Biology subjects

Porter, D. F.

Publications and source records attributed to Porter, D. F..

10 recordsLinked to original sources

bioRxiv2025

Thermal proteome profiling identifies glucose binding proteins involved in metabolic disease

Recent work has shown that glucose can directly bind non-enzymatic proteins to modulate their function. We sought to build on this work by adapting thermal proteome profiling screens to uncover novel glucose interactors involved in metabolism. Proteome integral solubility alternation (PISA) profiling nominated 23 proteins with glucose-induced thermal solubility, including two proteins strongly implicated in metabolic disease, TSC22D4 and IGF2BP2. First, we characterized glucose binding of TSC22D4, an intrinsically disordered leucine zipper protein strongly implicated in hepatic steatosis. MST confirmed direct glucose-protein interaction of TSC22D4. UV-crosslinking mass spectrometry identified putative glucose binding at the C-terminal leucine zipper. Mutating isoleucine 322 to tryptophan (I322W) abolishes glucose binding. Crosslinking-MS and chemo-proteomic experiments suggest that glucose increases accessibility of the leucine zipper region, resulting in intra-protein contacts between C-terminal zipper domain and N-terminal intrinsically-disordered domain. TSC22D4 associates with fatty acid metabolism machinery proteins in response to high glucose conditions, suggesting a possible role for TSC22D4 in altering fatty acid metabolism. Next, we characterized glucose-binding in IGF2BP2, an RNA-binding protein essential for beta cell insulin secretion. We first confirmed direct IGF2BP2-glucose interaction and created glucose-binding mutant Y40A based on computational docking predictions. IGF2BP2Y40A exhibited a dominant negative impact on proliferation and insulin secretion in MIN6-6 beta cells. Glucose increased IGF2BP2 binding to client mRNAs Igf2 and Pdx1, which has previously been demonstrated to mediate its impact on insulin secretion. Thus, our data suggests that IGF2BP2 directly binds glucose to enhance insulin secretion.

biochemistry↗

bioRxiv2025

The Adhesion GPCR ADGRL2 engages Gα13 to Enable Epidermal Differentiation

Homeostasis relies on signaling networks controlled by cell membrane receptors. Although G-protein-coupled receptors (GPCRs) are the largest family of transmembrane receptors, their specific roles in the epidermis are not fully understood. Dual CRISPR-Flow and single cell Perturb-seq knockout screens of all epidermal GPCRs were thus performed, uncovering an essential requirement for adhesion GPCR ADGRL2 (latrophilin 2) in epidermal differentiation. Among potential downstream guanine nucleotide-binding G proteins, ADGRL2 selectively activated G13. Perturb-seq of epidermal G proteins and follow-up tissue knockouts verified that G13 is also required for epidermal differentiation. A cryo-electron microscopy (cryo-EM) structure in lipid nanodiscs showed that ADGRL2 engages with G13 at multiple interfaces, including via a novel interaction between ADGRL2 intracellular loop 3 (ICL3) and a G13-specific QQQ glutamine triplet sequence in its GTPase domain. In situ gene mutation of this interface sequence impaired epidermal differentiation, highlighting an essential new role for an ADGRL2-G13 axis in epidermal differentiation.

cell biology↗

bioRxiv2024

Disease-Linked Regulatory DNA Variants and Homeostatic Transcription Factors in Epidermis

Identifying noncoding single nucleotide variants (SNVs) in regulatory DNA linked to polygenic disease risk, the transcription factors (TFs) they bind, and the target genes they dysregulate is a goal in polygenic disease research. Massively parallel reporter gene analysis (MPRA) of 3,451 SNVs linked to risk for polygenic skin diseases characterized by disrupted epidermal homeostasis identified 355 differentially active SNVs (daSNVs). daSNV target gene analysis, combined with daSNV editing, underscored dysregulated epidermal differentiation as a pathomechanism shared across common polygenic skin diseases. CRISPR knockout screens of 1772 human TFs revealed 108 TFs essential for epidermal progenitor differentiation, uncovering novel roles for ZNF217, CXXC1, FOXJ2, IRX2 and NRF1. Population sampling CUT&RUN of 27 homeostatic TFs identified allele-specific DNA binding (ASB) differences at daSNVs enriched near epidermal homeostasis and monogenic skin disease genes, with notable representation of SP/KLF and AP-1/2 TFs. This resource implicates dysregulated differentiation in risk for diverse polygenic skin diseases.

