Robert C Rickert

Sanford-Burnham Medical Research Institute, لا هویا, California, United States

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Publications (68)651.25 Total impact

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    ABSTRACT: Survivin is a member of the inhibitor of apoptosis family of proteins and a biomarker of poor prognosis in aggressive B cell non-Hodgkin's lymphoma. In addition to its role in inhibition of apoptosis, survivin also regulates mitosis. In this article, we show that deletion of survivin during early B cell development results in a complete block at the cycling pre-B stage. In the periphery, B cell homeostasis is not affected, but survivin-deficient B cells are unable to mount humoral responses. Correspondingly, we show that survivin is required for cell division in response to mitogenic stimulation. Thus, survivin is essential for proliferation of B cell progenitors and activated mature B cells, but is dispensable for B cell survival. Moreover, a small-molecule inhibitor of survivin strongly impaired the growth of representative B lymphoma lines in vitro, supporting the validity of survivin as an attractive therapeutic target for high-grade B cell non-Hodgkin's lymphoma.
    No preview · Article · Jan 2016 · The Journal of Immunology
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    ABSTRACT: Transient transfection of chemically synthesized microRNA (miRNA) mimics is being used extensively to study the functions and mechanisms of endogenous miRNAs. However, it remains unclear whether transfected miRNAs behave similarly to endogenous miRNAs. Here we show that transient transfection of miRNA mimics into HeLa cells by a commonly used method led to the accumulation of high molecular weight RNA species and a few hundred fold increase in mature miRNA levels. In contrast, expression of the same miRNAs through lentiviral infection or plasmid transfection of HeLa cells, transgenic expression in primary lymphocytes, and endogenous overexpression in lymphoma and leukemia cell lines did not lead to the appearance of high molecular weight RNA species. The increase of mature miRNA levels in these cells was below 10-fold, which was sufficient to suppress target gene expression and to drive lymphoma development in mice. Moreover, transient transfection of miRNA mimics at high concentrations caused non-specific alterations in gene expression, while at low concentrations achieved expression levels comparable to other methods but failed to efficiently suppress target gene expression. Small RNA deep sequencing analysis revealed that the guide strands of miRNA mimics were frequently mutated, while unnatural passenger strands of some miRNA mimics accumulated to high levels. The high molecular weight RNA species were a heterogeneous mixture of several classes of RNA species generated by concatemerization, 5'- and 3'-end tailing of miRNA mimics. We speculate that the supraphysiological levels of mature miRNAs and these artifactual RNA species led to non-specific changes in gene expression. Our results have important implications for the design and interpretation of experiments primarily employing transient transfection of miRNA mimics.
    Full-text · Article · Dec 2015 · Frontiers in Genetics
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    Robert Rickert

    Preview · Article · May 2015 · Journal of Experimental Medicine
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    ABSTRACT: BAFF, an activator of the noncanonical NFκB pathway, provides critical survival signals during B cell maturation and contributes to B cell proliferation. We found that the NFκB family member RelB is required ex vivo for B cell maturation, but cRel is required for proliferation. Combined molecular network modeling and experimentation revealed Nfkb2 p100 as a pathway switch; at moderate p100 synthesis rates in maturing B cells, BAFF fully utilizes p100 to generate the RelB:p52 dimer, whereas at high synthesis rates, p100 assembles into multimeric IκBsome complexes, which BAFF neutralizes in order to potentiate cRel activity and B cell expansion. Indeed, moderation of p100 expression or disruption of IκBsome assembly circumvented the BAFF requirement for full B cell expansion. Our studies emphasize the importance of p100 in determining distinct NFκB network states during B cell biology, which causes BAFF to have context-dependent functional consequences. Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.
    Full-text · Article · Dec 2014 · Cell Reports

