Biology subjects

Gothwal, S. K.

Publications and source records attributed to Gothwal, S. K..

5 recordsLinked to original sources

bioRxiv2026

Reduced B cell activation in Germinal center reaction of the mouse model of Li-Fraumeni syndrome

The TP53 mutation associated with Li-Fraumeni syndrome in humans is known to exhibit p53 gain-of-function properties leading to early cancer onset. To explore whether these patients also have compromised immune responses due to p53 mutations, we investigated the humoral immune response using a Li-Fraumeni mouse model harboring a structural mutation, Trp53R172H (equivalent to codon 175 in humans). Trp53R172H mice were immunized with sheep red blood cells, and the Germinal center response was monitored. Our results revealed that SRBC-immunized Trp53R172H mice exhibit reduced B cell activation during the GC reaction. These suggest a selective role for p53 in promoting B cell activation early in the GC reaction prior to BCL6 upregulation. We propose that impaired B cell activation in Li-Fraumeni patients could contribute to immune deficiencies and heightened susceptibility to autoimmune disorders, potentially influencing the development of secondary cancers and impairing therapeutic responses to chemotherapies and immunotherapies. Key PointsO_LITrp52R172H mice exhibit reduced B cell activation during the Germinal center reaction C_LIO_LIRatio of activated B cells in DZ to LZ remain unchanged in Trp52R172H mice. C_LI

cancer biology↗

bioRxiv2025

Isolation of region-specific factors assembled on the Immunoglobulin heavy chain locus during antibody class switch recombination

Activation-Induced Cytidine Deaminase (AID) induces DNA double-strand breaks (DSBs) at the switch (S) regions of the Immunoglobulin heavy chain (Igh) locus, which are essential for Class Switch Recombination (CSR) and Somatic Hypermutation (SHM), key processes for effective antibody production. While AID activity is critical, its off-target effects, such as DSBs at the Myc locus, can cause chromosomal translocations like Igh-Myc fusions, contributing to B-cell lymphomas. The factors assembled on Igh locus that tether AID-induced DSBs and subsequently the CSR, remain unknown. To address this, we developed a method to isolate CSR-specific factors by inserting a 5X-GAL4-UAS sequence at the switch-mu (S{micro}) region in CH12 cells. This engineered site enables recruitment of a 3-FLAG-GAL4 DNA-binding protein (3F-GAL4-DBD), allowing specific pulldown of proteins enriched at the S{micro} region. Successful recovery of BRD2 from the S{micro} region, a known CSR regulator, validated this approach. Characterizing these factors may uncover novel regulators of CSR and highlight mechanisms that balance antibody diversification with genomic integrity in B cells.

molecular biology↗

bioRxiv2025

DNA replication stress-induced transcriptome of Human Burkitt lymphoma identifies MBD1 as a novel suppressor of BCL6 rearrangements in germinal center derived B-lymphomagenesis

BCL6 is a master transcriptional regulator of germinal center (GC) B cells. BCL6 is frequently translocated at the major translocation cluster (MTC) within intron 1 of the BCL6 locus, a hotspot commonly rearranged in diffuse large B cell lymphomas (DLBCLs). BCL6 amplifications are associated with therapeutic resistance and poor survival outcomes in hematological and solid cancers. However the mechanisms suppressing genome instability at the BCL6-MTC preventing BCL6 rearragements remain unclear. Here, transcriptome analysis and genome-wide mapping of histone H3 lysine 4 trimethylation (H3K4me3) in hydroxyurea (HU)-treated Raji cells (a Burkitts lymphoma model) revealed the induced expression of MBD1, encoding the DNA CpG methylation-binding protein. Functional studies using shRNA silencing and ectopic overexpression demonstrated that MBD1 suppresses BCL6 transcription whose promoter harbours conserved CpG methylation sites, suggesting a DNA methylation-dependent regulation of BCL6 trasncription by MBD1. Conversely, BCL6 repressed MBD1 expression by binding to its promoter. MBD1-depleted Raji cells exhibited increased genomic instability at the BCL6-MTC upon HU treatment, heightened sensitivity to DNA replication inhibitors (HU, gemcitabine, and etoposide), and reduced tumorigenicity in xenograft mouse models. We propose that MBD1 prevents genomic instability at the BCL6-MTC to suppress DLBCL formation. Moreover, MBD1 promotes genomic stability and cell viability during DNA replication stress. MBD1 thus represents a potential therapeutic target for cancers exhibiting resistance to chemotherapies targeting DNA replication. Key PointsO_LIMBD1 suppresses BCL6 expression under the DNA replication stress C_LIO_LIMBD1 suppresses genomic instability at BCL6 translocation hotspots C_LIO_LIMBD1 depletion is associated with reduced tumorigenicity in mouse xenograft and sensitivity to DNA replication inhibitors. C_LI

cancer biology↗

bioRxiv2024

Stress Induced Signaling Pathways in Burkitt Lymphoma Play Novel Mechanisms in Fate Determination and Pathogenesis of Germinal Center-Derived B-Lymphomas

