Person:
Roberts, Thomas

Profile Picture

Email Address

AA Acceptance Date

Birth Date

Research Projects

Organizational Units

Job Title

Last Name

Roberts

First Name

Thomas

Name

Roberts, Thomas

Filters

1993 - 199912010 - 20188

Settings

Author's Publications: search.filters.isAuthorOfPublication.17ba1508-ec2a-494e-ade2-d350ffc85f0a

Search Results

Now showing 1 - 9 of 9
  • No Thumbnail Available
    Publication
    Control of Cell Fate Determination by p21ras/Ras1, an Essential Component of Torso Signaling in Drosophila
    (Cold Spring Harbor Laboratory, 1993-04-01) Lu, Xiangyi; Chou, Tze-Bin; Williams, Nidhi Gupta; Roberts, Thomas; Perrimon, Norbert
    Determination of cell fate at the posterior termini of the Drosophila embryo is specified by the activation of the torso (tor) receptor tyrosine kinase. This signaling pathway is mediated by the serine/threonine kinase D-raf and a protein tyrosine phosphatase corkscrew (csw). We found that expression of an activated form of Ras1 during oogenesis resulted in embryos with tor gain-of-function phenotypes. To demonstrate that p21ras/Ras1 mediates tor signaling, we injected mammalian p21ras variants into early Drosophila embryos. We found that the injection of activated p21v-ras rescued the maternal-effect phenotypes of both tor and csw null mutations. These rescuing effects of p21v-ras are dependent on the presence of maternally derived D-raf activity. In addition, wild-type embryos show a terminal-class phenotype resembling csw when injected with p21rasN17, a dominant-negative form of p21ras. Furthermore, we have analyzed the maternal-effect phenotype of Son of sevenless (Sos), a positive regulator of Ras1, and showed that embryos derived from germ cells lacking Sos+ activity exhibit a terminal-class phenotype. Our study demonstrates that the Drosophila p21ras, encoded by Ras1, is an intrinsic component of the tor signaling pathway, where it is both necessary and sufficient in specifying posterior terminal cell fates. p21ras/Ras1 operates upstream of the D-raf kinase in this signaling pathway.
  • Thumbnail Image
    Publication
    Oridonin inhibits aberrant AKT activation in breast cancer
    (Impact Journals LLC, 2018) Sun, Bowen; Wang, Geng; Liu, Huidong; Liu, Pian; Twal, Waleed O.; Cheung, Hiuwing; Carroll, Steven L.; Ethier, Stephen P.; Mevers, Emily; Clardy, Jon; Roberts, Thomas; Chen, Changbin; Li, Qian; Wang, Lanfeng; Yang, Meixiang; Zhao, Jean; Wang, Qi
    Aberrant activation of phosphatidylinosito-4,5-bisphosphate 3-kinase/protein kinase B (PI3K/AKT) signaling in cancer has led to pursuit of inhibitors for targeting this pathway. However, inhibitors of PI3K and AKT have failed to yield efficacious results without adverse effects. Here, we screened a library containing 441 authenticated traditional chinese medicine (TCM) plant extracts by examining their effect on cell viability of a human mammary epithelial cell line HMEC-PIK3CAH1047R, which expresses mutant PIK3CAH1047R and has constitutively active AKT signaling. We found that Oridonin, an extract from Rabdosia rubescens, reduced cell viability to the greatest extent. Oridonin binds to AKT1 and potentially functions as an ATP-competitive AKT inhibitor. Importantly, Oridonin selectively impaired tumor growth of human breast cancer cells with hyperactivation of PI3K/AKT signaling. Moreover, Oridonin prevented the initiation of mouse mammary tumors driven by PIK3CAH1047R. Our results suggest that Oridonin may serve as a potent and durable therapeutic agent for the treatment of breast cancers with hyperactivation of PI3K/AKT signaling.
  • Thumbnail Image
    Publication
    Effective use of PI3K inhibitor BKM120 and PARP inhibitor Olaparib to treat PIK3CA mutant ovarian cancer