  • No preview · Article · Oct 2014 · Cancer Research
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    ABSTRACT: Successful B cell differentiation and prevention of cell transformation depends on balanced and fine-tuned activation of cellular signaling pathways. The phosphatidyl inositol-3 kinase (PI3K) signaling pathway has emerged as a major regulator of B lymphocyte homeostasis and function. Phosphoinositide-dependent protein kinase-1 (PDK1) is the pivotal node in the PI3K pathway, regulating the stability and activity of downstream AGC kinases (including Akt, RSK, S6K, SGK, and PKC). Although the importance of PI3K activity in B cell differentiation is well documented, the role of PDK1 and other downstream effectors is underexplored. Here we used inducible and stage-specific gene targeting approaches to elucidate the role of PDK1 in early and peripheral B cell differentiation. PDK1 ablation enhanced cell cycle entry and apoptosis of IL-7-dependent pro-B cells, blocking Ig synthesis and B cell maturation. PDK1 also was essential for the survival and activation of peripheral B cells via regulation of PKC and Akt-dependent downstream effectors, such as GSK3α/β and Foxo1. We found that PDK1 deletion strongly impaired B cell receptor (BCR) signaling, but IL-4 costimulation was sufficient to restore BCR-induced proliferation. IL-4 also normalized PKCβ activation and hexokinase II expression in BCR-stimulated cells, suggesting that this signaling pathway can act independent of PDK1 to support B cell growth. In summary, our results demonstrate that PDK1 is indispensable for B cell survival, proliferation, and growth regulation.
    Full-text · Article · Jun 2014 · Proceedings of the National Academy of Sciences
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    ABSTRACT: Signaling through the BCR can drive B cell activation and contribute to B cell differentiation into Ab-secreting plasma cells. The positive BCR signal is counterbalanced by a number of membrane-localized inhibitory receptors that limit B cell activation and plasma cell differentiation. Deficiencies in these negative signaling pathways may cause autoantibody generation and autoimmune disease in both animal models and human patients. We have previously shown that the transcription factor Ets1 can restrain B cell differentiation into plasma cells. In this study, we tested the roles of the BCR and inhibitory receptors in controlling the expression of Ets1 in mouse B cells. We found that Ets1 is downregulated in B cells by BCR or TLR signaling through a pathway dependent on PI3K, Btk, IKK2, and JNK. Deficiencies in inhibitory pathways, such as a loss of the tyrosine kinase Lyn, the phosphatase Src homology region 2 domain-containing phosphatase 1 (SHP1) or membrane receptors CD22 and/or Siglec-G, result in enhanced BCR signaling and decreased Ets1 expression. Restoring Ets1 expression in Lyn- or SHP1-deficient B cells inhibits their enhanced plasma cell differentiation. Our findings indicate that downregulation of Ets1 occurs in response to B cell activation via either BCR or TLR signaling, thereby allowing B cell differentiation and that the maintenance of Ets1 expression is an important function of the inhibitory Lyn → CD22/SiglecG → SHP1 pathway in B cells.
    Full-text · Article · Jun 2014 · The Journal of Immunology
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    ABSTRACT: BAFF is a soluble factor required for B cell maturation and survival. BAFF-R signals via the noncanonical NF-κB pathway regulated by the TRAF3/NIK/IKK1 axis. We show that deletion of Ikk1 during early B cell development causes a partial impairment in B cell maturation and BAFF-dependent survival, but inactivation of Ikk1 in mature B cells does not affect survival. We further show that BAFF-R employs CD19 to promote survival via phosphatidylinositol 3-kinase (PI3K), and that coinactivation of Cd19 and Ikk1 causes a profound block in B cell maturation at the transitional stage. Consistent with a role for PI3K in BAFF-R function, inactivation of PTEN mediates a partial rescue of B cell maturation and function in Baff(-/-) animals. Elevated PI3K signaling also circumvents BAFF-dependent survival in a spontaneous B cell lymphoma model. These findings indicate that the combined activities of PI3K and IKK1 drive peripheral B cell differentiation and survival in a context-dependent manner.
    Full-text · Article · Nov 2013 · Cell Reports
