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Dive into the research topics where Daniel L. Riggs is active.

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Featured researches published by Daniel L. Riggs.


The EMBO Journal | 2003

The Hsp90-binding peptidylprolyl isomerase FKBP52 potentiates glucocorticoid signaling in vivo

Daniel L. Riggs; Patricia J. Roberts; Samantha C. Chirillo; Joyce Cheung-Flynn; Viravan Prapapanich; Thomas Ratajczak; Richard F. Gaber; Didier Picard; David F. Smith

Hsp90 is required for the normal activity of steroid receptors, and in steroid receptor complexes it is typically bound to one of the immunophilin‐related co‐chaperones: the peptidylprolyl isomerases FKBP51, FKBP52 or CyP40, or the protein phosphatase PP5. The physiological roles of the immunophilins in regulating steroid receptor function have not been well defined, and so we examined in vivo the influences of immunophilins on hormone‐dependent gene activation in the Saccharomyces cerevisiae model for glucocorticoid receptor (GR) function. FKBP52 selectively potentiates hormone‐dependent reporter gene activation by as much as 20‐fold at limiting hormone concentrations, and this potentiation is readily blocked by co‐expression of the closely related FKBP51. The mechanism for potentiation is an increase in GR hormone‐binding affinity that requires both the Hsp90‐binding ability and the prolyl isomerase activity of FKBP52.


Molecular and Cellular Biology | 2007

Noncatalytic role of the FKBP52 peptidyl-prolyl isomerase domain in the regulation of steroid hormone signaling

Daniel L. Riggs; Marc B. Cox; Heather L. Tardif; Martin Hessling; Johannes Buchner; David F. Smith

ABSTRACT Hormone-dependent transactivation by several of the steroid hormone receptors is potentiated by the Hsp90-associated cochaperone FKBP52, although not by the closely related FKBP51. Here we analyze the mechanisms of potentiation and the functional differences between FKBP51 and FKBP52. While both have peptidyl-prolyl isomerase activity, this is not required for potentiation, as mutations abolishing isomerase activity did not affect potentiation. Genetic selection in Saccharomyces cerevisiae for gain of potentiation activity in a library of randomly mutated FKBP51 genes identified a single residue at position 119 in the N-terminal FK1 domain as being a critical difference between these two proteins. In both the yeast model and mammalian cells, the FKBP51 mutation L119P, which is located in a hairpin loop overhanging the catalytic pocket and introduces the proline found in FKBP52, conferred significant potentiation activity, whereas the converse P119L mutation in FKBP52 decreased potentiation. A second residue in this loop, A116, also influences potentiation levels; in fact, the FKBP51-A116V L119P double mutant potentiated hormone signaling as well as wild-type FKBP52 did. These results suggest that the FK1 domain, and in particular the loop overhanging the catalytic pocket, is critically involved in receptor interactions and receptor activity.


Critical Reviews in Biochemistry and Molecular Biology | 2004

Functional Specificity of Co-Chaperone Interactions with Hsp90 Client Proteins

Daniel L. Riggs; Marc B. Cox; Joyce Cheung-Flynn; Viravan Prapapanich; Patricia E. Carrigan; David F. Smith

A wide array of proteins in signal transduction pathways depend on Hsp90 and other chaperone components for functional maturation, regulation, and stability. Among these Hsp90 client proteins are steroid receptors, members from other classes of transcription factors, and representatives of both serine/threonine and tyrosine kinase families. Typically, dynamic complexes form on the client protein, and these consist of Hsp90- plus bound co-chaperones that often have enzymatic activities. In addition to its direct influence on client folding, Hsp90 locally concentrates co-chaperone activity within the client complex, and dynamic exchange of co-chaperones on Hsp90 facilitates sampling of co-chaperone activities that may, or may not, act on the client protein. We are just beginning to understand the nature of biochemical and molecular interactions between co-chaperone and Hsp90-bound client. This review focuses on the differential effects of Hsp90 co-chaperones toward client protein function and on the specificity that allows co-chaperones to discriminate between even closely related clients.


