Qi-Jing Li

The Transcriptional Repressor Bcl-6 Directs T Follicular Helper Cell Lineage Commitment

Follicular helper T (Tfh) cells provide selection signals to germinal center B cells, which is essential for long-lived antibody responses. High CXCR5 and low CCR7 expression facilitates their homing to B cell follicles and distinguishes them from T helper 1 (Th1), Th2, and Th17 cells. Here, we showed that Bcl-6 directs Tfh cell differentiation: Bcl-6-deficient T cells failed to develop into Tfh cells and could not sustain germinal center responses, whereas forced expression of Bcl-6 in CD4(+) T cells promoted expression of the hallmark Tfh cell molecules CXCR5, CXCR4, and PD-1. Bcl-6 bound to the promoters of the Th1 and Th17 cell transcriptional regulators T-bet and RORgammat and repressed IFN-gamma and IL-17 production. Bcl-6 also repressed expression of many microRNAs (miRNAs) predicted to control the Tfh cell signature, including miR-17-92, which repressed CXCR5 expression. Thus, Bcl-6 positively directs Tfh cell differentiation, through combined repression of miRNAs and transcription factors.

miR-19 is a key oncogenic component of mir-17-92

Recent studies have revealed the importance of multiple microRNAs (miRNAs) in promoting tumorigenesis, among which mir-17-92/Oncomir-1 exhibits potent oncogenic activity. Genomic amplification and elevated expression of mir-17-92 occur in several human B-cell lymphomas, and enforced mir-17-92 expression in mice cooperates with c-myc to promote the formation of B-cell lymphomas. Unlike classic protein-coding oncogenes, mir-17-92 has an unconventional gene structure, where one primary transcript yields six individual miRNAs. Here, we functionally dissected the individual components of mir-17-92 by assaying their tumorigenic potential in vivo. Using the Emu-myc model of mouse B-cell lymphoma, we identified miR-19 as the key oncogenic component of mir-17-92, both necessary and sufficient for promoting c-myc-induced lymphomagenesis by repressing apoptosis. The oncogenic activity of miR-19 is at least in part due to its repression of the tumor suppressor Pten. Consistently, miR-19 activates the Akt-mTOR (mammalian target of rapamycin) pathway, thereby functionally antagonizing Pten to promote cell survival. Our findings reveal the essential role of miR-19 in mediating the oncogenic activity of mir-17-92, and implicate the functional diversity of mir-17-92 components as the molecular basis for its pleiotropic effects during tumorigenesis.

Agonist/endogenous peptide|[ndash]|MHC heterodimers drive T cell activation and sensitivity

αβ T lymphocytes are able to detect even a single peptide–major histocompatibility complex (MHC) on the surface of an antigen-presenting cell. This is despite clear evidence, at least with CD4+ T cells, that monomeric ligands are not stimulatory. In an effort to understand how this remarkable sensitivity is achieved, we constructed soluble peptide–MHC heterodimers in which one peptide is an agonist and the other is one of the large number of endogenous peptide–MHCs displayed by presenting cells. We found that some specific combinations of these heterodimers can stimulate specific T cells in a CD4-dependent manner. This activation is severely impaired if the CD4-binding site on the agonist ligand is ablated, but the same mutation on an endogenous ligand has no effect. These data correlate well with analyses of lipid bilayers and cells presenting these ligands, and indicate that the basic unit of helper T cell activation is a heterodimer of agonist peptide– and endogenous peptide–MHC complexes, stabilized by CD4.

TGF-β-miR-34a-CCL22 Signaling-Induced Treg Cell Recruitment Promotes Venous Metastases of HBV-Positive Hepatocellular Carcinoma

Portal vein tumor thrombus (PVTT) is strongly correlated to a poor prognosis for patients with hepatocellular carcinoma (HCC). In this study, we uncovered a causative link between hepatitis B virus (HBV) infection and development of PVTT. Mechanistically, elevated TGF-β activity, associated with the persistent presence of HBV in the liver tissue, suppresses the expression of microRNA-34a, leading to enhanced production of chemokine CCL22, which recruits regulatory T (Treg) cells to facilitate immune escape. These findings strongly suggest that HBV infection and activity of the TGF-β-miR-34a-CCL22 axis serve as potent etiological factors to predispose HCC patients for the development of PVTT, possibly through the creation of an immune-subversive microenvironment to favor colonization of disseminated HCC cells in the portal venous system.

CD4 enhances T cell sensitivity to antigen by coordinating Lck accumulation at the immunological synapse

How T cells respond with extraordinary sensitivity to minute amounts of agonist peptide and major histocompatibility complex (pMHC) molecules on the surface of antigen-presenting cells bearing large numbers of endogenous pMHC molecules is not understood. Here we present evidence that CD4 affects the responsiveness of T helper cells by controlling spatial localization of the tyrosine kinase Lck in the synapse. This finding, as well as further in silico and in vitro experiments, led us to develop a molecular model in which endogenous and agonist pMHC molecules act cooperatively to amplify T cell receptor signaling. At the same time, activation due to endogenous pMHC molecules alone is inhibited. A key feature is that the binding of agonist pMHC molecules to the T cell receptor results in CD4-mediated spatial localization of Lck, which in turn enables endogenous pMHC molecules to trigger many T cell receptors. We also discuss broader implications for T cell biology, including thymic selection, diversity of the repertoire of self pMHC molecules and serial triggering.

miR-126 and miR-126 * repress recruitment of mesenchymal stem cells and inflammatory monocytes to inhibit breast cancer metastasis

