Biology subjects

Balakrishnan, K.

Publications and source records attributed to Balakrishnan, K..

7 recordsLinked to original sources

bioRxiv2026

Nuclear Cathepsin L Remodels the Replication Machinery to Create a Therapeutic Vulnerability in Ovarian Cancer

Abstract Therapeutic resistance in ovarian cancer is frequently driven by persistent replication stress, yet the molecular mechanisms that convert replication stress into a therapeutically exploitable vulnerability remain incompletely understood. Here, we identify drug-induced nuclear cathepsin L (nCTSL) as a previously unrecognized regulator of replication stress and DNA repair. Clofarabine (CLF) combined with the ATR inhibitor AZD6738, or the CHK1 inhibitor prexasertib promoted nuclear accumulation of CTSL, where it remodeled the replication machinery through degradation of CCNE1, MCM3, MCM6, and geminin, accompanied by loss of RAD51 and 53BP1 and increased {gamma}H2AX and phospho-RPA2. DNA fiber analysis demonstrated marked inhibition of replication fork progression following CLF-based combinations, whereas CTSL depletion accelerated fork progression and abolished therapy-induced replication stress. Reconstitution with the nuclear M1F CTSL isoform restored replication restraint, confirming a direct role for nuclear CTSL in regulating replication dynamics. GFP-based DNA repair reporter assays further revealed that CLF-based combinations suppress DNA repair competence in a CTSL-dependent manner, indicating that nuclear CTSL couples replication stress amplification with functional inhibition of repair pathways. Functionally, CLF-based combinations selectively targeted transformed fallopian tube secretory epithelial cells while sparing non-transformed counterparts, demonstrated broad activity in patient-derived ovarian cancer ascites spheroids, and significantly inhibited tumor growth and prolonged survival in vivo. Collectively, our findings identify nuclear CTSL as a mechanistic driver of replication stress that remodels the replication machinery, impairs DNA repair, and creates a therapeutically exploitable vulnerability in ovarian cancer. We propose that nuclear CTSL promotes a transition from replication competence to replication catastrophe, thereby establishing a conceptual framework for biomarker-guided therapeutic strategies targeting CTSL-dependent replication stress.

cancer biology↗

bioRxiv2025

Genetic insights into Iron Age Saka culture: Ancient DNA analysis of the Boz-Barmak burial ground, Kyrgyzstan

The nomadic cultures of the Iron Age played an important role in shaping the genetic and cultural landscape of Eurasian populations. Yet despite its key geographical location, the Central Eurasian region remains underrepresented in ancient DNA studies of humans. We address this gap through genomic analysis of 12 individuals from the Boz-Barmak burial site in Kyrgyzstan associated with Saka pastoralists (4th-2nd centuries BCE), 9 of which yielded low-coverage genomes. Genetic clustering analysis placed these individuals within the genetic variation of ancient and modern Central Eurasian and Siberian populations. We found no evidence of first-degree relatives in a kinship analysis, however a network of second- and third-degree relationships seems to be present. Notably, all male individuals share the same Y-chromosomal haplotype, common in present-day Kyrgyz and Tajik groups, while mitochondrial DNA showed comparably high diversity, with distinct haplogroups observed across the analysed individuals. These findings are in line with archaeological and ethnographic evidence of patrilocality in Early Iron Age Saka, where male lineages remained stable across generations, while female mobility contributed to genetic diversity. Our study complements our understanding of the interplay between kinship, social organization and population history in nomadic cultures.

genomics↗

bioRxiv2025

Oviposition behavior, nymphal development, and below-ground olfactory preference of Pentastiridius leporinus on twelve Beta vulgaris genotypes

