Suppressive mechanisms operating within T cells are linked to immune dysfunction in the tumor microenvironment. We have previously reported using adoptive T cell immunotherapy models that tumor–bearing mice treated with a regimen of proteasome inhibitor, bortezomib - a dipeptidyl boronate, show increased antitumor lymphocyte effector function and survival. Here, we identify a mechanism for the improved antitumor CD8+ T cell function following bortezomib treatment. Intravenous administration of bortezomib at a low dose (1 mg/kg body weight) in wild-type or tumor-bearing mice altered the expression of a number of miRNAs in CD8+ T cells. Specifically, the effect of bortezomib was prominent on miR-155 - a key cellular miRNA involved in T cell function. Importantly, bortezomib–induced upregulation of miR-155 was associated with the downregulation of its targets, the suppressor of cytokine signaling 1 (SOCS1) and inositol polyphosphate-5-phosphatase (SHIP1). Genetic and biochemical analysis confirmed a functional link between miR-155 and these targets. Moreover, activated CD8+ T cells treated with bortezomib exhibited a significant reduction in programmed cell death-1 (PD-1) expressing SHIP1+ phenotype. These data underscore a mechanism of action by which bortezomib induces miR-155–dependent downregulation of SOCS1 and SHIP1 negative regulatory proteins, leading to a suppressed PD-1–mediated T cell exhaustion. Collectively, data provide novel molecular insights into bortezomib–mediated lymphocyte–stimulatory effects that could overcome immunosuppressive actions of tumor on antitumor T cell functions. The findings support the approach that bortezomib combined with other immunotherapies would lead to improved therapeutic outcomes by overcoming T cell exhaustion in the tumor microenvironment.

Cleavage and polyadenylation specificity factor 6 (CPSF6) is a cellular protein involved in mRNA processing. Emerging evidence suggests that CPSF6 also plays key roles in HIV-1 infection, specifically during nuclear import and integration targeting. However, the cellular and molecular mechanisms that regulate CPSF6 expression are largely unknown. In this study, we report a post-transcriptional mechanism that regulates CPSF6 via the cellular microRNA miR-125b. An in silico analysis revealed that the 3′UTR of CPSF6 contains a miR-125b–binding site that is conserved across several mammalian species. Because miRNAs repress protein expression, we tested the effects of miR-125b expression on CPSF6 levels in miR-125b knockdown and over-expression experiments, revealing that miR-125b and CPSF6 levels are inversely correlated. To determine whether miR-125b post-transcriptionally regulates CPSF6, we introduced the 3′UTR of CPSF6 mRNA into a luciferase reporter and found that miR-125b negatively regulates CPSF6 3′UTR-driven luciferase activity. Accordingly, mutations in the miR-125b seed sequence abrogated the regulatory effect of the miRNA on the CPSF6 3′UTR. Finally, pulldown experiments demonstrated that miR-125b physically interacts with CPSF6 3′UTR. Interestingly, HIV-1 infection down-regulated miR-125b expression concurrent with up-regulation of CPSF6. Notably, miR-125b down-regulation in infected cells was not due to reduced pri-miRNA or pre-miRNA levels. However, miR-125b down-regulation depended on HIV-1 reverse transcription but not viral DNA integration. These findings establish a post-transcriptional mechanism that controls CPSF6 expression and highlight a novel function of miR-125b during HIV-host interaction.

