Biology subjects

Kron, S. J.

Publications and source records attributed to Kron, S. J..

4 recordsLinked to original sources

bioRxiv2025

N-Terminal Deleted Isoforms of E3 Ligase RNF220 (Isoform 4) Are Ubiquitously Expressed and Required for Mouse Muscle Differentiation.

Four isoform peptides of the novel E3 ligase RNF220 have been identified in humans. However, all of previous studies have predominantly focused on isoform 1, which consists of 566 amino acids (aa). Here, we show that a shorter isoform, isoform 4 (308 aa), lacking most of the N-terminus, is the predominant and ubiquitously expressed variant that warrants functional investigation. Both isoform 1 and isoform 4 are expressed in the brain; however, isoform 4 is the major isoform expressed in all other tissues in mice. Consistently, H3K4me3 ChIP-seq data from ENCODE reveal that the transcription start site for isoform 4 demonstrates broader and stronger activity across human tissues than that of isoform 1. Isoform 4 produces two peptides (4a and 4b) through alternative translation initiation, with isoform 4b displaying distinct subcellular localization and subnuclear structures. Notably, during embryonic stem cell differentiation into neural stem cells, isoform 1 expression increases, whereas isoform 4 expression decreases. In murine myoblasts, isoform 4 is the sole expressed isoform and is required for MyoD and myogenin expression, as well as for muscle differentiation. Our findings highlight isoform 4 as the ubiquitously and highly expressed variant, likely playing a fundamental role across tissues while exhibiting functional differences from isoform 1. These results emphasize the critical importance of isoform 4 in future studies investigating the biological functions of RNF220.

molecular biology↗

bioRxiv2024

Timing anti-PD-L1 checkpoint blockade immunotherapy to enhance tumor irradiation

BackgroundThe ability of radiotherapy (RT) to drive anti-tumor immunity is limited by adaptive resistance. While RT induces inflammation and recruits activated tumor-infiltrating lymphocytes (TILs) including cytotoxic T lymphocytes (CTLs), the resulting radiation- and IFN{gamma}-dependent PD-L1 expression restores an immunosuppressed tumor microenvironment. Unleashing an effective anti-tumor response may require precise sequencing of RT and checkpoint blockade immunotherapy (CBI) to block PD-L1 signaling before it can mediate its suppressive effects. MethodsFlank tumors formed in BALB/c mice with syngeneic CT26 colon or 4T1 mammary carcinoma cells were treated with otherwise ineffective doses of ionizing radiation (10 Gy) followed by CBI (0.2 mg anti-PD-L1, i.v.) after 0, 1, 3, 5 or 7 days, comparing tumor response. Anti-PD-L1 delivery was measured by fluorescence, TILs by flow cytometry and immunofluorescence, PD-L1 expression by immunohistochemistry, and tumor size by calipers. Results In both CT26 and 4T1 tumors, 10 Gy alone resulted in a transient growth delay associated with infiltrating CTLs peaking at 3 days and PD-L1 at 5 days. CTLs returned toward baseline by 7 days, consistent with adaptive resistance. Anti-PD-L1 failed to potentiate radiation except when injected 5 days after 10 Gy, which prevented CTL depletion and led to tumor elimination. Potentially contributing to compound effects, anti-PD-L1 penetrated tumors and bound PD-L1 more efficiently after irradiation. ConclusionsOptimal timing to exploit radiation-induced permeability to enhance CBI delivery and interrupt adaptive resistance by blocking PD-L1 as it peaks may offer a general strategy to enhance external beam radiotherapy by protecting activated TILs and potentiating anti-tumor immune response.

cancer biology↗

bioRxiv2021

Global Epigenetic Analysis Reveals H3K27 Methylation as a Mediator of Double Strand Break Repair

The majority of cancer patients is treated with ionizing radiation (IR), a relatively safe and effective treatment considered to target tumors by inducing DNA double strand breaks (DSBs). Despite clinical interest in increasing the efficacy of IR by preventing successful DSB repair, few effective radio-adjuvant therapies exist. Extensive literature suggests that chromatin modifiers play a role in the DSB repair and thus may represent a novel class of radiosensitizers. Indeed, chromatin has both local and global impacts on DSB formation, recognition of breaks, checkpoint signaling, recruitment of repair factors, and timely DSB resolution, suggesting that epigenetic deregulation in cancer may impact the efficacy of radiotherapy. Here, using tandem mass spectrometry proteomics to analyze global patterns of histone modification in MCF7 breast cancer cells following IR exposure, we find significant and long-lasting changes to the epigenome. Our results confirm that H3K27 trimethylation (H3K27me3), best known for mediating gene repression and regulating cell fate, increases after IR. H3K27me3 changes rapidly, accumulating at sites of DNA damage. Inhibitors of the Polycomb related complex subunit and H3K27 methyltransferase EZH2 confirm that H3K27me3 is necessary for DNA damage recognition and cell survival after IR. These studies provide an argument for evaluating EZH2 as a radiosensitization target and H3K27me3 as a marker for radiation response in cancer. Proteomic data are available via ProteomeXchange with identifier PXD019388.

cancer biology↗

bioRxiv2020

Subcellular localization of the J-protein Sis1 regulates the heat shock response

Cells exposed to heat shock induce a conserved gene expression program - the heat shock response (HSR) - encoding chaperones like Hsp70 and other protein homeostasis (proteostasis) factors. Heat shock also triggers proteostasis factors to form subcellular quality control bodies, but the relationship between these spatial structures and the HSR is unclear. Here we show that localization of the J-protein Sis1 - a co-chaperone for Hsp70 - controls HSR activation in yeast. Under nonstress conditions, Sis1 is concentrated in the nucleoplasm where it promotes Hsp70 binding to the transcription factor Hsf1, repressing the HSR. Upon heat shock, Sis1 forms an interconnected network with other proteostasis factors that spans the nucleolus and the surface of the cortical ER. We propose that localization of Sis1 to this network directs Hsp70 activity away from Hsf1 in the nucleoplasm, leaving Hsf1 free to induce the HSR. In this manner, Sis1 couples HSR activation to the spatial organization of the proteostasis network. One sentence summaryLocalization of the J-protein Sis1 to a subcellular network of proteostasis factors activates the heat shock response.

cell biology↗