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    ABSTRACT: Phosphoinositide-dependent kinase-1 (PDK1) is a serine/threonine protein kinase that phosphorylates members of the conserved AGC kinase superfamily, including AKT and protein kinase C (PKC), and is implicated in important cellular processes including survival, metabolism and tumorigenesis. In large cohorts of nevi and melanoma samples, PDK1 expression was significantly higher in primary melanoma, compared with nevi, and was further increased in metastatic melanoma. PDK1 expression suffices for its activity, owing to auto-activation, or elevated phosphorylation by phosphoinositide 3'-OH-kinase (PI3K). Selective inactivation of Pdk1 in the melanocytes of Braf(V600E)::Pten(-/-) or Braf(V600E)::Cdkn2a(-/-)::Pten(-/-) mice delayed the development of pigmented lesions and melanoma induced by systemic or local administration of 4-hydroxytamoxifen. Melanoma invasion and metastasis were significantly reduced or completely prevented by Pdk1 deletion. Administration of the PDK1 inhibitor GSK2334470 (PDKi) effectively delayed melanomagenesis and metastasis in Braf(V600E)::Pten(-/-) mice. Pdk1(-/-) melanomas exhibit a marked decrease in the activity of AKT, P70S6K and PKC. Notably, PDKi was as effective in inhibiting AGC kinases and colony forming efficiency of melanoma with Pten wild-type (WT) genotypes. Gene expression analyses identified Pdk1-dependent changes in FOXO3a-regulated genes, and inhibition of FOXO3a restored proliferation and colony formation of Pdk1(-/-) melanoma cells. Our studies provide direct genetic evidence for the importance of PDK1, in part through FOXO3a-dependent pathway, in melanoma development and progression.Oncogene advance online publication, 16 September 2013; doi:10.1038/onc.2013.383.
    Full-text · Article · Sep 2013 · Oncogene
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    ABSTRACT: The mammalian target of rapamycin (mTOR), an essential serine/threonine kinase, functions in biochemically distinct multi-protein complexes but little is known about roles of the complexes in B cells. The acutely rapamycin-sensitive mTOR complex 1 (mTORC1) is defined by a core subunit Raptor whereas mTORC2 lacks Raptor and instead has Rictor and SIN1 as distinct essential components. We now show that homeostasis and function of B cells require Rictor. Conditional deletion of Rictor prior to lymphoid specification impaired generation of mature follicular, marginal zone, and B1a B lymphocytes. Induced inactivation in adult mice caused cell-autonomous defects in B lymphoid homeostasis and antibody responses in vivo along with impacting plasma cells in bone marrow. Survival of B lymphocytes depended on Rictor, which was vital for normal induction of pro-survival genes, suppression of pro-apoptotic genes, NF-κB nuclear induction after BCR stimulation, and BAFF-induced NF-κB2/p52 generation. Collectively, the findings provide evidence that mTOR signaling impacts survival and proliferation of mature B lymphocytes, and establish Rictor as an important signal relay in B cell homeostasis, fate, and functions.
    Preview · Article · Aug 2013 · Blood
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    Robert C Rickert
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    ABSTRACT: The B cell receptor (BCR) and its precursor (pre-BCR) control B cell homeostasis, differentiation and function. Moreover, aberrant pre-BCR and BCR signalling have a central role in B cell neoplasia; for example, enhanced positive signalling or disrupted negative signalling downstream of the pre-BCR promotes B cell acute lymphocytic leukaemia. The emerging distinctions between tonic and chronic active BCR signalling have contributed to the identification of oncogenic targets downstream of BCR signalling in mature B cell neoplasms. Indeed, the encouraging results of several ongoing clinical trials that target the activity of phosphoinositide 3-kinase δ-isoform (PI3Kδ), Bruton tyrosine kinase (BTK) or spleen tyrosine kinase (SYK) downstream of the BCR highlight the therapeutic potential of inhibiting BCR signalling.
    Preview · Article · Aug 2013 · Nature Reviews Immunology
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    ABSTRACT: In the secondary lymphoid organs, intimate contact with follicular dendritic cells (FDCs) is required for B cell retention and Ag-driven selection during the germinal center response. However, selection of self-reactive B cells by Ag on FDCs has not been addressed. To this end, we generated a mouse model to conditionally express a membrane-bound self-antigen on FDCs and to monitor the fate of developing self-reactive B cells. In this article, we show that self-antigen displayed on FDCs mediates effective elimination of self-reactive B cells at the transitional stage. Notwithstanding, some self-reactive B cells persist beyond this checkpoint, showing evidence of Ag experience and intact proximal BCR signaling, but they are short-lived and unable to elicit T cell help. These results implicate FDCs as an important component of peripheral B cell tolerance that prevents the emergence of naive B cells capable of responding to sequestered self-antigens.
    Full-text · Article · Jul 2013 · The Journal of Immunology
