Biology subjects

Cheung, L. S.

Publications and source records attributed to Cheung, L. S..

9 recordsLinked to original sources

bioRxiv2023

The Arabidopsis SWEET1 and SWEET2 uniporters recognize similar substrates despite differences in subcellular localization

Sugars Will Eventually be Exported Transporters (SWEETs) are central for sugar allocation in plants. The SWEET family is vast, with approximately 20 homologs in most plant genomes. Despite extensive research on their structures and molecular functions, it is still unclear how diverse SWEETs recognize their substrates. Previous work using SweetTrac1, a biosensor constructed by the intramolecular fusion of a conformation-sensitive fluorescent protein in the plasma membrane transporter SWEET1 from Arabidopsis thaliana, identified common features in the transporters substrates. Here, we report SweetTrac2, a new biosensor based on the Arabidopsis vacuole membrane transporter SWEET2 and use it to explore the substrate specificity of this second protein. Our results show that SWEET1 and SWEET2 recognize similar substrates but some with different affinities. Sequence comparison and mutagenesis analysis support the conclusion that the differences in affinity depend on non-specific interactions involving key residues in the binding pocket. Furthermore, SweetTrac2 can be an effective tool for monitoring sugar transport at vacuolar membranes that would be otherwise challenging to study.

biochemistry↗

bioRxiv2022

Lung tumor-infiltrating Treg have divergent transcriptional profiles and function linked to checkpoint blockade response

Regulatory T cells (Treg) are conventionally viewed to suppress endogenous and therapyinduced anti-tumor immunity; however, their role in modulating responses to immune checkpoint blockade (ICB) is unclear. In this study, we integrated single-cell RNAseq/TCRseq of >73,000 tumor-infiltrating Treg (TIL-Treg) from anti-PD-1-treated and treatment naive non-small cell lung cancers (NSCLC) with single cell analysis of tumor-associated antigen (TAA)-specific Treg derived from a murine tumor model. We identified 10 subsets of human TIL-Treg, most of which have high concordance with murine TIL-Treg subsets. Notably, one subset selectively expresses high levels of OX40 and GITR, whose engangement by cognate ligand mediated proliferative programs and NF-kB activation, as well as multiple genes involved in Treg suppression, in particular LAG3. Functionally, the OX40hiGITRhi subset in the most highly suppressive ex vivo and Treg expression of OX40, GITR and LAG3, correlated with resistance to PD-1 blockade. Surprisingly, in the murine tumor model, we found that virtually all TIL-Treg expressing T cell receptors that are specific for TAA fully develop a distinct Th1-like signature over a two-week period after entry into the tumor, down-regulating FoxP3 and up-regulating expression of TBX21 (Tbet), IFN{gamma} and certain pro-inflammatory granzymes. Application of a gene score from the murine TAA-specific Th1-like Treg subset to the human single-cell dataset revealed a highly analogous subcluster that was enriched in anti-PD-1 responding tumors. These findings demonstrate that TIL-Treg partition into multiple distinct transcriptionally-defined subsets with potentially opposing effects on ICB-induced anti-tumor immunity and suggest that TAA-specific TIL-Treg may positively contribute to anti-tumor responses. One-Sentence SummaryWe define 10 subsets of lung cancer-infiltrating regulatory T cells, one of which is highly suppressive and enriched in anti-PD-1 non-responders and the other is Th1-like and is enriched in PD-1 responders.

immunology↗

bioRxiv2022

Engineered human cytokine/antibody fusion proteins expand regulatory T cells and confer autoimmune disease protection

Low dose human interleukin-2 (hIL-2) treatment is used clinically to treat autoimmune disorders due to the cytokines preferential expansion of immunosuppressive regulatory T cells (TRegs). However, high toxicity, short serum half-life, and off-target immune cell activation limit the clinical potential of IL-2 treatment. Recent work showed that complexes comprising hIL-2 and the anti-hIL-2 antibody F5111 overcome these limitations by preferentially stimulating TRegs over immune effector cells. Although promising, therapeutic translation of this approach is complicated by the need to optimize dosing ratios and by the instability of the cytokine/antibody complex. We leveraged structural insights to engineer a single-chain hIL-2/F5111 antibody fusion protein, termed F5111 immunocytokine (IC), that potently and selectively activates and expands TRegs. F5111 IC conferred protection in mouse models of colitis and checkpoint inhibitor-induced diabetes mellitus. These results provide a roadmap for IC design and establish a TReg-biased immunotherapy that could be clinically translated for autoimmune disease treatment.

bioengineering↗

bioRxiv2020

Tuning of self-renewing capacity in theArabidopsis stomatal lineage by hormonaland nutrition regulation of asymmetric celldivisions

