Biology subjects

Brown, W.

Publications and source records attributed to Brown, W..

13 recordsLinked to original sources

bioRxiv2025

Structural basis for lipid binding by the blood protein vitronectin, a component of HDL

Vitronectin (Vn) is a multifunctional blood glycoprotein involved in cell adhesion and migration, blood coagulation, and inflammation. It is a component of the high-density lipoprotein (HDL) proteome, and often found associated with the calcified, lipid-rich, protein deposits that are a hallmark of age-related macular degeneration, Alzheimers disease, atherosclerosis and other aging-related diseases. Here we explored the molecular basis for lipid binding by Vn using isothermal titration calorimetry (ITC), nuclear magnetic resonance (NMR) and all-atom molecular dynamics (MD) simulations. The data reveal a hydrophobic groove on the surface of the hemopexin-like (HX) domain of Vn, that is capable of binding phosphatidylcholine (PC). Conformational landscape analyses of multiple, independent MD simulations identify key structural motifs and intermolecular contacts mediating the association of Vn with PC, and show that lipid binding is guided by interactions with positively charged and hydrophobic residues that organize the lipids in a tail-to-tail bilayer-like arrangement within the groove. Collectively, the data establish a comprehensive structural model for Vn association with HDL and provide mechanistic insight into its accumulation within lipid-rich deposits characteristic of age-related pathologies.

biophysics↗

bioRxiv2024

Nucleoprotein phase-separation affinities revealed via atomistic simulations of short peptide and RNA fragments

Liquid-liquid phase separation of proteins and nucleic acids into condensate phases is a versatile mechanism for ensuring compartmentalization of cellular biochemistry. RNA molecules play critical roles in these condensates, particularly in transcriptional regulation and stress responses, exhibiting a wide range of thermodynamic and dynamic behaviors. However, deciphering the molecular grammar that governs the stability and dynamics of protein-RNA condensates remains challenging due to the multicomponent and heterogeneous nature of these biomolecular mixtures. In this study, we employ atomistic simulations of twenty distinct mixtures containing minimal RNA and peptide fragments to dissect the phase-separating affinities of all twenty amino acids in the presence of RNA. Our findings elucidate chemically specific interactions, hydration profiles, and ionic effects that synergistically promote or suppress protein-RNA phase separation. We map a ternary phase diagram of interactions, identifying four distinct groups of residues that promote, maintain, suppress, or disrupt protein-RNA clusters.

biophysics↗

bioRxiv2024

Decoupling Coldness and Softness in Tactile Wetness Perception Using Tunable Hydrogels

This study investigates the perception of tactile wetness, a complex sensation experienced by humans. Previous research has primarily focused on either thermal or mechanical cues separately, or has used textiles as stimuli whose parameters are difficult to control. Here, we employed polyacrylamide hydrogels with varying stiffness levels soaked in liquids of distinct thermal conductivities. By psychophysically evaluating participants perception of wetness, we showed that the wetness judgments for the samples exhibit a transitive relationship based on the mechanical and thermal cues from an intrinsically tunable organic material. We developed a prediction model of human wetness judgment with an accuracy of 90% and found that the best metrics for the most accurate model were those that were the most human-adjacent: change in temperature at the skin-sample interface (thermal) and compressive force from 2 mm indentation of the sample (mechanical). Given these parameters, we developed a perceptual space capable of recreating 7 distinct levels of wetness perception with the physical parameters used in this study. The results provide insights into the relative contributions of mechanical and thermal stimulus properties in wetness perception. Most notably, this work highlights that the physical characteristics of the skin-stimulus interface can provide ample information for creating a wetness perceptual space, as opposed to the chemical composition of the hydrogels.

neuroscience↗

bioRxiv2023

MKP1 promotes nonalcoholic steatohepatitis by suppressing AMPK activity through LKB1 nuclear retention