Leukemia | 2014

Promiscuous MYC locus rearrangements hijack enhancers but mostly super-enhancers to dysregulate MYC expression in multiple myeloma.

Maurizio Affer; Martha Chesi; W D Chen; Jonathan J. Keats; Y N Demchenko; K Tamizhmani; Victoria Garbitt; Daniel L. Riggs; Leslie A. Brents; A V Roschke; S. Van Wier; Rafael Fonseca; P L Bergsagel; W M Kuehl

MYC locus rearrangements—often complex combinations of translocations, insertions, deletions and inversions—in multiple myeloma (MM) were thought to be a late progression event, which often did not involve immunoglobulin genes. Yet, germinal center activation of MYC expression has been reported to cause progression to MM in an MGUS (monoclonal gammopathy of undetermined significance)-prone mouse strain. Although previously detected in 16% of MM, we find MYC rearrangements in nearly 50% of MM, including smoldering MM, and they are heterogeneous in some cases. Rearrangements reposition MYC near a limited number of genes associated with conventional enhancers, but mostly with super-enhancers (e.g., IGH, IGL, IGK, NSMCE2, TXNDC5, FAM46C, FOXO3, IGJ, PRDM1). MYC rearrangements are associated with a significant increase of MYC expression that is monoallelic, but MM tumors lacking a rearrangement have biallelic MYC expression at significantly higher levels than in MGUS. We also have shown that germinal center activation of MYC does not cause MM in a mouse strain that rarely develops spontaneous MGUS. It appears that increased MYC expression at the MGUS/MM transition usually is biallelic, but sometimes can be monoallelic if there is an MYC rearrangement. Our data suggest that MYC rearrangements, regardless of when they occur during MM pathogenesis, provide one event that contributes to tumor autonomy.


Proceedings of the National Academy of Sciences of the United States of America | 2011

Targeting the regulation of androgen receptor signaling by the heat shock protein 90 cochaperone FKBP52 in prostate cancer cells

Johanny Tonos De Leon; Aki Iwai; Clementine Feau; Yenni A. Garcia; Heather A. Balsiger; Cheryl L. Storer; Raquel Suro; Kristine M. Garza; Sunmin Lee; Yeong Sang Kim; Yu Chen; Yang Min Ning; Daniel L. Riggs; Robert J. Fletterick; R. Kiplin Guy; Jane B. Trepel; Leonard M. Neckers; Marc B. Cox

Drugs that target novel surfaces on the androgen receptor (AR) and/or novel AR regulatory mechanisms are promising alternatives for the treatment of castrate-resistant prostate cancer. The 52 kDa FK506 binding protein (FKBP52) is an important positive regulator of AR in cellular and whole animal models and represents an attractive target for the treatment of prostate cancer. We used a modified receptor-mediated reporter assay in yeast to screen a diversified natural compound library for inhibitors of FKBP52-enhanced AR function. The lead compound, termed MJC13, inhibits AR function by preventing hormone-dependent dissociation of the Hsp90-FKBP52-AR complex, which results in less hormone-bound receptor in the nucleus. Assays in early and late stage human prostate cancer cells demonstrated that MJC13 inhibits AR-dependent gene expression and androgen-stimulated prostate cancer cell proliferation.