    (Impact Journals LLC, 2016) Wang, Dong; Wang, Min; Jiang, Nan; Zhang, Yuan; Bian, Xing; Wang, Xiaoqing; Roberts, Thomas; Zhao, Jean; Liu, Pixu; Cheng, Hailing
    Recent preclinical studies revealed the efficacy of combined use of PI3K inhibitor BKM120 and PARP inhibitor Olaparib in breast and prostate cancers. The current study investigated the effect of such drug combination on ovarian cancer. Here we showed that combined inhibition of PI3K and PARP effectively synergized to inhibit proliferation, survival and invasion in the majority of ovarian cancer cell lines harboring PIK3CA mutations, including SKOV3, HEYA8, and IGROV1. Mechanistically, combined treatment of PARP and PI3K inhibitors resulted in an exacerbated DNA damage response and more substantially reduced AKT/mTOR signaling when compared to single-agent. Notably, ovarian cancer cells responsive to the PI3K/PARP combination displayed decreased BRCA1/2 expression upon drug treatment. Furthermore, the effect of the drug combination was corroborated in an intraperitoneal dissemination xenograft mouse model in which SKOV3 ovarian cancer cells responded with significantly decreased BRCA1 expression, suppressed PI3K/AKT signaling and reduced tumor burden. Collectively, our data suggested that combined inhibition of PI3K and PARP may be an effective therapeutic strategy for ovarian cancers with PIK3CA mutations and that the accompanied BRCA downregulation following PI3K inhibition could serve as a biomarker for the effective response to PARP inhibition.
  • Thumbnail Image
    Publication
    Rac1-mediated membrane raft localization of PI3K/p110β is required for its activation by GPCRs or PTEN loss
    (eLife Sciences Publications, Ltd, 2016) Cizmecioglu, Onur; Ni, Jing; Xie, Shaozhen; Zhao, Jean; Roberts, Thomas
    We aimed to understand how spatial compartmentalization in the plasma membrane might contribute to the functions of the ubiquitous class IA phosphoinositide 3-kinase (PI3K) isoforms, p110α and p110β. We found that p110β localizes to membrane rafts in a Rac1-dependent manner. This localization potentiates Akt activation by G-protein-coupled receptors (GPCRs). Thus genetic targeting of a Rac1 binding-deficient allele of p110β to rafts alleviated the requirement for p110β-Rac1 association for GPCR signaling, cell growth and migration. In contrast, p110α, which does not play a physiological role in GPCR signaling, is found to reside in nonraft regions of the plasma membrane. Raft targeting of p110α allowed its EGFR-mediated activation by GPCRs. Notably, p110β dependent, PTEN null tumor cells critically rely upon raft-associated PI3K activity. Collectively, our findings provide a mechanistic account of how membrane raft localization regulates differential activation of distinct PI3K isoforms and offer insight into why PTEN-deficient cancers depend on p110β. DOI: http://dx.doi.org/10.7554/eLife.17635.001
  • Thumbnail Image
    Publication
    Combination inhibition of PI3K and mTORC1 yields durable remissions in orthotopic patient-derived xenografts of HER2-positive breast cancer brain metastases
    (2016) Ni, Jing; Ramkissoon, Shakti H.; Xie, Shaozhen; Goel, Shom; Stover, Daniel G.; Guo, Hanbing; Luu, Victor; Marco, Eugenio; Ramkissoon, Lori A.; Kang, Yun Jee; Hayashi, Marika; Nguyen, Quang-De; Ligon, Azra; Du, Rose; Claus, Elizabeth; Alexander, Brian; Yuan, Guo-Cheng; Wang, Zhigang C.; Iglehart, J. Dirk; Krop, Ian; Roberts, Thomas; Winer, Eric; Lin, Nancy; Ligon, Keith; Zhao, Jean