Nonalcoholic steatohepatitis (NASH) is triggered by hepatocyte death through activation of caspase 6, as a result of decreased adenosine monophosphate (AMP)-activated protein kinase-alpha (AMPK) activity. Increased hepatocellular death promotes inflammation which drives hepatic fibrosis. We show that the nuclear-localized mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP1) is upregulated in NASH patients and in NASH diet fed mice. The focus of this work was to investigate whether and how MKP1 is involved in the development of NASH. Under NASH conditions increased oxidative stress, induces MKP1 expression leading to nuclear p38 MAPK dephosphorylation and decreased liver kinase B1 (LKB1) phosphorylation at a site required to promote LKB1 nuclear exit. Hepatic deletion of MKP1 in NASH diet fed mice released nuclear LKB1 into the cytoplasm to activate AMPK and prevent hepatocellular death, inflammation and NASH. Hence, nuclear-localized MKP1-p38 MAPK-LKB1 signaling is required to suppress AMPK which triggers hepatocyte death and the development of NASH.

physiology↗

bioRxiv2022

Optogenetic Protein Cleavage in Zebrafish Embryos

A wide array of optogenetic tools is available that allow for precise spatiotemporal control over many cellular processes. These tools have been especially popular among zebrafish researchers who take advantage of the embryos transparency. However, photocleavable optogenetic proteins have not been utilized in zebrafish. We demonstrate successful optical control of protein cleavage in embryos using PhoCl, a photocleavable fluorescent protein. This optogenetic tool offers temporal and spatial control over protein cleavage events, which we demonstrate in light-triggered protein translocation and apoptosis.

synthetic biology↗

bioRxiv2022

Mutational impact of APOBEC3B and APOBEC3A in a human cell line

A prominent source of mutation in cancer is single-stranded DNA cytosine deamination by cellular APOBEC3 enzymes, which results in signature C-to-T and C-to-G mutations in TCA and TCT motifs. Although multiple enzymes have been implicated, reports conflict and it is unclear which protein(s) are responsible. Here we report the development of a selectable system to quantify genome mutation and demonstrate its utility by comparing the mutagenic activities of three leading candidates - APOBEC3A, APOBEC3B, and APOBEC3H. The human cell line, HAP1, is engineered to express the thymidine kinase (TK) gene of HSV-1, which confers sensitivity to ganciclovir. Expression of APOBEC3A and APOBEC3B, but not catalytic mutant controls or APOBEC3H, triggers increased frequencies of TK mutation and nearly indistinguishable TC-biased cytosine mutation profiles in the selectable TK reporter gene. Whole genome sequences from TK mutant clones enabled an analysis of thousands of single base substitution mutations and extraction of local sequence preferences with APOBEC3A preferring YTCW motifs over 70% of the time and APOBEC3B just under 50% of the time (Y=C/T; W=A/T). Signature comparisons with breast tumor whole genome sequences indicate that most malignancies manifest intermediate percentages of APOBEC3 signature mutations in YTCW motifs, mostly between 50 and 70%, suggesting that both enzymes are contributing in a combinatorial manner to the overall mutation landscape. Although the vast majority of APOBEC3A- and APOBEC3B-induced single base substitution mutations occur outside of predicted chromosomal DNA hairpin structures, whole genome sequence analyses and supporting biochemical studies also indicate that both enzymes are capable of deaminating the single-stranded loop regions of DNA hairpins at elevated rates relative to control conditions. These studies combine to help resolve a long-standing etiologic debate on the source of APOBEC3 signature mutations in cancer and indicate that future diagnostic and therapeutic efforts should focus on both APOBEC3A and APOBEC3B.

cancer biology↗

bioRxiv2021

The MS remyelinating drug bexarotene (an RXR agonist) promotes induction of human Tregs and suppresses Th17 differentiation in vitro

The retinoid X receptor (RXR) agonist bexarotene has recently been shown to promote remyelination in individuals with multiple sclerosis. Murine studies demonstrated that RXR agonists can have anti-inflammatory effects by enhancing the ability of all-trans-retinoic acid (tRA), the primary active metabolite of vitamin A, to promote T regulatory cell (Treg) induction and reduce Th17 differentiation in vitro, following stimulation of naive CD4 cells in the presence of TGF-{beta}. Stimulating naive human CD4 T cells for 7 days, in the presence of either Treg or Th17 skewing cytokines {+/-} bexarotene (1 M), {+/-} other RXR agonists (9CisRA and NRX 194204), or {+/-} tRA (100 nM) shows that RXR agonists, including bexarotene, are capable of tipping the human Treg/Th17 axis in favour of Treg induction. Furthermore, this occurs independently of tRA and retinoic acid receptor (RAR) signalling. Tregs induced in the presence of bexarotene express many of the canonical markers of T cell regulation and are functionally suppressive in vitro. These findings support a potential immunomodulatory role for bexarotene and highlight the possible therapeutic application of RXR agonists in autoimmune disease, with bexarotenes pro-remyelinating effects making multiple sclerosis a particularly attractive disease target. Significance StatementThe pan-retinoid X receptor (RXR) agonist bexarotene has recently been shown to promote remyelination in patients with multiple sclerosis. Here we demonstrate that bexarotene, and other RXR agonists have immunomodulating effects, tipping the Th17/T regulatory cell (Treg) differentiation axis in favour of Treg development. These findings lend support to the idea of developing RXR agonists as treatments of autoimmune diseases, in particular multiple sclerosis.