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    ABSTRACT: The C1858T single nucleotide polymorphism in PTPN22, which is the gene encoding lymphoid tyrosine phosphatase (LYP), confers increased risk for various autoimmune disorders in Caucasians. Although the disease-associated LYP allele (LYP∗W620) is a gain-of-function variant that has higher catalytic activity than the major allele (LYP∗R620), it is still unclear how LYP∗W620 predisposes for autoimmunity. Here, we compared both T cell signaling and T cell function in healthy human donors homozygous for either LYP∗R620 or LYP∗W620. Generally, the presence of LYP∗W620 caused reduced proximal T cell antigen receptor-mediated signaling (e.g. ζ chain phosphorylation) but augmented CD28-associated signaling (e.g. AKT activation). Altered ligand binding properties of the two LYP variants could explain these findings since LYP∗R620 interacted more strongly with the p85 subunit of PI3K. Variation in signaling between cells expressing either LYP∗R620 or LYP∗W620 also affected the differentiation of conventional CD4(+) T cells. For example, LYP∗W620 homozygous donors displayed exaggerated Th1 responses (e.g. IFNγ production) and reduced Th17 responses (e.g. IL-17 production). Importantly, while regulatory T cells normally suppressed Th1-mediated IFNγ production in LYP∗R620 homozygous individuals, such suppression was lost in LYP∗W620 homozygous individuals. Altogether, these findings provide a molecular and cellular explanation for the autoimmune phenotype associated with LYP∗W620.
    Full-text · Article · Jan 2013 · Human immunology
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    ABSTRACT: Ubiquitously expressed D-type cyclins are required for hematopoiesis but are dispensable in other cell lineages. Furthermore, within different hematopoietic progenitor populations the D-type cyclins play nonredundant roles. The basis of this lineage and developmental specificity is unknown. In pro-B cells we demonstrate four distinct nuclear D-type cyclin compartments, including one cyclin D3 fraction associated with CDK4 and another phosphoinositide 3-kinase-regulated fraction not required for proliferation. A third fraction of cyclin D3 was associated with the nuclear matrix and repression of >200 genes including the variable (V) gene segments Igkv1-117, Iglv1, and Igh-VJ558. Consistent with different subnuclear compartments and functions, distinct domains of cyclin D3 mediated proliferation and Igk V gene segment repression. None of the cyclin D3 nuclear compartments overlapped with cyclin D2, which was distributed, unbound to CDK4, throughout the nucleus. Furthermore, compartmentalization of the cyclins appeared to be lineage restricted because in fibroblasts, cyclin D2 and cyclin D3 occupied a single nuclear compartment and neither bound CDK4 efficiently. These data suggest that subnuclear compartmentalization enables cyclin D3 to drive cell cycle progression and repress V gene accessibility, thereby ensuring coordination of proliferation with immunoglobulin recombination.
    Full-text · Article · Oct 2012 · Journal of Experimental Medicine
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    ABSTRACT: Ag receptor diversity involves the introduction of DNA double-stranded breaks during lymphocyte development. To ensure fidelity, cleavage is confined to the G(0)-G(1) phase of the cell cycle. One established mechanism of regulation is through periodic degradation of the RAG2 recombinase protein. However, there are additional levels of protection. In this paper, we show that cyclical changes in the IL-7R signaling pathway functionally segregate pro-B cells according to cell cycle status. In consequence, the level of a downstream effector of IL-7 signaling, phospho-STAT5, is inversely correlated with cell cycle expression of Rag, a key gene involved in recombination. Higher levels of phopho-STAT5 in S-G(2) correlate with decreased Rag expression and Rag relocalization to pericentromeric heterochromatin. These cyclical changes in transcription and locus repositioning are ablated upon transformation with v-Abl, which renders STAT5 constitutively active across the cell cycle. We propose that this activity of the IL-7R/STAT5 pathway plays a critical protective role in development, complementing regulation of RAG2 at the protein level, to ensure that recombination does not occur during replication. Our data, suggesting that pro-B cells are not a single homogeneous population, explain inconsistencies in the role of IL-7 signaling in regulating Igh recombination.
    Full-text · Article · May 2012 · The Journal of Immunology
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    Robert C Rickert · Guy S Salvesen · Carl F Ware
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    ABSTRACT: In a paper in this issue of the Biochemical Journal that questions the role of c-IAP1 (cellular inhibitor of apoptosis 1) in inflammation, new results from the Duckett laboratory remind us of the importance of truly knowing the mice we depend on. It turns out that c-IAP1 is tightly linked to caspase 11 and cannot be segregated by recombination. This disturbing result implies that immune functions ascribed to c-IAP1 may be due to the caspase 11 mutation that is co-inherited with the locus.