Asymmetric and self-renewing divisions build and pattern tissues. In the Arabidopsis thaliana stomatal lineage, asymmetric cell divisions, guided by polarly localized cortical proteins, generate the majority of cells on the leaf surface. These divisions can be fine-tuned by systemic and environmental signals to modify tissue development, but the molecular mechanisms by which plants incorporate such cues to regulate asymmetric divisions are largely unknown. In a screen for modulators of cell polarity and asymmetric divisions, we identified a mutation in CONSTITIUTIVE TRIPLE RESPONSE 1, a negative regulator of ethylene signaling. We subsequently revealed antagonistic impacts of ethylene and glucose signaling on the self-renewing capacity of stomatal lineage stem cells. Quantitative analysis of the impacts of these signaling systems on cell polarity and fate dynamics showed that developmental information may be encoded in both the spatial and temporal asymmetries of polarity proteins. Taken together, our results provide a framework for a mechanistic understanding of how systemic information such as nutritional status and environmental factors tune stem cell behavior in the stomatal lineage, ultimately enabling optimization of leaf size and cell-type composition.

plant biology↗

bioRxiv2020

Quantitative and dynamic cell polarity tracking in plant cells

Quantitative information on the spatiotemporal distribution of polarized proteins is central for understanding cell-fate determination, yet collecting sufficient data for statistical analysis is difficult to accomplish with manual measurements. Here we present POME, a semi-automated pipeline for the quantification of cell polarity, and demonstrate its application to a variety of developmental contexts. POME analysis reveals that during asymmetric cell divisions in the Arabidopsis thaliana stomatal lineage, polarity proteins BASL and BRXL2 are more asynchronous and less mutually dependent than previously thought. While their interaction is important to maintain their polar localization and recruit other effectors to regulate asymmetric cell divisions, BRXL2 polarization precedes that of BASL and can be initiated in BASLs absence. Uncoupling of polarization from BASL activity is also seen in Brachypodium distachyon, where we find that the MAPKKK BdYDA1 is segregated and polarized following asymmetric division. Our results demonstrate that POME is a versatile tool, which by itself or combined with tissue-level studies and advanced microscopy techniques can help uncover new mechanisms of cell polarity.

cell biology↗

bioRxiv2020

Quantitative analysis of transporter activity biosensors

The allocation of sugars from photosynthetic leaves to storage tissues in seeds, fruits, and tubers is an important determinant of crop yields. Genetically guided selection and transgenic modification of plant membrane transporters can help enhance crop yields and increase pathogen resistance. Yet, quantitative, systems-level models to support this effort are lacking. Recently, biosensors gained popularity for collecting spatiotemporally resolved information on cell physiology and validating computational models. Here, we report the design and use of genetically-encoded biosensors to measure the activity of SWEETs, the only family of sugar transporters known to facilitate the cellular release of sugar in plants. We created SweetTrac sensors by inserting circularly-permutated GFP into SWEET transporters, resulting in chimeras that translate substrate-triggered conformational rearrangements during the transport cycle into detectable changes in fluorescence intensity. We demonstrate that a combination of cell sorting and bioinformatics can be applied as a general approach to accelerate the design of biosensors for in vivo biochemistry. Finally, mass action kinetics analysis of the biosensors response suggests that SWEETs are low-affinity, near-symmetric transporters that can rapidly equilibrate intra- and extracellular concentrations of sugars. Significance StatementTransporters are the gatekeepers of the cell. Transporters facilitate the exchange of ions and metabolites between cellular and subcellular compartments, thus controlling processes from bacterial chemotaxis to the release of neurotransmitters. In plants, transporters play critical roles in the allocation of carbon to different organs. Biosensors derived from transporters have been generated to monitor the activity of these proteins within the complex environment of the cell. However, a quantitative framework that reconciles molecular and cellular-level events to help interpret the response of biosensors is still lacking. Here, we created novel sugar transport biosensors and formulated a mathematical model to explain their response. These types of models can help realize multiscale, dynamic simulations of metabolite allocation to guide crop improvement.

bioengineering↗

bioRxiv2020

IL-4 receptor targeting as an effective immunotherapy against triple-negative breast cancer

In many solid tumors including triple-negative breast cancer (TNBC), IL-4 receptor (IL-4R) upregulation has been shown to promote cancer cell proliferation, apoptotic resistance, metastatic potential and a Th2 response in the tumor microenvironment (TME). Immunosuppressive cells in the TME including myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) also express the IL4-R. We hypothesized that selective depletion of IL4-R bearing cells in TNBC may have dual cytotoxic and immunotherapeutic benefit. To selectively target IL-4R+ cells, we genetically constructed, expressed and purified DABIL-4, a fusion protein toxin consisting of the catalytic and translocation domains of diphtheria toxin fused to murine IL-4. We found that DABIL-4 has potent and specific cytotoxic activity against TNBC cells in vitro. In murine TNBC models, DABIL-4 significantly reduced tumor growth, splenomegaly and lung metastases, and this was associated with reductions in MDSC, TAM and regulatory T-cells (Tregs) populations with a concomitant increase in the proportion of IFN{gamma}+ CD8 T-cells. The anti-tumor activity of DABIL-4 was absent in IL-4R KO mice directly implicating IL-4R directed killing as the mechanism of anti-tumor activity. Moreover, NanoString analysis of DABIL-4 treated TNBC tumors revealed marked decline in mRNA transcripts that promote tumorigenesis and metastasis. Our findings demonstrate that DABIL-4 is a potent targeted antitumor agent which depletes both IL-4R bearing tumor cells as well as immunosuppressive cell populations in the TME. STATEMENT OF SIGNIFICANCEIn solid tumors like breast cancer, Interleukin-4 receptor (IL-4R) expression in the tumor microenvironment aids tumor growth and metastasis. IL-4R expression upon host immune cells further dampens antitumor immunity. In this study, we have genetically constructed a fusion protein toxin, DABIL-4, composed of the catalytic and translocation domains of diphtheria toxin and murine IL-4. DABIL-4 showed specific cytotoxicity against triple-negative breast cancer (TNBC) cells in vitro. DABIL-4 also markedly inhibited TNBC tumor growth and metastasis in vivo. The primary activity of DABIL-4 was found to be depletion of IL-4R+ immune cells in combination with direct elimination of tumor cells. In conclusion, DABIL-4 targeting of both tumor and immunosuppressive host cells is a versatile and effective treatment strategy for TNBC.