    Brain metastases represent the greatest clinical challenge in treating HER2-positive breast cancer. We report the development of orthotopic patient-derived xenografts (PDXs) of HER2-expressing breast cancer brain metastases (BCBM), and their use for the identification of targeted combination therapies. Combined inhibition of PI3K and mTOR resulted in durable tumor regressions in three of five PDXs, and therapeutic response correlated with reduction of 4EBP1 phosphorylation. The two non-responding PDXs showed hypermutated genomes with enrichment of mutations in DNA repair genes, suggesting an association of genomic instability with therapeutic resistance. These findings suggest that a biomarker-driven clinical trial of PI3K inhibitor plus an mTOR inhibitor should be conducted for patients with HER2-positive BCBM.
  • Thumbnail Image
    Publication
    Polyoma small T antigen triggers cell death via mitotic catastrophe
    (2014) Fernando, Arun T Pores; Andrabi, Shaida; Cizmecioglu, Onur; Zhu, Cailei; Livingston, David M.; Higgins, Jonathan M.G; Schaffhausen, Brian S; Roberts, Thomas
    Polyoma small T antigen (PyST), an early gene product of the polyoma virus, has been shown to cause cell death in a number of mammalian cells in a protein phosphatase 2A (PP2A)-dependent manner. In the current study, using a cell line featuring regulated expression of PyST, we found that PyST arrests cells in mitosis. Live-cell and immunofluorescence studies showed that the majority of the PyST-expressing cells were arrested in prometaphase with almost no cells progressing beyond metaphase. These cells exhibited defects in chromosomal congression, sister chromatid cohesion and spindle positioning, resulting in the activation of the Spindle Assembly Checkpoint (SAC). Prolonged mitotic arrest then led to cell death via mitotic catastrophe. Cell cycle inhibitors that block cells in G1/S prevented PyST-induced death. PyST-induced cell death that occurs during M is not dependent on p53 status. These data suggested, and our results confirmed that, PP2A inhibition could be used to preferentially kill cancer cells with p53 mutations that proliferate normally in the presence of cell cycle inhibitors.
  • Thumbnail Image
    Publication
    A PI3K p110β–Rac signalling loop mediates Pten-loss-induced perturbation of haematopoiesis and leukaemogenesis
    (Nature Pub. Group, 2015) Yuzugullu, Haluk; Baitsch, Lukas; Von, Thanh; Steiner, Allison; Tong, Haoxuan; Ni, Jing; Clayton, Linda K.; Bronson, Roderick; Roberts, Thomas; Gritsman, Kira; Zhao, Jean
    The tumour suppressor PTEN, which antagonizes PI3K signalling, is frequently inactivated in haematologic malignancies. In mice, deletion of PTEN in haematopoietic stem cells (HSCs) causes perturbed haematopoiesis, myeloproliferative neoplasia (MPN) and leukaemia. Although the roles of the PI3K isoforms have been studied in PTEN-deficient tumours, their individual roles in PTEN-deficient HSCs are unknown. Here we show that when we delete PTEN in HSCs using the Mx1–Cre system, p110β ablation prevents MPN, improves HSC function and suppresses leukaemia initiation. Pharmacologic inhibition of p110β in PTEN-deficient mice recapitulates these genetic findings, but suggests involvement of both Akt-dependent and -independent pathways. Further investigation reveals that a p110β–Rac signalling loop plays a critical role in PTEN-deficient HSCs. Together, these data suggest that myeloid neoplasia driven by PTEN loss is dependent on p110β via p110β–Rac-positive-feedback loop, and that disruption of this loop may offer a new and effective therapeutic strategy for PTEN-deficient leukaemia.
  • Thumbnail Image
    Publication
    NTRK2 activation cooperates with PTEN deficiency in T-ALL through activation of both the PI3K–AKT and JAK–STAT3 pathways
    (Nature Publishing Group, 2016) Yuzugullu, Haluk; Von, Thanh; Thorpe, Lauren M; Walker, Sarah; Roberts, Thomas; Frank, David; Zhao, Jean