genetics↗

bioRxiv2024

Iron-sensitive RNA regulation by poly C binding proteins

Iron is essential for normal cellular function. Homeostatic responses to low iron availability have long been known to rely on posttranscriptional mechanisms. Poly C binding proteins (PCBPs) are essential RNA binding proteins that regulate alternative splicing, translation and RNA stability. They also serve as critical iron chaperones that manage intracellular iron flux. However, the impact of cellular iron levels on the PCBP-directed transcriptome has not been globally evaluated. We have found broad transcriptome changes in response to low iron availability consistent with numerous operant posttranscriptional mechanisms that sense iron. By comparing gene expression and alternative splicing directed by PCBPs to the iron-sensitive transcriptome, we found genes with iron-sensitive PCBP RNA regulation. Further, we demonstrate that cellular iron levels impact PCBP1 RNA binding. Our data show a large-scale RNA regulatory response to cellular iron levels and open the possibility for other iron-sensitive RNA binding proteins.

molecular biology↗

bioRxiv2021

Modified forms of easyCLIP

The easyCLIP protocol describes a method for both normal CLIP library construction and the absolute quantification of RNA cross-linking rates, data which could be usefully combined to analyze RNA-protein interactions. Using these cross-linking metrics, significant interactions could be defined relative to a set of random non-RBPs. The original easyCLIP protocol did not use index reads, required custom sequencing primers, and did not have an easily reproducible analysis workflow. This short paper attempts to amend these deficiencies. It also includes some additional technical experiments and investigates the usage of alternative adapters. The results here are intended to allow more options to easily perform and analyze easyCLIP.

molecular biology↗

bioRxiv2019

Records of RNA localization through covalent tagging

RNA movements and localization pervade biology, from embryonic development to disease. To identify RNAs at specific subcellular locations, we anchored a uridine-adding enzyme at those sites, which then marked RNAs in its vicinity with 3 terminal uridines. RNAs were tagged independent of their translation status, and included not only mRNAs, but also ncRNAs and ncRNA processing intermediates. A battery of RNAs, including the stress sensor, IRE1, were tagged at both ER and mitochondria, and reveal RNAs whose dual localization is conserved from yeast to human cells.

genomics↗

bioRxiv2019

easyCLIP Quantifies RNA-Protein Interactions and Characterizes Recurrent PCBP1 Mutations in Cancer

RNA-protein interactions mediate a host of cellular processes, underscoring the need for methods to quantify their occurrence in living cells. RNA interaction frequencies for the average cellular protein are undefined, however, and there is no quantitative threshold to define a protein as an RNA-binding protein (RBP). Ultraviolet (UV) cross-linking immunoprecipitation (CLIP)-sequencing, an effective and widely used means of characterizing RNA-protein interactions, would particularly benefit from the capacity to quantitate the number of RNA cross-links per protein per cell. In addition, CLIP-seq methods are difficult, have high experimental failure rates and many ambiguous analytical decisions. To address these issues, the easyCLIP method was developed and used to quantify RNA-protein interactions for a panel of known RBPs as well as a spectrum of random non-RBP proteins. easyCLIP provides the advantages of good efficiency compared to current standards, a simple protocol with a very low failure rate, troubleshooting information that includes direct visualization of prepared libraries without amplification, and a new form of analysis. easyCLIP, which uses sequential on-bead ligation of 5 and 3 adapters tagged with different infrared dyes, classified non-RBPs as those with a per protein RNA cross-link rate of <0.1%, with most RBPs substantially above this threshold, including Rbfox1 (18%), hnRNPC (22%), CELF1 (11%), FBL (2%), and STAU1 (1%). easyCLIP with the PCBP1L100 RBP mutant recurrently seen in cancer quantified increased RNA binding compared to wild-type PCBP1 and suggested a potential mechanism for this RBP mutant in cancer. easyCLIP provides a simple, efficient and robust method to both obtain both traditional CLIP-seq information and to define actual RNA interaction frequencies for a given protein, enabling quantitative cross-RBP comparisons as well as insight into RBP mechanisms.