immunology↗

bioRxiv2018

GRIBCG: A software for selection of sgRNAs in the design of balancer chromosomes

BackgroundBalancer chromosomes are tools used by fruit fly geneticists to prevent meiotic recombination. Recently, CRISPR/Cas9 genome editing has been shown capable of generating inversions similar to the chromosomal rearrangements present in balancer chromosomes. Extending the benefits of balancer chromosomes to other multicellular organisms could significantly accelerate biomedical and plant genetics research.\n\nResultsHere, we present GRIBCG (Guide RNA Identifier for Balancer Chromosome Generation), a tool for the rational design of balancer chromosomes. GRIBCG identifies single guide RNAs (sgRNAs) for use with Streptococcus pyogenes Cas9 (SpCas9). These sgRNAs would efficiently cut a chromosome multiple times while minimizing off-target cutting in the rest of the genome. We describe the performance of this tool on six model organisms and compare our results to two routinely used fruit fly balancer chromosomes.\n\nConclusionGRIBCG is the first of its kind tool for the design of balancer chromosomes using CRISPR/Cas9. GRIBCG can accelerate genetics research by providing a fast, systematic and simple to use framework to induce chromosomal rearrangements.

bioinformatics↗

bioRxiv2018

A second generation IL-2 receptor-targeted diphtheria fusion toxin exhibits anti-tumor activity and synergy with anti-PD-1 in melanoma

Denileukin diftitox (DAB1-389-IL-2, Ontak(R)) is a diphtheria toxin-based fusion protein that depletes CD25-positive cells including regulatory T cells (Tregs) and was approved for the treatment of persistent or recurrent cutaneous T cell lymphoma. However, the clinical use of denileukin diftitox was limited by vascular leak toxicity and production issues related to drug aggregation and purity. We found that a single amino acid substitution (V6A) in a motif associated with vascular leak induction yields a fully active, second-generation biologic, s-DAB1-386-IL-2(V6A), which elicits 50-fold less HUVEC monolayer permeation and is 3.7-fold less lethal to mice by LD50 analysis than s-DAB1-386-IL-2 Additionally, to overcome aggregation problems, we developed a novel production method for the fusion toxin using Corynebacterium diphtheriae that secretes fully-folded, biologically active, monomeric s-DAB1-386-IL-2 into the culture medium. Using the poorly immunogenic mouse B16F10 melanoma model, we initiated treatment 7 days after tumor challenge and observed that, while both s-DAB1-386-IL-2(V6A) and s-DAB1-386-IL-2 are inhibitors of tumor growth, the capacity to treat with higher doses of s-DAB1-386-IL-2(V6A) could provide a superior activity window. In a sequential dual therapy study in tumors that have progressed for 10 days both s-DAB1-386-IL-2(V6A) and s-DAB1-386-IL-2 given prior to checkpoint inhibition with anti-PD-1 antibodies inhibited tumor growth, while either drug given as monotherapy had less effect. s-DAB1-386-IL-2(V6A), a fully monomeric protein with reduced vascular leak, is a second-generation diphtheria toxin-based fusion protein with promise as a cancer immunotherapeutic both alone and in conjunction with PD-1 blockade.\n\nSignificance StatementRegulatory T cells (Tregs) infiltrate tumors in various cancers and promote an immunosuppressive microenvironment that hinders anti-tumor immunity. Denileukin diftitox, a diphtheria toxin-based fusion protein that depletes Tregs, was approved for the treatment of T cell malignancies, but its clinical use was limited due to the presence of protein aggregates and toxicity associated with vascular leakage. Here we report the production of a second generation IL-2 receptor-targeted, fully-folded, monomeric diphtheria fusion toxin, and a V6A mutant variant which showed reduced vascular leak in vitro and reduced lethality in mice. In a mouse model of melanoma, we found significant decrease in tumor growth associated with reduction in Tregs when the protein was tested as monotherapy or in combination with checkpoint blockade.

cancer biology↗