Biology subjects

Pandita, T. K.

Publications and source records attributed to Pandita, T. K..

5 recordsLinked to original sources

bioRxiv2025

Huntingtin preserves mitochondrial genome integrity in neurons, which is impaired in Huntingtons disease

Huntingtin (HTT) function is enigmatic, as the native protein plays critical roles in neuronal health, while mutant HTT (mHTT), carrying an expanded polyglutamine stretch, triggers neurotoxicity and contributes to the pathogenesis of Huntingtons disease (HD). We recently found that HTT is part of a nuclear transcription-coupled DNA repair (TCR) complex with DNA repair enzymes including polynucleotide-kinase-3-phosphatase (PNKP). This complex resolves DNA lesions during transcription to maintain genome integrity, while in HD, mHTT impairs the activity of this complex, resulting in accumulation of DNA lesions. Using molecular, cellular biology and computational methods, we find that HTT has a role in assembling a functional DNA repair complex in mitochondria. Together with mitochondrial RNA polymerase and transcription factors, HTT resolves mitochondrial DNA lesions to preserve mitochondrial genome integrity and function. Pathogenic mHTT impairs this activity, resulting in persistent DNA lesions and reduced mitochondrial function in HD. Importantly, restoring activity of this complex in a Drosophila HD model through ectopic HTT or PNKP expression significantly improves mitochondrial genome integrity and ameliorates motor deficits. HIGHLIGHTSO_LIHTT organizes a functional, multifactorial mitochondrial DNA repair complex C_LIO_LIMutant HTT impairs the mitochondrial DNA repair complex causing DNA damage accumulation C_LIO_LIHTT-associated repair complex resolves mitochondrial DNA lesions and DNA integrity C_LIO_LIRestoring repair activity in HD flies rescues mitochondrial DNA integrity and motor defects C_LI

neuroscience↗

bioRxiv2024

Chromatin remodeler BRG1 recruits huntingtin to repair DNA double-strand breaks in neurons

Persistent DNA double-strand breaks (DSBs) are enigmatically implicated in neurodegenerative diseases including Huntingtons disease (HD), the inherited late-onset disorder caused by CAG repeat elongations in Huntingtin (HTT). Here we combine biochemistry, computation and molecular cell biology to unveil a mechanism whereby HTT coordinates a Transcription-Coupled Non-Homologous End-Joining (TC-NHEJ) complex. HTT joins TC-NHEJ proteins PNKP, Ku70/80, and XRCC4 with chromatin remodeler Brahma-related Gene 1 (BRG1) to resolve transcription-associated DSBs in brain. HTT recruitment to DSBs in transcriptionally active gene- rich regions is BRG1-dependent while efficient TC-NHEJ protein recruitment is HTT-dependent. Notably, mHTT compromises TC-NHEJ interactions and repair activity, promoting DSB accumulation in HD tissues. Importantly, HTT or PNKP overexpression restores TC-NHEJ in a Drosophila HD model dramatically improving genome integrity, motor defects, and lifespan. Collective results uncover HTT stimulation of DSB repair by organizing a TC-NHEJ complex that is impaired by mHTT thereby implicating dysregulation of transcription-coupled DSB repair in mHTT pathophysiology. Highlights* BRG1 recruits HTT and NHEJ components to transcriptionally active DSBs. * HTT joins BRG1 and PNKP to efficiently repair transcription related DSBs in brain. * Mutant HTT impairs the functional integrity of TC-NHEJ complex for DSB repair. * HTT expression improves DSB repair, genome integrity and phenotypes in HD flies.

neuroscience↗

bioRxiv2021

Caspase-2 regulates S-phase cell cycle events to protect from DNA damage accumulation independent of apoptosis

In addition to its classical role in apoptosis, accumulating evidence suggests that caspase-2 has non-apoptotic functions, including regulation of cell division. Loss of caspase-2 is known to increase proliferation rates but how caspase-2 is regulating this process is currently unclear. We show that caspase-2 is activated in dividing cells in G1- and early S-phase. In the absence of caspase-2, cells exhibit numerous S-phase defects including delayed exit from S-phase, S-phase-associated chromosomal aberrations, and increased DNA damage following S-phase arrest. In addition, caspase-2-deficient cells have a higher frequency of stalled replication forks, decreased DNA fiber length, and impeded progression of DNA replication tracts. This indicates that caspase-2 reduces replication stress and promotes replication fork protection to maintain genomic stability. These functions are independent of the pro-apoptotic function of caspase-2 because blocking caspase-2-induced cell death had no effect on cell division or DNA damage-induced cell cycle arrest. Thus, our data supports a model where caspase-2 regulates cell cycle events to protect from the accumulation of DNA damage independently of its pro-apoptotic function.

cell biology↗

bioRxiv2019

Role of HP1β during spermatogenesis and DNA replication

Maintaining genomic stability in a continually dividing cell population requires accurate DNA repair, especially in male germ cells. Repair and replication protein access to DNA, however, is complicated by chromatin compaction. The HP1{beta} chromatin protein, encoded by Cbx1, is associated with chromatin condensation but its role in meiosis is not clear. To investigate the role of Cbx1 in male germ cells, we generated testis specific Cbx1 deficient transgenic mice by crossing Cbx1flox/flox (Cbx1f/f) mice with Stra8 Cre+/- mice. Loss of Cbx1 in testes adversely affected sperm maturation and Cbx1 deletion increased seminiferous tubule degeneration and basal level DNA damage., We observed that Cbx1-/- MEF cells displayed reduced resolution of stalled DNA replication forks as well as decreased fork restart, indicating defective DNA synthesis. Taken together, these results suggest that loss of Cbx1 in growing cells leads to DNA replication defects and associated DNA damage that impact cell survival.

cell biology↗

bioRxiv2016

DNA damage response decreases during induced pluripotent and embryonic stem cell differentiation

Genomic integrity is critical for preservation of stem cell function and is, maintained through a robust DNA damage response (DDR) with systemized DNA DSB repair by either the non-homologous end joining (NHEJ) pathway or the homologous recombination (HR) pathway. To examine DDR during stem cell differentiation, human embryonic (hES) and induced pluripotent stem (IPS) cells were exposed to DNA damaging agents and DNA damage signaling/repair measured. Differentiated cells displayed a higher frequency of residual DNA damage, chromosomal aberrations, cells with delayed {gamma}-H2AX foci disappearance and a reduced number of RAD51 foci. Factors impacting DNA DSB repair by HR formed reduced foci in differentiated cells. The reduction in repairosome foci formation after DNA damage was not due to changes in HR protein levels, which were unchanged by differentiation. Differentiated cells also displayed a higher frequency of stalled DNA replication forks and decreased firing of new replication origins from transient inhibition of DNA synthesis by hydroxyurea treatment. In addition, we observed that differentiated cells exhibit a higher frequency of R-loops. A similar decline in DDR was observed as early stage mouse astrocytes differentiated into later stage astrocytes. Our studies thus suggest that DSB repair by homologous recombination is increasingly impaired during stem cell differentiation while the NHEJ pathway is minimally altered.

cell biology↗