May 22, 20176:30 PMPhD Graduate ReceptionMarina del Rey
May 23, 20173:00 PMCommencementDavid Geffen Hall
Tuesday, May 02, 201712:00 PM
Thesis Defense Seminar: "HGF mediates breast tumor cell migration towards blood vessels."Edison Leung
Monday, March 20, 2017
Longyue (Lily) Cao
“Control of mitochondrial function and cell growth by the atypical cadherin Fat1”
Mentor: Dr. Nicholas Sibinga, Department of Developmental and Molecular Biology
After vascular injury, smooth muscle cells (SMCs) proliferate, migrate, and downregulate contractile protein expression. Proper control of cell growth during this process prevents SMC overproliferation within the vasculature and the development of occlusive cardiovascular diseases like atherosclerosis. The atypical cadherin Fat1, upregulated in SMCs after vascular injury and in response to growth stimulation in vitro, limits SMC growth. We found that Fat1 intracellular domain (ICD) species accumulate in SMC mitochondria and associate with respiratory proteins critical for energy metabolism. Therefore, we hypothesized that Fat1 regulates mitochondrial function to control SMC growth. Loss of Fat1 (Fat1KO) in cultured SMCs increased the rate of cell growth. In addition, Fat1KO cells had higher baseline and maximal mitochondrial oxygen consumption rates (OCRs), as well as ATP and aspartate production. Suppressing mitochondrial respiration eliminated the growth advantage of Fat1KO cells, suggesting that Fat1 modulates SMC growth by restricting mitochondrial function. Mitochondrial-specific Fat1ICD rescued the elevated OCRs in Fat1KO cells. Furthermore, Fat1ICD species associated with and repressed complexes I and II activities. BN-PAGE analysis of intact mitochondrial complexes showed that Fat1ICD species co-migrate with respiratory supercomplexes and oppose complex I incorporation into these higher-order structures. In vivo, vessels from SMC-specific Fat1 knockout mice (Fat1SMKO) exhibited increased medial hyperplasia and neointimal growth after injury, with increased SMC proliferation and superoxide production. SMCs isolated from injured Fat1SMKO vessels had higher OCRs than those from injured control vessels. In sum, Fat1 prevents an exaggerated SMC growth response after vascular injury by repressing the intrinsic activities of mitochondrial respiratory complexes and their incorporation into supercomplexes.
“Central nervous system Chrm1 signals prime hematopoietic stem cells for mobilization via a glucocorticoid mediated relay”
Mentor: Dr. Paul Frenette, Department of Cell Biology
Mobilization of hematopoietic stem cells (HSCs) from the bone marrow (BM) into blood can be elicited by the cytokine granulocyte-colony stimulating factor (G-CSF). The mechanism by which G-CSF-elicited mobilization occurs is a complex process who’s many cellular and molecular targets may not be fully elucidated as of yet. In this study, we identify that muscarinic receptor type-1 (Chrm1) signaling within the central nervous system (CNS) promotes G-CSF mobilization of HSCs. Parabiosis of Chrm1-/- mice with wild-type (WT) mice was sufficient to rescue Chrm1-/- impaired HSC mobilization, suggesting a blood borne factor mediates the relay of central signals. Our studies identified Chrm1-/- mice to have reductions in glucocorticoids (GCs), leading us to explore its role in HSC mobilization. Exogenous administration of GCs to Chrm1-/- mice was sufficient to restore HSC mobilization to WT levels; conversely, inhibition of GCs production in WT animals reduced HSC mobilization. Mice harboring a GC receptor (Nr3c1) deficient hematopoietic system also exhibited reductions in HSC mobilization. Chrm1, was able to activate the hypothalamic-pituitary-adrenal axis by stimulating production of corticotropoin releasing hormone. Further studies found that hematopoietic cells isolated from Chrm1-/- and Nr3c1Δ/Δ mice exhibited reduced polymerized actin compared to WT cells and were restored by administration of GCs to Chrm1-/- mice. This suggests that steady state levels of GCs in the BM prime HSCs for G-CSF elicited mobilization uncovering a novel long-range regulation of HSC migration.
“A myeloid tumor suppressor role for NOL3”
Mentor: Dr. Ulrich Steidl, Department of Cell Biology
Despite the identification of several oncogenic driver mutations leading to constitutive JAK-STAT activation, the cellular and molecular biology of myeloproliferative neoplasms (MPN) remains incompletely understood. Recent discoveries have identified underlying disease-modifying molecular aberrations contributing to disease initiation and progression. Here, we report that deletion of Nol3 (Nucleolar protein 3) in mice leads to an MPN resembling primary myelofibrosis (PMF). Nol3-/- MPN mice harbor an expanded Thy1+LSK stem cell population exhibiting increased cell cycling and a myelomonocytic differentiation bias. Molecularly, this phenotype is mediated by Nol3-/--induced JAK-STAT activation and downstream activation of cyclin-dependent kinase 6 (Cdk6) and Myc. Nol3-/- MPN Thy1+LSK cells share significant molecular similarities with primary CD34+ cells from PMF patients. Furthermore, NOL3 levels are decreased in CD34+ cells from PMF patients, and the NOL3 locus is deleted in a subset of patients with myeloid malignancies. Our results reveal a novel genetic PMF-like mouse model and identify a tumor suppressor role for NOL3 in the pathogenesis of myeloid malignancies.
“A ‘Trojan Horse’ Bispecific Antibody Strategy Broadly Protects Against Ebolaviruses”
Mentor: Dr. Kartik Chandran, Department of Microbiology & Immunology
Ebola virus (EBOV) and related filoviruses are associated with sporadic outbreaks of highly lethal hemorrhagic fever in Middle and West Africa. The recent EBOV outbreak in West Africa has underscored the urgent need for antiviral treatments and demonstrated the potential of passive immunotherapy to reverse advanced filovirus disease. However, existing monoclonal antibody (mAb) cocktails such as ZMapp are limited by a narrow spectrum of antiviral action, which stems from viral strain-specific neutralization of the highly variable entry glycoprotein (GP) by most mAbs. Accordingly, we sought to develop an immunotherapeutic strategy targeting the broadly required and highly conserved interaction between GP and the filovirus entry receptor Niemann-Pick C1 (NPC1). Unfortunately, this strategy faces a critical obstacle—the GP-NPC1 interaction can occur only upon viral uptake into intracellular endosomal compartments that are poorly accessible to extracellular antibodies. To overcome this obstacle, we generated bispecific Abs (bsAbs) that combine both antiviral and anti-receptor specificities in the same molecule. The bsAbs broadly and potently neutralized viral infection in vitro in a manner that required both their engagement of GP in extracellular virions and intracellular blockade of the GP-NPC1 interaction. Our findings suggest a novel two-step mechanism of action in which the bsAbs exploit extracellular virus particles to gain access to NPC1-containing endosomes. Preliminary studies in mouse models of filovirus challenge indicated that bispecific antibodies targeting the intracellular virus-receptor interaction can afford broad in vivo protection against ebolaviruses.