Biology subjects

Gassman, N. R.

Publications and source records attributed to Gassman, N. R..

3 recordsLinked to original sources

bioRxiv2026

Parkinson's disease linked LRRK2 G2019S drives oxidative nuclear DNA damage and PARP1 hyperactive signaling

LRRK2 mutations are the most common cause of autosomal-dominant Parkinsons disease (PD), with G2019S linked to both familial and sporadic PD. Although LRRK2-mediated mitochondrial DNA damage is implicated in PD, the contribution of nuclear DNA damage is less understood. Using CRISPR/Cas9-generated LRRK2G2019S/G2019S knock-in cells, we discovered increased sensitivity to oxidative and alkylating DNA-damaging agents compared to wild-type, consistent with compromised tolerance/repair of lesions processed by base excision repair (BER). The oxRADD assay revealed elevated endogenous oxidative nuclear base damage in LRRK2 mutant cells. Concomitantly, PARP1-dependent poly(ADP-ribose) (PAR) levels were markedly increased, with chromatin enrichment of PARP1 and BER factors (XRCC1, DNA ligase III) only in LRRK2G2019S/G2019S cells, indicating BER initiation, without successful resolution. LRRK2G2019S/G2019S cells displayed synthetic lethality with PARP-trapping inhibitors (olaparib) but tolerated PARP1 knockdown, suggesting cytotoxicity from stabilized PARP-DNA complexes rather than loss of catalytic activity. The SOD/catalase mimetic EUK-134 abrogated LRRK2 G2019S-dependent PAR accumulation, whereas the mitochondrial complex I inhibitor rotenone exacerbated PAR levels, linking reactive oxygen species (ROS) to BER dysfunction and PARP1 hyperactivation. Overall, we have identified a ROS-dependent PARP1 hyperactivation pathway that underlies LRRK2 G2019S-associated cellular vulnerability.

cell biology↗

bioRxiv2024

Apurinic/apyrimidinic endodeoxyribonuclease 2 (APEX2/APE2) is required for efficient expression of TERT in human embryonic stem cells.

Human stem cells rely on enhanced DNA repair mechanisms to safeguard their ability to replenish somatic tissues. Telomerase counteracts telomere shortening and is a component of the stem cell DNA repair system that is regulated by ATM and ATR kinases. Here, we report that the DNA repair enzyme APEX2, but not its close paralog APEX1, is required for efficient telomerase reverse transcriptase (TERT) gene expression in human embryonic stem cells (hESC) and a melanoma cell line. We also observed that APEX2 knockdown significantly diminished telomerase enzyme activity. While APEX1 is known to regulate certain transcription factors, APEX2 has not been reported to influence gene expression. To gain insight into how APEX2 influences gene expression, we conducted RNA-seq following APEX2 knockdown in hESC. These results indicated that a number of genes, in addition to TERT, relied on APEX2 for efficient expression. Genes affected by APEX2 knockdown were significantly enriched for specific repetitive DNA families. These include mammalian-wide interspersed repeats (MIRs) and Alu elements. Chromatin immunoprecipitation experiments demonstrated the highest APEX2 binding near MIR sequences in TERT intron 2. Surprisingly, binding was low in the TERT proximal promoter, a region known to control TERT transcription. MIR and other repetitive DNA regions are common sites of DNA damage, suggesting that APEX2 recruitment and repair of TERT MIR sequences may play a role in influencing TERT expression. This new role for APEX2 in promoting efficient gene expression deepens our understanding of an emerging cancer therapeutic target. Further, as the TERT gene plays critical roles in stem cell maintenance, organismal development and aging, as well as in short telomere disorders and cancer, our observations provide insight into new strategies to modulate the expression of this important enzyme.

cell biology↗

bioRxiv2019

Defective base excision repair in the response to DNA damaging agents in triple negative breast cancer

DNA repair defects have been increasingly focused on as therapeutic targets. In hormone positive breast cancer, XRCC1-deficient tumors have been identified and proposed as targets for combination therapies that damage DNA and inhibit DNA repair pathways. XRCC1 is a scaffold protein that functions in base excision repair (BER) by mediating essential interactions between DNA glycosylases, AP endonuclease, poly(ADP-ribose) polymerase 1, DNA polymerase {beta} (POL {beta}), and DNA ligases. Loss of XRCC1 confers BER defects and hypersensitivity to DNA damaging agents. BER defects have not been evaluated in triple negative breast cancer (TNBC), for which new therapeutic targets and therapies are needed. To evaluate the potential of XRCC1 as an indicator of BER defects in TNBC, we examined XRCC1 expression and localization in the TCGA database and in TNBC cell lines. High XRCC1 expression was observed for TNBC tumors in the TCGA database and expression of XRCC1 varied between TNBC cell lines. We also observed changes in XRCC1 subcellular localization in TNBCs that alter the ability to repair base lesions and single-strand breaks. Subcellular localization changes were also observed for POL {beta} that did not correlate with XRCC1 localization. Basal levels of DNA damage were also measured in the TNBC cell lines, and damage levels correlated with observed changes in XRCC1 expression, localization, and repair functions. The results confirmed that XRCC1 expression changes may indicate DNA repair capacity changes but emphasize that basal DNA damage levels along with expression and localization are better indicators of DNA repair defects. Given the observed over-expression of XRCC1 in TNBC preclinical models and the TCGA database, XRCC1 expression levels should be considered when evaluating treatment responses of TNBC preclinical model cells.

cancer biology↗