The tumour stroma is an active participant during cancer progression. Stromal cells promote tumour progression and metastasis through multiple mechanisms including enhancing tumour invasiveness and angiogenesis, and suppressing immune surveillance. We report here that miR-126/miR-126*, a microRNA pair derived from a single precursor, independently suppress the sequential recruitment of mesenchymal stem cells and inflammatory monocytes into the tumour stroma to inhibit lung metastasis by breast tumour cells in a mouse xenograft model. miR-126/miR-126* directly inhibit stromal cell-derived factor-1 alpha (SDF-1α) expression, and indirectly suppress the expression of chemokine (C–C motif) ligand 2 (Ccl2) by cancer cells in an SDF-1α-dependent manner. miR-126/miR-126* expression is downregulated in cancer cells by promoter methylation of their host gene Egfl7. These findings determine how this microRNA pair alters the composition of the primary tumour microenvironment to favour breast cancer metastasis, and demonstrate a correlation between miR-126/126* downregulation and poor metastasis-free survival of breast cancer patients.

An endogenous positively selecting peptide enhances mature T cell responses and becomes an autoantigen in the absence of microRNA miR-181a.

Thymic positive selection is based on the interactions of T cell antigen receptors (TCRs) with self peptide–major histocompatibility complex (MHC) ligands, but the identity of selecting peptides for MHC class II–restricted TCRs and the functional consequences of this peptide specificity are not clear. Here we identify several endogenous self peptides that positively selected the MHC class II–restricted 5C.C7 TCR. The most potent of these also enhanced mature T cell activation, which supports the hypothesis that one function of positive selection is to produce T cells that can use particular self peptide–MHC complexes for activation and/or homeostasis. We also show that inhibiting the microRNA miR-181a resulted in maturation of T cells that overtly reacted toward these erstwhile positively selecting peptides. Therefore, miR-181a helps to guarantee the clonal deletion of particular moderate-affinity clones by modulating the TCR signaling threshold of thymocytes.

Molecular dissection of the miR-17-92 cluster's critical dual roles in promoting Th1 responses and preventing inducible Treg differentiation

Mir-17-92 encodes 6 miRNAs inside a single polycistronic transcript, the proper expression of which is critical for early B-cell development and lymphocyte homeostasis. However, during the T-cell antigen response, the physiologic function of endogenous miR-17-92 and the roles of the individual miRNAs remain elusive. In the present study, we functionally dissected the miR-17-92 cluster and revealed that miR-17 and miR-19b are the key players controlling Th1 responses through multiple coordinated biologic processes. These include: promoting proliferation, protecting cells from activation-induced cell death, supporting IFN-γ production, and suppressing inducible regulatory T-cell differentiation. Mechanistically, we identified Pten (phosphatase and tensin homolog) as the functionally important target of miR-19b, whereas the function of miR-17 is mediated by TGFβRII and the novel target CREB1. Because of its vigorous control over the Th1 cell-inducible regulatory T cell balance, the loss of miR-17-92 in CD4 T cells results in tumor evasion. Our results suggest that miR-19b and miR-17 could be harnessed to enhance the efficacy of T cell-based tumor therapy.

Facile synthesis of pentacle gold–copper alloy nanocrystals and their plasmonic and catalytic properties

The combination of gold and copper is a good way to pull down the cost of gold and ameliorate the instability of copper. Through shape control, the synergy of these two metals can be better exploited. Here, we report an aqueous phase route to the synthesis of pentacle gold–copper alloy nanocrystals with fivefold twinning, the size of which can be tuned in the range from 45 to 200 nm. The growth is found to start from a decahedral core, followed by protrusion of branches along twinning planes. Pentacle products display strong localized surface plasmon resonance peaks in the near-infrared region. Under irradiation by an 808-nm laser, 70-nm pentacle nanocrystals exhibit a notable photothermal effect to kill 4T1 murine breast tumours established on BALB/c mice. In addition, 70-nm pentacle nanocrystals show better catalytic activity than conventional citrate-coated 5-nm Au nanoparticles towards the reduction of p-nitrophenol to p-aminophenol by sodium borohydride.

Autophagy Regulates Endoplasmic Reticulum Homeostasis and Calcium Mobilization in T Lymphocytes

Macroautophagy (hereafter referred to as autophagy) is an evolutionarily conserved intracellular bulk degradation pathway that plays critical roles in eliminating intracellular pathogens, presenting endogenous Ags, and regulating T lymphocyte survival and proliferation. In this study, we have investigated the role of autophagy in regulating the endoplasmic reticulum (ER) compartment in T lymphocytes. We found that ER content is expanded in mature autophagy-related protein (Atg) 7-deficient T lymphocytes. Atg7-deficient T cells stimulated through the TCR display impaired influx, but not efflux, of calcium, and ER calcium stores are increased in Atg7-deficient T cells. Treatment with the ER sarco/ER Ca2+-ATPase pump inhibitor thapsigargin rescues the calcium influx defect in Atg7-deficient T lymphocytes, suggesting that this impairment is caused by an intrinsic defect in ER. Furthermore, we found that the stimulation-induced redistribution of stromal interaction molecule-1, a critical event for the store-operated Ca2+ release-activated Ca2+ channel opening, is impaired in Atg7-deficient T cells. Together, these findings indicate that the expanded ER compartment in Atg7-deficient T cells contains increased calcium stores, and the inability of these stores to be depleted causes defective calcium influx in these cells. Our results demonstrate that autophagy plays an important role in maintaining ER and calcium homeostasis in T lymphocytes.