B cell receptor signaling, NF-{kappa}B signaling, BCL6 and p53 regulation are essential for germinal center (GC) B cell fate. Dysregulation of these pathways drives the pathogenesis and treatment resistance of GC-derived B-lymphomas (GCDBL). To explore how these pathways affect GCDBL fate and pathogenesis, we treated Raji cells (a GCDBL and Burkitts lymphoma) with mild hydroxyurea (HU) to simulate genotoxic stress encountered by GC B cells. Genome-wide mapping of histone H3K4me3 and p53 target analysis in HU-treated Raji cells combined with transcriptome analysis of human tonsil GC B cells identified ATAD2B (a p53 target) as differentially expressed. We found that p53 suppresses ATAD2B and ATAD2, while ATAD2 and BCL6 transcripts positively correlate in DLBCLs, suggesting that p53 regulates BCL6 in GC B cells via ATAD2 suppression. We propose that p53 regulation of BCL6 quality assures GC B cells before GC exit. Unlike BCL6 suppression of IFN-{gamma} and NF-{kappa}B signaling in GC B cells, we identified IFNGR1 as a loosely bound BCL6 target and observed loss of BCL6 regulation on genes encoding inhibitory subunits of NF-{kappa}B signaling in B-lymphoma treated with a Bruton tyrosine kinase (BTK) inhibitor. These adaptations, alongside with prevalent genetic inactivation of NF-{kappa}B inhibitory genes in DLBLCs, likely contribute to DLBCL pathogenesis and therapy resistance. Our findings highlight the pivotal role of the p53-BCL6 axis in GC B cell fate and its dysregulation in DLBCL pathogenesis and chemoresistance. Key HighlightsO_LIGenes induced in human Burkitts lymphoma under genotoxic stress are largely independent of histone H3K4me3 marks at transcriptional start sites (TSS). C_LIO_LILoss of BCL6 regulation on genes encoding components of IFN-{gamma} signaling is associated with reduced survival and the pathogenesis of DLBCL. C_LIO_LIInactivating mutations in genes encoding components of the NF-{kappa}B inhibitory subunit serve as an adaptation for DLBCL pathogenesis. C_LIO_LIBCL6 expression is correlated with ATAD2 overexpression in DLBCL and solid tumors. C_LI

cancer biology↗

bioRxiv2024

Distal super-enhancer drives aberrant CXCL13 in Cancer cells driving growth and p53 dysregulation via CXCR5-CXCL13 axis

The CXCL13 chemokine plays a crucial role in guiding B cell migration to the light zones (LZs) during the germinal center (GC) reaction. While CXCL13 expression is absent in most cell types, aberrant amplification of the CXCR5-CXCL13 signaling is observed in various cancers, including germinal center-derived B-lymphomas (GCDBL), colorectal adenocarcinoma (COAD), and liver hepatocellular carcinoma (LIHC). However, the molecular mechanisms underlying abnormal CXCL13 transcription in cancer cells and its functional consequences remain elusive. We identify DNA-CpG methylation binding protein 1 (MBD1) as a suppressor of CXCL13 expression. Chromosomal conformation capture (3C) analysis reveals a distal super-enhancer located near CCNG2 that interacts with the CXCL13 promoter in GCDBL, suggesting that enhancer-hijacking drives the aberrant expression. Our functional validation demonstrates that CXCR5-CXCL13 signaling suppresses p53 and its target genes in GCDBLs, COAD, and LIHC. Notably, CXCL13 in the GCDBL cell line Raji disrupts CXCR5-mediated migration, a mechanism essential for (light zone) LZ-entry and affinity maturation of GC B cells. These findings highlight the dual role of the CXCR5-CXCL13 axis in immune response and cancer proliferation. Key PointsO_LISuper-enhancer near CCNG2 region interacts with CXCL13-TSS driving CXCL13 in cancers. C_LIO_LIAberrant CXCL13 prevents CXCR5-mediated migration of B-lymphomas and promotes growth and p53 dysregulation in CXCR5+ cells C_LIO_LICXCR5-CXCL13 axis impairs p53 target gene expression and promotes tumor growth C_LI O_FIG O_LINKSMALLFIG WIDTH=171 HEIGHT=200 SRC="FIGDIR/small/609994v2_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@abf94corg.highwire.dtl.DTLVardef@7bfd55org.highwire.dtl.DTLVardef@351645org.highwire.dtl.DTLVardef@1493e62_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIAberrant CXCL13 expression in hematological and solid cancers C_LIO_LIChemotherapeutic treatment of cancer cells promotes CXCL13 and CXCR5 expression C_LIO_LIDistal super-enhancer on CCNG2 interacts with CXCL13 promoter C_LIO_LICXCL13 expression in B-lymphomas prevents CXCR5-dependent migration C_LIO_LICXCR5-CXCL13 axis encounters p53 function in hematological and solid cancer cells C_LI

cancer biology↗