodulatory and anti-tumor activity of AN3025. AN3025 was generated through rabbit immunization with extracellular domain of human TNFR2 and subsequent humanization by complementarity-determining regions (CDRs) grafting. AN3025 binds to the extracellular domain of both human and cynomolgus with sub-nanomolar affinity and specificity, but not mouse or rat TNFR2. AN3025 inhibited tumor necrosis factor alpha (TNFα) induced cell death of hTNFR2-overexpressing Jurkat cells by competing with TNFα for binding to hTNFR2. In the Tregs/T effector co-culture assay, AN3025 increased T effector proliferation and enhanced interferon gamma (IFNγ) production. As a monotherapy, AN3025 significantly inhibited MC38 tumor growth in TNFR2 humanized mouse model. Subsequent flow cytometry (FACS) and immunohistochemistry (IHC) analysis revealed that administration of AN3025 led to decreased Tregs population, increased CD4+ and CD8+ T cell numbers in the tumor. The anti-tumor activity of AN3025 was dependent on the existence of CD4+ and CD8+ T cells, as depletion of CD4+ and CD8+ T cells abolished the anti-tumor activity of AN3025. In addition, AN3025 in combination with anti-PD-1 antibody demonstrated stronger in-vivo anti-tumor activity. The potent anti-tumor efficacy of AN3025, either as a monotherapy or in combination with anti-PD-1 antibody, supports its further clinical development for the treatment of various human tumors.

Modulation of a P-TEFb functional equilibrium for the global control of cell growth and differentiation.

P-TEFb phosphorylates RNA polymerase II and negative elongation factors to stimulate general transcriptional elongation. It is kept in a functional equilibrium through alternately interacting with its positive (the Brd4 protein) and negative (the HEXIM1 protein and 7SK snRNA) regulators. To investigate the physiological significance of this phenomenon, we analyzed the responses of HeLa cells and murine erythroleukemia cells (MELC) to hexamethylene bisacetamide (HMBA), which inhibits growth and induces differentiation of many cell types. For both cell types, an efficient, albeit temporary disruption of the 7SK-HEXIM1-P-TEFb snRNP and enhanced formation of the Brd4-P-TEFb complex occurred soon after the treatment started. When the P-TEFb-dependent HEXIM1 expression markedly increased as the treatment continued, the abundant HEXIM1 pushed the P-TEFb equilibrium back toward the 7SK/HEXIM1-bound state. For HeLa cells, as HMBA produced only a minor, temporary effect on their growth, the equilibrium gradually returned to its pretreatment level. In contrast, long-term treatment of MELC induced terminal division and differentiation. Concurrently, the P-TEFb equilibrium was shifted overwhelmingly toward the 7SK snRNP side. Together, these data link the P-TEFb equilibrium to the intracellular transcriptional demand and proliferative/differentiated states of cells.

Genomic organization of the translationally controlled tumor protein (TCTP) gene from shrimp Marsupenaeus japonicus.

The shrimp translationally controlled tumor protein (TCTP) gene was previously found up-regulated in response to viral infection. In order to further understand the transcriptional regulation of TCTP gene expression under viral challenge, the 5'-flanking promoter region of the TCTP gene in shrimp Marsupenaeus japonicus (Mj-TCTP) was cloned by using genomic walking method. The sequence shows that this region contains many important potential binding sites for transcription factors, such as activator protein1 (AP1), cAMP response element binding protein (CREB), Ets like transcription factor-1 (Elk-1), suggesting its expression is highly regulated. The promoter activity of this 5'-flanking region was confirmed by fusing to the enhanced green fluorescence protein (EGFP) gene and testing in Trichoplusia ni High Five cell line. Along with the introns and exons cloned in this study, the Mj-TCTP DNA sequence was reported here as the first TCTP gene with complete genomic organization in crustaceans.

ERRγ Promotes Angiogenesis, Mitochondrial Biogenesis, and Oxidative Remodeling in PGC1α/ß-Deficient Muscle.