    Loss of PTEN, a negative regulator of the phosphoinositide 3-kinase signaling pathway, is a frequent event in T-cell acute lymphoblastic leukemia, suggesting the importance of phosphoinositide 3-kinase activity in this disease. Indeed, hyperactivation of the phosphoinositide 3-kinase pathway is associated with the disease aggressiveness, poor prognosis and resistance to current therapies. To identify a molecular pathway capable of cooperating with PTEN deficiency to drive oncogenic transformation of leukocytes, we performed an unbiased transformation screen with a library of tyrosine kinases. We found that activation of NTRK2 is able to confer a full growth phenotype of Ba/F3 cells in an IL3-independent manner in the PTEN-null setting. NTRK2 activation cooperates with PTEN deficiency through engaging both phosphoinositide3-kinase/AKT and JAK/STAT3 pathway activation in leukocytes. Notably, pharmacological inhibition demonstrated that p110α and p110δ are the major isoforms mediating the phosphoinositide 3-kinase/AKT signaling driven by NTRK2 activation in PTEN-deficient leukemia cells. Furthermore, combined inhibition of phosphoinositide 3-kinase and STAT3 significantly suppressed proliferation of PTEN-mutant T-cell acute lymphoblastic leukemia both in culture and in mouse xenografts. Together, our data suggest that a unique conjunction of PTEN deficiency and NTRK2 activation in T-cell acute lymphoblastic leukemia, and combined pharmacologic inhibition of phosphoinositide 3-kinase and STAT3 signaling may serve as an effective and durable therapeutic strategy for T-cell acute lymphoblastic leukemia.
  • Thumbnail Image
    Publication
    Medulloblastoma Exome Sequencing Uncovers Subtype-Specific Somatic Mutations
    (2012) Pugh, Trevor J.; Weeraratne, Shyamal Dilhan; Archer, Tenley; Pomeranz Krummel, Daniel A.; Auclair, Daniel; Bochicchio, James; Carneiro, Mauricio O.; Carter, Scott L.; Cibulskis, Kristian; Erlich, R; Greulich, Heidi; Lawrence, Michael; Lennon, Niall; McKenna, Aaron; Meldrim, James; Ramos, Alex H.; Ross, Michael G.; Russ, Carsten; Shefler, Erica; Sivachenko, Andrey; Sogoloff, Brian; Stojanov, Petar; Tamayo, Pablo; Mesirov, Jill; Amani, Vladimir; Teider, Natalia; Sengupta, Soma; Francois, Jessica Pierre; Northcott, Paul A.; Taylor, Michael D.; Yu, Furong; Crabtree, Gerald R.; Kautzman, Amanda G.; Gabriel, Stacey B.; Getz, Gad; Jäger, Natalie; Jones, David T. W.; Lichter, Peter; Pfister, Stefan M.; Roberts, Thomas; Meyerson, Matthew; Pomeroy, Scott; Cho, Yoon-Jae
    Medulloblastomas are the most common malignant brain tumors in children1. Identifying and understanding the genetic events that drive these tumors is critical for the development of more effective diagnostic, prognostic and therapeutic strategies. Recently, our group and others described distinct molecular subtypes of medulloblastoma based on transcriptional and copy number profiles2–5. Here, we utilized whole exome hybrid capture and deep sequencing to identify somatic mutations across the coding regions of 92 primary medulloblastoma/normal pairs. Overall, medulloblastomas exhibit low mutation rates consistent with other pediatric tumors, with a median of 0.35 non-silent mutations per megabase. We identified twelve genes mutated at statistically significant frequencies, including previously known mutated genes in medulloblastoma such as CTNNB1, PTCH1, MLL2, SMARCA4 and TP53. Recurrent somatic mutations were identified in an RNA helicase gene, DDX3X, often concurrent with CTNNB1 mutations, and in the nuclear co-repressor (N-CoR) complex genes GPS2, BCOR, and LDB1, novel findings in medulloblastoma. We show that mutant DDX3X potentiates transactivation of a TCF promoter and enhances cell viability in combination with mutant but not wild type beta-catenin. Together, our study reveals the alteration of Wnt, Hedgehog, histone methyltransferase and now N-CoR pathways across medulloblastomas and within specific subtypes of this disease, and nominates the RNA helicase DDX3X as a component of pathogenic beta-catenin signaling in medulloblastoma.