Nature Medicine | 2016

IAP antagonists induce anti-tumor immunity in multiple myeloma

Marta Chesi; Noweeda Mirza; Victoria Garbitt; Meaghen E Sharik; Amylou C. Dueck; Yan W. Asmann; Ilseyar Akhmetzyanova; Heidi E. Kosiorek; Arianna Calcinotto; Daniel L. Riggs; Niamh Keane; Gregory J. Ahmann; Kevin M Morrison; Rafael Fonseca; Martha Q. Lacy; David Dingli; Shaji Kumar; Sikander Ailawadhi; Angela Dispenzieri; Francis Buadi; Morie A. Gertz; Craig B. Reeder; Yi Lin; Asher Chanan-Khan; A. Keith Stewart; David Fooksman; P. Leif Bergsagel

The cellular inhibitors of apoptosis (cIAP) 1 and 2 are amplified in about 3% of cancers and have been identified in multiple malignancies as being potential therapeutic targets as a result of their role in the evasion of apoptosis. Consequently, small-molecule IAP antagonists, such as LCL161, have entered clinical trials for their ability to induce tumor necrosis factor (TNF)-mediated apoptosis of cancer cells. However, cIAP1 and cIAP2 are recurrently homozygously deleted in multiple myeloma (MM), resulting in constitutive activation of the noncanonical nuclear factor (NF)-κB pathway. To our surprise, we observed robust in vivo anti-myeloma activity of LCL161 in a transgenic myeloma mouse model and in patients with relapsed-refractory MM, where the addition of cyclophosphamide resulted in a median progression-free-survival of 10 months. This effect was not a result of direct induction of tumor cell death, but rather of upregulation of tumor-cell-autonomous type I interferon (IFN) signaling and a strong inflammatory response that resulted in the activation of macrophages and dendritic cells, leading to phagocytosis of tumor cells. Treatment of a MM mouse model with LCL161 established long-term anti-tumor protection and induced regression in a fraction of the mice. Notably, combination of LCL161 with the immune-checkpoint inhibitor anti-PD1 was curative in all of the treated mice.


Cellular Signalling | 2011

The Pyk2 FERM regulates Pyk2 complex formation and phosphorylation.

Daniel L. Riggs; Zhongbo Yang; Jean Kloss; Joseph C. Loftus

The focal adhesion kinase Pyk2 integrates signals from cell adhesion receptors, growth factor receptors, and G-protein-coupled receptors leading to the activation of intracellular signaling pathways that regulate cellular phenotypes. The intrinsic mechanism for the activation of Pyk2 activity remains to be fully defined. Previously, we reported that mutations in the N-terminal FERM domain result in loss of Pyk2 activity and expression of the FERM domain as an autonomous fragment inhibits Pyk2 activity. In the present study, we sought to determine the mechanism that underlies these effects. Utilizing differentially epitope-tagged Pyk2 constructs, we observed that Pyk2 forms oligomeric complexes in cells and that complex formation correlates positively with tyrosine phosphorylation. Similarly, when expressed as an autonomous fragment, the Pyk2 FERM domain formed a complex with other Pyk2 FERM domains but not the FAK FERM domain. When co-expressed with full-length Pyk2, the autonomously expressed Pyk2 FERM domain formed a complex with full-length Pyk2 preventing the formation of Pyk2 oligomers and resulting in reduced Pyk2 phosphorylation. Deletion of the FERM domain from Pyk2 enhanced Pyk2 complex formation and phosphorylation. Together, these data indicate that the Pyk2 FERM domain is involved in the regulation of Pyk2 activity by acting to regulate the formation of Pyk2 oligomers that are critical for Pyk2 activity.


Journal of Signal Transduction | 2013

A Novel Interaction between Pyk2 and MAP4K4 Is Integrated with Glioma Cell Migration

Joseph C. Loftus; Zhongbo Yang; Jean Kloss; Harshil Dhruv; Nhan L. Tran; Daniel L. Riggs