immunology↗

bioRxiv2020

APOBEC3B expression generates an immunogenic model of Kras mutant lung cancer

Mutations in oncogenes such as KRAS and EGFR cause a high proportion of lung cancers. Drugs targeting these proteins cause tumour regression but ultimately fail to cure these cancers, leading to intense interest in how best to combine them with other treatments, such as immunotherapies. However, preclinical systems for studying the interaction of lung tumours with the host immune system are inadequate, in part due to the low tumour mutational burden in genetically engineered mouse models. Here we set out to develop mouse models of mutant KRAS-driven lung cancer with an elevated tumour mutational burden by expressing the human DNA cytosine deaminase, APOBEC3B, to mimic the mutational signature seen in human lung cancer. This failed to substantially increase clonal tumour mutational burden and autochthonous tumours remained refractory to immunotherapy. However, by establishing clonal cell lines from these tumours we generated an immunogenic syngeneic transplantation model of KRAS mutant lung adenocarcinoma that was sensitive to immunotherapy. Unexpectedly, we found that anti-tumour immune responses were not directed against neoantigens but instead targeted derepressed endogenous retroviral antigens. The ability of KRASG12C inhibitors to cause regression of KRASG12C-expressing versions of these tumours was markedly potentiated by the adaptive immune system, providing a unique opportunity for the study of combinations of targeted and immunotherapies in immune-hot lung cancer.

cancer biology↗

bioRxiv2019

Spatiotemporal Control of CRISPR/Cas9 Function in Cells and Zebrafish using Light-Activated Guide RNA

We developed a new method for conditional regulation of CRISPR/Cas9 activity in mammalian cells and zebrafish embryos via photochemically activated, caged guide RNAs. Caged gRNAs are generated by substituting four nucleobases evenly distributed throughout the 5-protospacer region with caged nucleobases during synthesis. Caging confers complete suppression of gRNA:target dsDNA hybridization and rapid restoration of CRISPR/Cas9 function upon optical activation. This tool offers simplicity and complete programmability in design, high spatiotemporal specificity in cells and zebrafish embryos, excellent off to on switching, and stability by preserving the ability to form Cas9:gRNA ribonucleoprotein complexes. caged gRNAs are novel tools for conditional control of gene editing thereby enabling the investigation of spatiotemporally complex physiological events by obtaining a better understanding of dynamic gene regulation.

developmental biology↗

bioRxiv2019

A rabbit monoclonal antibody against the antiviral and cancer genomic DNA mutating enzyme APOBEC3B

The DNA cytosine deaminase APOBEC3B (A3B) is normally an antiviral factor in the innate immune response. However, A3B has been implicated in cancer mutagenesis, particularly in solid tumors of the bladder, breast, cervix, head/neck, and lung. Here, we report data on the generation and characterization of a rabbit monoclonal antibody (mAb) for human A3B through a series of immunoblot, immunofluorescence microscopy, and immunohistochemistry experiments. Positive results indicate that one mAb, 5210-87-13, will be useful for fundamental research in virology and cancer biology and that immunohistochemical quantification of A3B enzyme levels may constitute a clinical biomarker for tumor evolvability and differential treatment.

cancer biology↗

bioRxiv2018

Using natural language processing and machine learning to classify health literacy from secure messages: The ECLIPPSE study