The cleavage and polyadenylation specificity factor 6 (CPSF6) is a cellular protein involved in RNA cleavage and polyadenylation. Emerging evidence also suggest that CPSF6 plays a key role during HIV‐1 infection by guiding integration of the viral DNA into gene‐dense regions of the host genome. Since viral DNA integration is a critical step of HIV‐1 infection, the role of CPSF6 in the virus lifecycle is being intensely investigated. Surprisingly, the cellular mechanisms that regulate CPSF6 expression are largely unknown. In this study, we report a post‐transcriptional mechanism of regulation of CPSF6. Our initial bioinformatics analysis revealed that the 3′ untranslated region (3′UTR) of Cpsf6 contains a binding site for the cellular miRNA miR‐125b that is strikingly conserved across different mammalian species. Since miRNAs negatively regulate protein expression, we carried out knock‐down and over‐expression studies of miR‐125b. Results from these experiments revealed that miR‐125b expression is negatively associated with CPSF6 protein levels. Interestingly, HIV‐1 infection resulted in the down‐regulation of miR‐125b concurrent with induction of CPSF6. To probe that CPSF6 expression is post‐transcriptionally regulated by miR‐125b, we cloned the 3′UTR regions of Cpsf6 mRNA into a luciferase reporter. Results from luciferase assay provide evidence that miR‐125b expression negatively regulates Cpsf6 3′UTR activity. Accordingly, mutations in the miR‐125b seed sequences abrogated the regulatory effect of the miRNA on Cpsf6 3′UTR. Pull‐down studies demonstrated that miR‐125b physically interacts with the Cpsf6 mRNA. Continuing studies probe the necessity of productive HIV‐1 infection for negatively regulating miR‐125b expression as well as to elucidate the pathway through which HIV‐1 infection can knockdown miR‐125b expression. Collectively, these findings establish a post‐transcriptional mechanism of CPSF6 expression and describe a novel function of miR‐125b in virus‐host interaction. Support or Funding Information This work is partly supported by grants DA024558, DA30896, DA033892 and DA021471 from NIDA/NIH to CD. We also acknowledge the RCMI Grant G12MD007586, the Vanderbilt CTSA grant UL1RR024975, the Meharry Translational Research Center (MeTRC) CTSA grant (U54 RR026140 from NCRR/NIH, the U54 grant MD007593 from NIMHD/NIH, and Tennessee CFAR grant (P30 AI110527).

The immunosuppressive tumor microenvironment dampens host antitumor immunity by multiple mechanisms including interfering with various cell signaling pathways that aid in the differentiation and function of immune cells. We have taken an immunotherapeutic approach in order to strengthen antitumor immunity in mice bearing solid tumors, specifically breast tumors. In doing so, we observed that treatment with bortezomib, an FDA-approved proteasome inhibitor, has the ability to increase CD8+T lymphocyte IFNγ secretion and expression of effector molecules, perforin, granzyme-B and the T-box transcription factor eomesodermin. In order to understand the molecular mechanism(s) of how bortezomib works to improve antitumor immunity we sought to explore its effects on miRNA expression as well as function. We found that treatment of wild-type or tumor-bearing BALB/c mice with bortezomib modulated the expression of various miRNAs in CD8+T cells. From miRNA array data, we identified miR-155 as one prominent modulator of antitumor CD8+T cell immune functions. miR-155 has been accredited to controlling CD8+T cell responses by regulating interferon signaling in viral infections and cancer. We are currently elucidating the mechanisms of bortezomib-mediated effects on miR-155 and its targets, such as suppressor of cytokine signaling 1 (SOCS1) and inositol polyphosphate-5-phosphatase (SHIP1) that are associated with T cell function. These data provide novel insights on using bortezomib not only as an agent to sensitize tumors to cell death, but also to provide lymphocyte-stimulatory effects that could overcome immunosuppressive actions of tumor on antitumor T cell function.

Nanoparticle‐based delivery systems represent a new paradigm for drug design. Many pathogenic diseases, such as leishmaniasis, can be efficiently treated by localized, macrophage‐targeted therapies. The parasitic protozoan Leishmania invades mammalian macrophages to establish infection. We reported previously that Leishmania manipulates the expression of several non‐coding RNA genes (e.g., Alu RNA, B1 RNA and SRP RNA) in the macrophages to favor the establishment of their infection in the phagolysosomes of these cells (Ueda Y., and Chaudhuri, G. J. Biol. Chem. 275, 19428, 2000; Misra, S., Tripathi, M. K., and Chaudhuri, G. J. Biol. Chem. 280, 29364, 2005). Our recent data suggests that Leishmania exposure to the macrophages leads to the decrease in several ncRNA levels including various miRNAs. Replenishment of these RNAs in macrophages can make them relatively resistant to Leishmania infection. Here we report the use of hollow yeast cell wall particles (YCWPs) caging the above ncRNAs for delivery to macrophages in order to make them resistant to Leishmania infection. Our findings support the idea that YCWPs mediated delivery to macrophages can beused to replenish RNA or knock down specific genes within these cells to exert therapeutic effects against Leishmaniasis. Supported by NIH NIAID grants R01AI042327 and R21AI076757 to GC.