Biology subjects

Kong, J. H.

Publications and source records attributed to Kong, J. H..

5 recordsLinked to original sources

bioRxiv2025

Design principles of a membrane-spanning ubiquitin ligase

Receptor-type E3 ubiquitin ligases are membrane-spanning assemblies that enable extracellular signals to directly control ubiquitylation in the cytoplasm. Despite playing widespread roles in tissue patterning and homeostasis, metabolism, and immunity, their structures and mechanisms remain poorly understood. Using cryo-electron microscopy, integrated with biophysical and functional studies, we visualized an E3 complex composed of two transmembrane proteins, MEGF8 and MOSMO, and the intracellular RING-family protein MGRN1. This MEGF8-MOSMO-MGRN1 (MMM) complex regulates left-right patterning of the body axis and the development of multiple organs, partly by attenuating signaling through the Hedgehog pathway. We find that the MMM complex functions like a fishing pole: a long, flexible helix attached to a membrane platform suspends an activated and precisely oriented RING domain--like a fishhook--to ubiquitylate the cytoplasmic surfaces of target receptors. Our structure explains how mutations in MEGF8 cause multi-organ birth defects in humans and defines a paradigm for receptor regulation by ubiquitylation.

biochemistry↗

bioRxiv2025

The E3 ubiquitin ligase MGRN1 targets melanocortin receptors MC1R and MC4R via interactions with transmembrane adapters

E3 ubiquitin ligases play a crucial role in modulating receptor stability and signaling at the cell surface, yet the mechanisms governing their substrate specificity remain incompletely understood. Mahogunin Ring Finger 1 (MGRN1) is a membrane-tethered E3 ligase that fine-tunes signaling sensitivity by targeting surface receptors for ubiquitination and degradation. Unlike cytosolic E3 ligases, membrane-tethered E3s require transmembrane adapters to selectively recognize and regulate surface receptors, yet few such ligases have been studied in detail. While MGRN1 is known to regulate the receptor Smoothened (SMO) within the Hedgehog pathway through its interaction with the transmembrane adapter Multiple Epidermal Growth Factor-like 8 (MEGF8), the broader scope of its regulatory network has been speculative. Here, we identify Attractin (ATRN) and Attractin-like 1 (ATRNL1) as additional transmembrane adapters that recruit MGRN1 and regulate cell surface receptor turnover. Through co-immunoprecipitation, we show that ATRN and ATRNL1 likely interact with the RING domain of MGRN1. Functional assays reveal that MGRN1 requires these transmembrane adapters to ubiquitinate and degrade the melanocortin receptors MC1R and MC4R, in a process analogous to its regulation of SMO. Loss of MGRN1 leads to increased surface and ciliary localization of MC4R in fibroblasts and elevated MC1R levels in melanocytes, with the latter resulting in enhanced eumelanin production. These findings expand the repertoire of MGRN1-regulated receptors and provide new insight into a shared mechanism by which membrane-tethered E3 ligases utilize transmembrane adapters to dictate substrate receptor specificity. By elucidating how MGRN1 selectively engages with surface receptors, this work establishes a broader framework for understanding how this unique class of E3 ligases fine-tunes receptor homeostasis and signaling output.

cell biology↗

bioRxiv2020

A ubiquitin-based mechanism for the oligogenic inheritance of heterotaxy and heart defects

The etiology of congenital heart defects (CHDs), amongst the most common human birth defects, is poorly understood partly because of its complex genetic architecture. Here we show that two genes previously implicated in CHDs, Megf8 and Mgrn1, interact genetically and biochemically to regulate the strength of Hedgehog signaling in target cells. MEGF8, a single-pass transmembrane protein, and MGRN1, a RING superfamily E3 ligase, assemble to form a transmembrane ubiquitin ligase complex that catalyzes the ubiquitination and degradation of the Hedgehog pathway transducer Smoothened. Homozygous Megf8 and Mgrn1 mutations increased Smoothened abundance and elevated sensitivity to Hedgehog ligands. While mice heterozygous for loss-of-function Megf8 or Mgrn1 mutations were normal, double heterozygous embryos exhibited an incompletely penetrant syndrome of CHDs with heterotaxy. Thus, genetic interactions between components of a receptor-like ubiquitin ligase complex that tunes morphogen signaling strength can cause a birth defect syndrome inherited in an oligogenic pattern.

developmental biology↗

bioRxiv2019

Sphingomyelin suppresses Hedgehog signaling by restricting cholesterol accessibility at the ciliary membrane

Transmission of the Hedgehog signal across the plasma membrane by Smoothened is proposed to be triggered by its direct interaction with cholesterol. But how is cholesterol, an abundant lipid, regulated tightly enough to control a signaling system that can cause birth defects and cancer? Using toxin-based sensors that distinguish between distinct pools of cholesterol, we find here that Smoothened activation and Hedgehog signaling are driven by a biochemically defined fraction of membrane cholesterol, termed accessible cholesterol. Increasing accessible cholesterol levels by depletion of sphingomyelin, which sequesters cholesterol in complexes, potentiates Hedgehog signaling. By inactivating the transporter-like protein Patched 1, Hedgehog ligands trigger an increase in cholesterol accessibility in the ciliary membrane, the subcellular location for Smoothened signaling. Thus, compartmentalization of Hedgehog signaling in the primary cilium may allow cholesterol accessibility to be used as a second messenger to mediate the communication between Patched 1 and Smoothened, without causing collateral effects on other cellular processes.

cell biology↗

bioRxiv2017

Olig2 and Hes regulatory dynamics during motor neuron differentiation revealed by single cell transcriptomics

During tissue development, multipotent progenitors differentiate into specific cell types in characteristic spatial and temporal patterns. We address the mechanism linking progenitor identity and differentiation rate in the neural tube, where motor neuron (MN) progenitors differentiate more rapidly than other progenitors. Using single cell transcriptomics, we define the transcriptional changes associated with the transition of neural progenitors into MNs. Reconstruction of gene expression dynamics from these data indicate a pivotal role for the MN determinant Olig2 just prior to MN differentiation. Olig2 represses expression of the Notch signaling pathway effectors Hes1 and Hes5. Olig2 repression of Hes5 appears to be direct, via a conserved regulatory element within the Hes5 locus that restricts expression from MN progenitors. These findings reveal a tight coupling between the regulatory networks that control patterning and neuronal differentiation, and demonstrate how Olig2 acts as the developmental pacemaker coordinating the spatial and temporal pattern of MN generation.

developmental biology↗