Limited health literacy can be a barrier to healthcare delivery, but widespread classification of patient health literacy is challenging. We applied natural language processing and machine learning on a large sample of 283,216 secure messages sent from 6,941 patients to their clinicians for this study to develop and validate literacy profiles as indicators of patients health literacy. All patients were participants in Kaiser Permanente Northern Californias DISTANCE Study. We created three literacy profiles, comparing performance of each literacy profile against a gold standard of patient self-report. We also analyzed associations between the literacy profiles and patient demographics, health outcomes and healthcare utilization. T-tests were used for numeric data such as A1C, Charlson comorbidity index and healthcare utilization rates, and chi-square tests for categorical data such as sex, race, continuous medication gaps and severe hypoglycemia. Literacy profiles varied in their test characteristics, with C-statistics ranging from 0.61-0.74. Relationships between literacy profiles and health outcomes revealed patterns consistent with previous health literacy research: patients identified via literacy profiles as having limited health literacy were older and more likely minority; had poorer medication adherence and glycemic control; and higher rates of hypoglycemia, comorbidities and healthcare utilization. This research represents the first successful attempt to use natural language processing and machine learning to measure health literacy. Literacy profiles offer an automated and economical way to identify patients with limited health literacy and a greater vulnerability to poor health outcomes.

bioinformatics↗

bioRxiv2018

Biased signaling downstream of epidermal growth factor receptor regulates proliferative versus apoptotic response to ligand

Inhibition of EGFR signaling by small molecule kinase inhibitors and monocloncal antibodies has proven effective in the treatment of multiple cancers. In contrast, metastatic breast cancers (BC) derived from EGFR-expressing mammary tumors are inherently resistant to EGFR-targeted therapies. Mechanisms that contribute to this inherent resistance remain poorly defined. Here we show that in contrast to primary tumors, ligand-mediated activation of EGFR in metastatic BC is dominated by STAT1 signaling. This change in downstream signaling leads to apoptosis and growth inhibition in response to EGF in metastatic BC cells. Mechanistically, these changes in downstream signaling result from an increase in the internalized pool of EGFR in metastatic cells, increasing physical access to the nuclear pool of STAT1. Along these lines, an EGFR mutant that is defective in endocytosis is unable to elicit STAT1 phosphorylation and apoptosis. Additionally, inhibition of endosomal signaling using an EGFR inhibitor linked to a nuclear localization signal specifically prevents EGF-induced STAT1 phosphorylation and cell death, without affecting EGFR:ERK1/2 signaling. Pharmacologic blockade of ERK1/2 signaling through the use of the allosteric MEK1/2 inhibitor, trametinib, dramatically biases downstream EGFR signaling toward a STAT1 dominated event, resulting in enhanced EGF-induced apoptosis in metastatic BC cells. Importantly, combined administration of trametinib and EGF also facilitated an apoptotic switch in EGFR-transformed primary tumor cells, but not normal mammary epithelial cells. These studies reveal a fundamental distinction for EGFR function in metastatic BC. Furthermore, the data demonstrate that pharmacological biasing of EGFR signaling toward STAT1 activation is capable of revealing the apoptotic function of this critical pathway.

cancer biology↗

bioRxiv2017

The Antiviral and Cancer Genomic DNA Deaminase APOBEC3H Is Regulated by a RNA-Mediated Dimerization Mechanism

Human APOBEC3H and homologous single-stranded DNA cytosine deaminases are unique to mammals. These DNA editing enzymes function in innate immunity by restricting the replication of viruses and transposons. Misregulated APOBEC3H also contributes to cancer mutagenesis. Here we address the role of RNA in APOBEC3H regulation. APOBEC3H co-purifies with RNA as an inactive protein, and RNase A treatment yields enzyme preparations with stronger DNA deaminase activity. RNA binding-defective mutants are DNA hypermutators. Chromatography profiles and crystallographic data demonstrate a mechanism in which double-stranded RNA mediates enzyme dimerization. RNA binding is required for APOBEC3H cytoplasmic localization and for packaging into HIV-1 particles and antiviral activity. Related DNA deaminases including other APOBEC3 family members and the antibody gene diversification enzyme AID also bind RNA and are predicted to have a similar RNA binding motif suggesting mechanistic conservation and relevance to innate and adaptive immunity and to multiple diseases.\n\nHIGHLIGHTSRNA inhibits human APOBEC3H DNA cytosine deaminase activity\n\nRNA binding mutants are DNA hypermutators\n\nX-ray structure demonstrates an RNA duplex-mediated APOBEC3H dimerization mechanism\n\nRNA binding is required for packaging into HIV-1 particles and antiviral activity

microbiology↗