PGC1α is a pleiotropic co-factor that affects angiogenesis, mitochondrial biogenesis, and oxidative muscle remodeling via its association with multiple transcription factors, including the master oxidative nuclear receptor ERRγ. To decipher their epistatic relationship, we explored ERRγ gain of function in muscle-specific PGC1α/ß double-knockout (PKO) mice. ERRγ-driven transcriptional reprogramming largely rescues muscle damage and improves muscle function in PKO mice, inducing mitochondrial biogenesis, antioxidant defense, angiogenesis, and a glycolytic-to-oxidative fiber-type transformation independent of PGC1α/ß. Furthermore, in combination with voluntary exercise, ERRγ gain of function largely restores mitochondrial energetic deficits in PKO muscle, resulting in a 5-fold increase in running performance. Thus, while PGC1s can interact with multiple transcription factors, these findings implicate ERRs as the major molecular target through which PGC1α/ß regulates both innate and adaptive energy metabolism.

NCoR1 restrains thymic negative selection by repressing Bim expression to spare thymocytes undergoing positive selection.

Thymocytes must pass both positive and negative selections to become mature T cells. Negative selection purges thymocytes whose T-cell receptors (TCR) exhibit high affinity to self-peptide MHC complexes (self pMHC) to avoid autoimmune diseases, while positive selection ensures the survival and maturation of thymocytes whose TCRs display intermediate affinity to self pMHCs for effective immunity, but whether transcriptional regulation helps conserve positively selected thymocytes from being purged by negative selection remains unclear. Here we show that the specific deletion of nuclear receptor co-repressor 1 (NCoR1) in T cells causes excessive negative selection to reduce mature thymocyte numbers. Mechanistically, NCoR1 protects positively selected thymocytes from negative selection by suppressing Bim expression. Our study demonstrates a critical function of NCoR1 in coordinated positive and negative selections in the thymus.Thymocytes are screened by two processes, termed positive and negative selections, which are permissive only for immature thymocytes with intermediate avidity to the selecting ligands. Here the authors show that the nuclear receptor NCoR1 suppresses Bim1 to inhibit negative selection and promote thymocyte survival.

Differential gene expression profile in hepatopancreas of WSSV-resistant shrimp (Penaeus japonicus) by suppression subtractive hybridization.

In order to find the immune-relevant factors responsible for the virus resistance in the WSSV-resistant shrimp, a suppression subtractive hybridization method was employed to identify differentially expressed genes and their expression profile in the hepatopancreas of the virus-resistant penaeid shrimp. Thirty five genes were identified from more than 400 clones, of which eight are found for the first time in penaeid shrimp. betaGBP is the most abundant gene in our subtractive library except hemocyanin. Lectin, ferritin, oxygenase and chitinase of the virus-resistant shrimp all showed up-regulation in expression compared with those of normal shrimp. In addition, Ranbp, Rho and Rab were found in the subtractive library. This is the first evidence indicating that small GTPases are involved in the signal transduction in shrimp defense response. Furthermore, a number of genes encoding apoptotic-related proteins and antioxidant enzymes were expressed at a higher level in the virus-resistant shrimp. In short, the high expression of immuno-related genes in response to the virus infection and the involvement of small GTPases in the antiviral response provide a new insight for further study in the crustacean innate immunity.

Differential profile of genes expressed in hemocytes of White Spot Syndrome Virus-resistant shrimp (Penaeus japonicus) by combining suppression subtractive hybridization and differential hybridization.

