Biology subjects

Ragupathi, A.

Publications and source records attributed to Ragupathi, A..

3 recordsLinked to original sources

bioRxiv2026

The function of human PIF1 in G quadruplex formation and replication stress response at ALT telomeres

Cancers maintain their telomeres through two telomere maintenance mechanisms: 85-90% of cancers rely on telomerase (TEL+), while 10-15% of cancers adopt the Alternative Lengthening of Telomeres (ALT) pathway. The Break-Induced Replication (BIR) pathway plays a critical role in maintaining telomere length in the ALT+ cells. In both yeast and human, PIF1, a 5' to 3' helicase, is required for the robust activity of BIR. However, the extent of human PIF1 (hPIF1) involvement in the ALT pathway remains unknown. Here we showed that hPIF1 can be recruited to damaged telomeres in ALT+ cells. In addition, we demonstrated that inhibition of hPIF1 induced DNA damage and G quadruplex (G4) accumulation at ALT telomeres, leading to a moderate reduction of the mean telomere length. Most interestingly, we demonstrated that inhibition of hPIF1 also attenuates checkpoint activation, BLM recruitment, single-stranded DNA (ssDNA) formation, DNA damage, and G4s at telomeres in the FANCM deficient ALT+ cells. Finally, we showed that inactivation of hPIF1 affects the viability of both ALT+ and TEL+ cancers, suggesting that hPIF1 is a potential drug target for cancer therapy.

molecular biology↗

bioRxiv2025

DNA2 and FANCM function in two distinctive pathways in disrupting TERRA R-loops and suppressing replication stress at ALT telomeres

Cancers maintain their telomeres through two main telomere maintenance mechanisms (TMMs): 85-90% of cancers rely on telomerase, while 10-15% of cancers adopt the Alternative Lengthening of Telomere (ALT) pathway. Previously, we and others reported that FANCM, one of the Fanconi Anemia proteins, plays a critical role in suppressing replication stress and DNA damage at ALT telomeres by actively disrupting TERRA R-loops [1-4]. Here, we showed that inactivation of DNA2 in ALT-positive (ALT+) cells, but not in telomerase-positive (TEL+) cells, induces a robust increase of replication stress and DNA damage at telomeres, which leads to a pronounced increase of many ALT properties, including telomere dysfunction-induced foci (TIFs), ALT-associated PML bodies (APBs), and C-circles. We further demonstrated that depletion of DNA2 induces a pronounced increase of TERRA R-loops and a decrease in replication efficiency at ALT telomeres. Most importantly, we uncovered a strong additive genetic interaction between DNA2 and FANCM in the ALT pathway. Furthermore, co-depletion of DNA2 and FANCM causes synthetic lethality in ALT+ cells, but not in TEL+ cells, suggesting that targeting DNA2 and FANCM could be a viable strategy to treat ALT+ cancers. Finally, utilizing the single-molecule telomere assay via optical mapping (SMTA-OM) technology, we thoroughly characterized genome-wide changes in DNA2 deficient cells and FANCM deficient cells and found that most chromosome arms manifested increased telomere length. Unexpectedly, we uncovered many chromosome arm-specific telomere changes in those cells, suggesting that telomeres at different chromosome arms may regulate and respond to replication stress differently. Collectively, our study not only shed new light on the molecular mechanisms of the ALT pathway, but also discovered a new strategy for targeting ALT+ cancer.

cancer biology↗

bioRxiv2021

Caveolin-1 temporal modulation enhances trastuzumab and trastuzumab-drug conjugate efficacy in heterogeneous gastric cancer

Resistance mechanisms and heterogeneity in HER2-positive gastric cancers (GC) limit trastuzumab benefit in 32% of patients, and other targeted therapies have failed in clinical trials. Using genomic data from patient tissue, patient-derived xenografts (PDXs), partially humanized biological models, and HER2-targeted imaging we identified caveolin-1 (CAV1) as a complementary biomarker in GC selection for trastuzumab therapy. In retrospective analyses of samples from patients enrolled on trastuzumab trials, the CAV1-high profile was associated with low membrane HER2 density and reduced patient survival. We found a negative correlation between CAV1 tumoral protein levels - a major protein of cholesterol-rich membrane domains - and trastuzumab-drug conjugate TDM1 tumor uptake. Finally, CAV1 depletion using knockdown or pharmacologic approaches was shown to increase HER2-directed immunoPET uptake and TDM1 efficacy in GC with incomplete HER2 membranous reactivity. In support of these findings, background statin use in patients is associated with enhanced antibody efficacy. Together, this work provides mechanistic justification and clinical evidence that require prospective investigation of HER2-targeted therapies combined with statins to delay drug resistance in GC. SIGNIFICANCEThis study identifies how CAV1 protein expression and statin use relate to GC response in HER2-targeted imaging and therapeutic approaches. In addition, to support the synergy of CAV1 depletion with TDM1 observed in mouse models, we demonstrate that statin users had better clinical responses to antibody-based therapies in HER2+ GC.

cancer biology↗