Biology subjects

Khanchandani, V.

Publications and source records attributed to Khanchandani, V..

5 recordsLinked to original sources

bioRxiv2026

HOT1 functions as a homodimer to promote ALT-permissive chromatin

Telomere homeostasis is a tightly regulated and dynamic process sustained by a network of proteins that organize telomeric chromatin and safeguard chromosome stability. In ALT-positive cells, telomere maintenance relies on recombination-based mechanisms and is modulated by local chromatin states and epigenetic regulation. Here, we show that the telomeric binding protein HOT1 (HMBOX1) requires dimerization - depending both on interaction with the dimerization-mediators DYNLL1/2 and its intrinsic HNFp1 domain - for its stable association with telomeres in vivo. Loss of HOT1 leads to an epigenetic switch from H3K9acK14ac to H3K9me3 at telomeres accompanied by attenuated ALT activity as illustrated by reduced ALT recombination by-products (C-circles) and a decrease in telomere dysfunction-induced foci (TIFs). We further show via binding assays and cross-linking mass spectrometry (XL-MS) analyses that HOT1 directly interacts with telomeric nucleosomes, providing a molecular basis for its involvement in telomeric chromatin organization. Collectively, these findings suggest that HOT1 functions as a homodimer to promote a telomeric chromatin state that is highly permissive for ALT recombination.

cell biology↗

bioRxiv2025

A Chk1-Sp1-CD59 axis of the DNA damage response impedes rituximab-mediated complement-dependent cytotoxicity

The DNA damage response (DDR) is a central regulator of cancer cell fate, coordinating both pro-death and pro-survival pathways in response to genotoxic stress. Here, we reveal an unexpected role for the DDR at the cell surface, in mediating immune evasion from complement-dependent cytotoxicity (CDC), an innate immune mechanism exploited by therapeutic monoclonal antibodies (mAbs). In the context of diffuse large B-cell lymphoma (DLBCL), where the anti-CD20 mAb rituximab utilizes CDC, we show that genotoxic chemotherapy induces expression of membrane-bound complement regulatory proteins (mCRPs) CD46, CD55, and CD59, thereby reducing CDC sensitivity and compromising rituximab activity. In this setting, CD59 emerged as the dominant DDR-induced inhibitor of complement-mediated killing. A high-throughput kinase inhibitor screen identified checkpoint kinase 1 (Chk1) as a critical mediator of this response. Mechanistically, DNA damage activates Chk1, enhancing CD59 transcription via an Sp1-bound promoter. Co-immunoprecipitation mass spectrometry revealed a Chk1 dependent remodelling of Sp1-associated complexes to a transcriptionally active state with recruitment of the histone acetyltransferase KAT2A. These findings expand the role of the DDR in immune resistance at the tumor cell surface, and highlight a negative interaction between chemotherapy and monoclonal antibodies that may require sequential administration or targeting of the Chk1- Sp1-CD59 axis. SignificanceThe DNA Damage Response upregulates complement-protective proteins, extending its role in modulating immune evasion at the cell surface, with direct implications for combinations of chemotherapy and monoclonal antibodies widely used in cancer.

cancer biology↗

bioRxiv2023

ZBTB48 is a pioneer factor regulating B-cell-specific CIITA expression

CIITA is the master regulator of MHC II gene expression and hence the adaptive immune response. CIITA expression itself is tightly regulated by three cell type-specific promoters, pI, pIII, and by pIV, and can also be induced by IFN{gamma} in non-immune cells. While key regulatory elements have been identified within these promoters, knowledge of transcription factors regulating CIITA is incomplete. Here, we demonstrate that the telomere-binding protein and transcriptional activator ZBTB48 directly binds to both the critical activating elements within CIITA pIII and is essential for its gene expression. ZBTB48 establishes open chromatin at CIITA pIII upstream of activating H3K4me3 modifications both priming CIITA transcription for IFN{gamma}-induction and ensuring constitutive expression in primary murine B cells. Hence, ZBTB48 acts as a molecular on-off-switch for B-cell-specific CIITA expression.

immunology↗

bioRxiv2023

ChIP-MS reveals the local chromatin composition by label-free quantitative proteomics

Chromatin immunoprecipitation (ChIP) has been a cornerstone for epigenetic analyses over the last decades, but even coupled to sequencing approaches (ChIP-seq), it is ultimately limited to one protein at a time. In a complementary effort, we here combined ChIP with label-free quantitative (LFQ) mass spectrometry (ChIP-MS) to interrogate local chromatin compositions. We demonstrate the versatility of our approach at telomeres, with transcription factors, in tissue and by dCas9-driven locus-specific enrichment.

biochemistry↗

bioRxiv2022

ZNF524 directly interacts with telomeric DNA and supports telomere integrity

Telomeres are nucleoprotein structures at the ends of linear chromosomes. In humans, they consist of TTAGGG repeats, which are bound by dedicated proteins such as the shelterin complex. This complex blocks unwanted DNA damage repair at telomeres, e.g. by suppressing non-homologous end joining (NHEJ) through its subunit TRF2. We here describe ZNF524, a zinc finger protein that directly binds telomeric repeats with nanomolar affinity and reveal the base-specific sequence recognition by co-crystallization with telomeric DNA. ZNF524 localizes to telomeres and specifically maintains the presence of the TRF2/RAP1 subcomplex at telomeres without affecting other shelterin members. Loss of ZNF524 concomitantly results in an increase in DNA damage signaling and recombination events. Overall, ZNF524 is a direct telomere-binding protein involved in the maintenance of telomere integrity.

cell biology↗