White Spot Syndrome Virus (WSSV) is the major viral pathogen of culture shrimp. Although remarkable progress has been made in characterizing the WSSV genome, information concerning the antiviral process of host is still limited. To identify the genes differentially expressed along with their expression profile in the hemocytes of the virus-resistant shrimp, suppression subtractive hybridization (SSH) and differential hybridization (DH) were employed. Relying on the sequences identified in the subtractive cDNA library, 30 genes were characterized to be involved in the antiviral process as defense-relevant, among them, 22 are found for the first time in penaeid shrimp. The most interesting finding is that the interferon-like protein (IntlP) and (2'-5') oligo(A) synthetase-like protein (data not shown) known as the antiviral factors showed increased expression in virus-resistant shrimp and the non-specific antiviral activity of IntlP protein was verified by cytotoxicity experiment. A number of proteins with certain similarities to the components of the complement and cytokines system in vertebrates were also found in the subtracted library. The high expression of redox-related factors (NADH dehydrogenase, glutathione peroxidase and transcription factor AP-1 precursor), plasma defensive protein (C-type lectin and laminin-like protein) and translationally controlled tumor protein (TCTP) in the virus-resistant shrimp suggested that they are essential components participating in the antiviral process. Our work provides a wide array of genes differentially expressed in the virus-resistant shrimp, and a framework for further studies aimed at antiviral mechanism in shrimp.

New insights into the control of HIV-1 transcription: when Tat meets the 7SK snRNP and super elongation complex (SEC).

Recent studies aimed at elucidating the mechanism controlling HIV-1 transcription have led to the identification and characterization of two multi-subunit complexes that both contain P-TEFb, a human transcription elongation factor and co-factor for activation of HIV-1 gene expression by the viral Tat protein. The first complex, termed the 7SK snRNP, acts as a reservoir where active P-TEFb can be withdrawn by Tat to stimulate HIV-1 transcription. The second complex, termed the super elongation complex (SEC), represents the form of P-TEFb delivered by Tat to the paused RNA polymerase II at the viral long terminal repeat during Tat transactivation. Besides P-TEFb, SEC also contains other elongation factors/co-activators, and they cooperatively stimulate HIV-1 transcription. Recent data also indicate SEC as a target for the mixed lineage leukemia (MLL) protein to promote the expression of MLL target genes and leukemogenesis. Given their roles in HIV-1/AIDS and cancer, further characterization of 7SK snRNP and SEC will help develop strategies to suppress aberrant transcriptional elongation caused by uncontrolled P-TEFb activation. As both complexes are also important for normal cellular gene expression, studying their structures and functions will elucidate the mechanisms that control metazoan transcriptional elongation in general.

Brd4 recruits P-TEFb to chromosomes at late mitosis to promote G1 gene expression and cell cycle progression.

Brd4, a bromodomain protein capable of interacting with acetylated histones, is implicated in transmitting epigenetic memory through mitosis. It also functions as an associated factor and positive regulator of P-TEFb, a Cdk9-cyclin T1 heterodimer that stimulates transcriptional elongation by phosphorylating RNA polymerase II. In the present study, experiments were performed to determine whether these two functions of Brd4 are interrelated and, if so, how they may impact cell cycle progression. Our data demonstrate that while the P-TEFb level remains constant, the Brd4-P-TEFb interaction increases dramatically in cells progressing from late mitosis to early G(1). Concurrently, P-TEFb is recruited to chromosomes, beginning around mid- to late anaphase and before nuclear envelope/lamina formation and nuclear import of other general transcription factors. Importantly, the recruitment of P-TEFb depends on Brd4. Abrogation of this process through Brd4 knockdown reduces the binding of P-TEFb to and expression of key G(1) and growth-associated genes, leading to G(1) cell cycle arrest and apoptosis. Because P-TEFb is synonymous with productive elongation, its recruitment by Brd4 to chromosomes at late mitosis may indicate those genes whose active transcription status must be preserved across cell division.

[Expression of a shrimp Kunitz-type protease inhibitor in Pichia pastoris and activity analysis].

SKPI (shrimp Kunitz-type protease inhibitor) from Marsupenaeus japonicus is a member of serine protease inhibitors which play an important role in the arthropod immunity. To fully understand its function in the innate immunity of shrimp, the skpi gene was cloned into a modified pPIC9K vector with a 6-His tag and expressed by Pichia pastoris GS115. The secretory SKPI was purified from the medium with high purity by using Ni Sepharose High Performance. This results also indicated that the purified SKPI could inhibit the activity of trypsin specifically.