Glioma cell migration correlates with Pyk2 activity, but the intrinsic mechanism that regulates the activity of Pyk2 is not fully understood. Previous studies have supported a role for the N-terminal FERM domain in the regulation of Pyk2 activity as mutations in the FERM domain inhibit Pyk2 phosphorylation. To search for novel protein-protein interactions mediated by the Pyk2 FERM domain, we utilized a yeast two-hybrid genetic selection to identify the mammalian Ste20 homolog MAP4K4 as a binding partner for the Pyk2 FERM domain. MAP4K4 coimmunoprecipitated with Pyk2 and was a substrate for Pyk2 but did not coimmunoprecipitate with the closely related focal adhesion kinase FAK. Knockdown of MAP4K4 expression inhibited glioma cell migration and effectively blocked Pyk2 stimulation of glioma cell. Increased expression of MAP4K4 stimulated glioma cell migration; however, this stimulation was blocked by knockdown of Pyk2 expression. These data support that the interaction of MAP4K4 and Pyk2 is integrated with glioma cell migration and suggest that inhibition of this interaction may represent a potential therapeutic strategy to limit glioblastoma tumor dispersion.


Cancer Research | 2014

Abstract 5489: Targeting MYC in multiple myeloma by BET protein inhibition

Daniel L. Riggs; Marta Chesi; P. Leif Bergsagel

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA The numerous and diverse genetic lesions in multiple myeloma (MM) make it difficult to discern those genetic abnormalities that may be suitable therapeutic targets. We have observed that the MYC locus is frequently rearranged in MM (about half of both patients and cell lines), suggesting that MYC dysregulation is a common feature of this disease. To evaluate MYC suppression as a therapeutic strategy in MM, we treated human myeloma cell lines with CPI203, a potent and selective inhibitor of bromodomain and extra-terminal (BET) proteins. The bromodomain inhibitor CPI203 has potency and selectivity similar to that of JQ1, but has improved pharmacokinetics for in vivo studies. From our collection of MM cell lines we have identified sensitive and resistant cell lines and characterized their response to CPI203 in detail. A number of conclusions have emerged from this work. First, response correlates with MYC protein levels after 3 days of treatment. MYC levels are significantly suppressed in sensitive lines and much less affected in resistant lines, supporting the hypothesis that MYC suppression alone determines cell fate in MM cell lines. In sensitive cell lines treatment with CPI203 caused a rapid (within 90 min.) decrease in MYC transcription that is consistent with the response being an intrinsic property of the cell lines. Inhibition of MYC transcription was followed by eventual cell cycle arrest and limited apoptosis in these sensitive cell lines. Both sensitive and resistant cell lines exhibited induction of Histone2H2BE gene in response to CPI203 treatment, indicating that drug efflux pumps alone do not mediate resistance. Surprisingly, several of the resistant cell lines exhibited an initial phase of sensitivity to BET inhibition. Upon drug addition, MYC transcription and MYC protein levels are repressed 2- to 5-fold, followed by a gradual recovery of MYC message and protein levels to the initial levels. In this second phase the cells are truly insensitive to BET inhibition: the drug remains active during this incubation and addition of fresh medium with drug does not affect MYC transcription. Furthermore, many aspects of the BET inhibition gene expression profile remain constant throughout this transition between sensitivity and resistance. These results suggest that the recovery phase is not a simple reversal of BET inhibition but rather the emergence of an alternative-signaling pathway that activates MYC expression in the presence of BET inhibition. Presently we are analyzing gene expression data to identify genes and signaling pathways responsible for this “induced resistance”. The identification of such pathways will help us better understand the molecular basis of the response to BET inhibition, which in turn might enable us to identify predictive biomarkers of the therapeutic response. Citation Format: Daniel L. Riggs, Marta Chesi, P Leif Bergsagel. Targeting MYC in multiple myeloma by BET protein inhibition. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5489. doi:10.1158/1538-7445.AM2014-5489


Molecular Endocrinology | 2005

Physiological Role for the Cochaperone FKBP52 in Androgen Receptor Signaling

Joyce Cheung-Flynn; Viravan Prapapanich; Marc B. Cox; Daniel L. Riggs; Carlos A. Suárez‐Quian; David F. Smith

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Marc B. Cox

University of Texas at El Paso

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Joyce Cheung-Flynn

Vanderbilt University Medical Center

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