molecular biology↗

bioRxiv2018

Towards identifying subnetworks from FBF binding landscapes in Caenorhabditis spermatogenic or oogenic germlines

Metazoan PUF (Pumilio and FBF) RNA-binding proteins regulate various biological processes, but a common theme across phylogeny is stem cell regulation. In Caenorhabditis elegans, FBF (fem-3 Binding Factor) maintains germline stem cells regardless of which gamete is made, but FBF also functions in the process of spermatogenesis. We have begun to \"disentangle\" these biological roles by asking which FBF targets are gamete-independent, as expected for stem cells, and which are gamete-specific. Specifically, we compared FBF iCLIP binding profiles in adults making sperm to those making oocytes. Normally, XX adults make oocytes. To generate XX adults making sperm, we used a fem-3(gf) mutant requiring growth at 25{degrees}; for comparison, wild-type oogenic hermaphrodites were also raised at 25{degrees}. Our FBF iCLIP data revealed FBF binding sites in 1522 RNAs from oogenic adults and 1704 RNAs from spermatogenic adults. More than half of these FBF targets were independent of germline gender. We next clustered RNAs by FBF-RNA complex frequencies and found four distinct blocks. Block I RNAs were enriched in spermatogenic germlines, and included validated target fog-3, while Block II and III RNAs were common to both genders, and Block IV RNAs were enriched in oogenic germlines. Block II (510 RNAs) included almost all validated FBF targets and was enriched for cell cycle regulators. Block III (21 RNAs) was enriched for RNA-binding proteins, including previously validated FBF targets gld-1 and htp-1. We suggest that Block I RNAs belong to the FBF network for spermatogenesis, and that Blocks II and III are associated with stem cell functions.

developmental biology↗

bioRxiv2018

Unbiased screen of RNA tailing enzymes at single-nucleotide resolution reveals a poly(UG) polymerase required for genome integrity and RNA silencing

Ribonucleotidyl transferases (rNTases) add non-templated ribonucleotides to diverse RNAs. We developed a screening strategy in S. cerevisiae to identify sequences added by candidate enzymes from different organisms at single-nucleotide resolution. The rNTase activities of 19 previously unexplored enzymes were determined. In addition to poly(A)- and poly(U)-adding enzymes, we identified a C-adding enzyme that is likely part of a two-enzyme system that adds CCA to tRNAs in a eukaryote; a nucleotidyl transferase that adds nucleotides to RNA without apparent nucleotide preference; and a poly(UG) polymerase, C. elegans MUT-2, which adds alternating U and G nucleotides to form poly(UG) tails. MUT-2 is known to be required for certain forms of RNA silencing, and mutations in the enzyme that are defective in silencing also fail to add poly(UG) tails in our assay. We propose that MUT-2 poly(UG) polymerase activity is required to promote genome integrity and RNA silencing.

molecular biology↗

bioRxiv2016

An RNA binding polymer specifies nematode sperm fate

Metazoan germ cells develop as sperm or oocytes, depending on chromosomal sex, extrinsic signaling from somatic tissue and intrinsic factors within the germ cells. Gamete fate regulatory networks have been analyzed in nematodes, flies and mammals, but only in C. elegans have terminal intrinsic regulators been identified, which include a Tob/BTG protein family member, FOG-3. Canonical Tob/BTG proteins function as monomeric adaptor proteins that link RNA binding proteins to deadenylases. To ask if FOG-3 functions similarly, we first determined its crystal structure. FOG-3 harbors a classical Tob/BTG fold, but unlike other Tob/BTG proteins, FOG-3 dimerizes and these FOG-3 dimers assemble into polymers. The importance of FOG-3 polymers to sperm fate specification was confirmed in vivo using CRISPR/Cas9 gene editing to create mutations designed to disrupt the polymer interface. The FOG-3 surface potential is highly basic, suggesting binding to nucleic acid. We find that FOG-3 binds RNA directly with a strong preference for 3UTRs of oogenic mRNAs. Our results reveal a divergent but striking molecular assembly for proteins with a Tob/BTG fold, make key advances in understanding the mechanism of sperm fate specification and highlight the potential for undiscovered protein polymers in biology.

developmental biology↗