    Preview · Article · Apr 2012 · Biochemical Journal
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    Full-text · Dataset · Mar 2012
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    ABSTRACT: Lymphoid tyrosine phosphatase (LYP) and C-terminal Src kinase (CSK) are negative regulators of signaling mediated through the T-cell antigen receptor (TCR) and are thought to act in a cooperative manner when forming a complex. Here we studied the spatiotemporal dynamics of the LYP-CSK complex in T cells. We demonstrate that dissociation of this complex is necessary for recruitment of LYP to the plasma membrane, where it downmodulates TCR signaling. Development of a potent and selective chemical probe of LYP confirmed that LYP inhibits T-cell activation when removed from CSK. Our findings may explain the reduced TCR-mediated signaling associated with a single-nucleotide polymorphism that confers increased risk for certain autoimmune diseases, including type 1 diabetes and rheumatoid arthritis, and results in expression of a mutant LYP that is unable to bind CSK. Our compound also represents a starting point for the development of a LYP-based treatment of autoimmunity.
    Full-text · Article · Mar 2012 · Nature Chemical Biology
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    Robert C Rickert · Julia Jellusova · Ana V Miletic
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    ABSTRACT: Members of the tumor necrosis factor receptor superfamily (TNFRSF) participate prominently in B-cell maturation and function. In particular, B-cell activating factor belonging to the TNF family receptor (BAFF-R), B-cell maturation antigen (BCMA), and transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) play critical roles in promoting B-cell survival at distinct stages of development by engaging a proliferation-inducing ligand (APRIL) and/or BAFF. CD40 is also essential for directing the humoral response to T-cell-dependent antigens. Signaling by the TNFRSF is mediated primarily, albeit not exclusively, via the TNFR-associated factor (TRAF) proteins and activation of the canonical and/or non-canonical nuclear factor-κB (NF-κB) pathways. Dysregulated signaling by TNFRSF members can promote B-cell survival and proliferation, causing autoimmunity and neoplasia. In this review, we present a current understanding of the functions of and distinctions between APRIL/BAFF signaling by their respective receptors expressed on particular B-cell subsets. These findings are compared and contrasted with CD40 signaling, which employs similar signaling conduits to achieve distinct cellular outcomes in the context of the germinal center response. We also underscore how new findings and conceptual insights into TNFRSF signaling are facilitating the understanding of B-cell malignancies and autoimmune diseases.
    Preview · Article · Nov 2011 · Immunological Reviews
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    Matthew H Cato · Irene W Yau · Robert C Rickert
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    ABSTRACT: Detailed biochemical analysis of unmanipulated germinal center (GC) B cells has not been achieved. Previously, we designed and used a simple, economical and new magnetic bead separation scheme for the purification of 'untouched' mature GC and non-GC B cells from the spleens of immunized mice and reported the first biochemical assessment of the signaling cascades that contribute to cyclin D stability and GC B cell proliferation. Here we provide a detailed protocol for the method we used, which involves preparing single-cell suspension from the spleens of immunized mice, followed by labeling of nontarget cells with biotinylated antibodies specific for CD43, CD11c and IgD (for GC enrichment) or GL7 (for non-GC enrichment); these steps are followed by cell depletion using standard magnetic bead technology. This protocol can yield GC and non-GC B cells with purities exceeding 90%. The sorting process can be carried out in ∼1 h and provides a population of GC B cells of sufficient purity and quantity to allow ex vivo manipulation, including biochemical and genetic analysis as well as cell culture.
    Full-text · Article · Jun 2011 · Nature Protocol

Publication Stats

4k Citations
651.25 Total Impact Points

Institutions

  • 2005-2015
    • Sanford-Burnham Medical Research Institute
      • • Infectious and Inflammatory Disease Center
      • • Signal Transduction Research Program
      لا هویا, California, United States
  • 2010
    • The University of Manchester
      Manchester, England, United Kingdom
  • 1999-2004
    • University of California, San Diego
      • Department of Pharmacology
      San Diego, California, United States
  • 1995-1998
    • University of Cologne
      • Institute for Genetics
      Köln, North Rhine-Westphalia, Germany
  • 1990-1993
    • University of North Carolina at Chapel Hill
      • Department of Microbiology and Immunology
      North Carolina, United States