The planthopper Pentastiridius leporinus (Hemiptera: Cixiidae) is the primary vector of two phloem-restricted prokaryotes, which can cause the disease syndrome de basses richesses (SBR) in sugar beet (Beta vulgaris L.). Heavy infestations of this insect have contributed to significant yield losses in Central Europe, but little is known about how different B. vulgaris genotypes influence vector behavior and performance. Understanding such interactions is critical for both pest management and the development of sugar beet cultivars that are less favorable to the vector. We investigated oviposition decisions, nymphal development, and belowground chemotaxis of P. leporinus using twelve B. vulgaris genotypes: eight sugar beet genotypes with contrasting SBR tolerance, two Swiss chard, and two beetroot varieties. In no-choice assays, females oviposited at similar rates on all tested genotypes, indicating broad host suitability. However, in three-choice tests, significant differences emerged, with several genotypes receiving more egg batches than the reference variety Vasco. Despite adult host preferences, nymphal survival, growth, and instar development did not differ among genotypes. In contrast, belowground olfactometer assays revealed that nymphs exhibited clear chemotactic responses: several genotypes attracted significantly more individuals than others. This represents the first documentation of chemotactic host location in P. leporinus nymphs. Our findings reveal a mismatch between adult oviposition preference and nymphal performance, a pattern not uncommon in other generalist herbivores. Both adult and nymphal behaviors were nevertheless influenced by genotype-specific traits, likely linked to plant chemistry. Identifying these cues could inform breeding strategies aimed at reducing vector attraction, thereby complementing pathogen-targeted approaches and supporting integrated management of SBR in sugar beet.

ecology↗

bioRxiv2025

Inhibition of coronaviral exonuclease activity by TRIM-mediated SUMOylation

Members of the TRIM E3 ligase family are effectors of the host innate or intrinsic defense against various viruses; however, how specific TRIM proteins antagonize coronavirus infection is still largely elusive. Through an RNAi screen targeting 71 human TRIM genes, we identified multiple TRIM proteins with antiviral or proviral activity against SARS-CoV-2. TRIM32 potently restricted SARS-CoV-2 replication in a RING E3 ligase-dependent but interferon-independent manner. Mechanistically, TRIM32 binds to and SUMOylates the 3'-to-5' exoribonuclease (ExoN) of NSP14, which is essential for SARS-CoV-2 replication. TRIM32-mediated NSP14 SUMOylation at K9 and K200 inhibits RNA binding and NSP10 cofactor recruitment, respectively, ultimately suppressing ExoN activity. Our study further revealed that NSP14 SUMOylation by TRIM32 and its antiviral activity are broadly conserved for coronaviruses. These results identify the coronaviral NSP14 protein as a direct target of host restriction via SUMOylation, which may uncover novel ways to therapeutically inhibit coronavirus infections in humans.

microbiology↗

bioRxiv2022

A real-time cellular thermal shift assay (RT-CETSA) to monitor target engagement

Determining a molecules mechanism of action is paramount during chemical probe development and drug discovery. The cellular thermal shift assay (CETSA) is a valuable tool to confirm target engagement in cells for a small molecule that demonstrates a pharmacological effect. CETSA directly detects biophysical interactions between ligands and protein targets, which can alter a proteins unfolding and aggregation properties in response to thermal challenge. In traditional CETSA experiments, each temperature requires an individual sample, which restricts throughput and requires substantial optimization. To capture the full aggregation profile of a protein from a single sample, we developed a prototype real-time CETSA (RT-CETSA) platform by coupling a real-time PCR instrument with a CCD camera to detect luminescence. A thermally stable Nanoluciferase variant (ThermLuc) was bioengineered that withstood unfolding at temperatures greater than 90 degrees Celsius and was compatible with monitoring target engagement events when fused to diverse targets. Utilizing well-characterized inhibitors of lactate dehydrogenase alpha, RT-CETSA showed significant correlation with enzymatic, biophysical, and other cell-based assays. A data analysis pipeline was developed to enhance the sensitivity of RT-CETSA to detect on-target binding. The RT-CETSA technology advances capabilities of the CETSA method and facilitates the identification of ligand-target engagement in cells, a critical step in assessing the mechanism of action of a small molecule. SignificanceValidating target engagement is a critical step when characterizing a small molecule modulator. The cellular thermal shift assay (CETSA) is a common approach to examine target engagement, as alterations in the thermal stability of a protein can be conferred by ligand binding. An advantage of CETSA is that it does not require modification of the protein target or small molecule. Major limitations are the throughput and ease-of-use, as the traditional detection method uses western blots, which limits the number of samples that can be processed. Higher-throughput CETSA methods have been developed but are performed at a single temperature and require target-specific optimization. We developed a high-throughput real-time CETSA to circumvent these challenges, providing a rapid and cost-effective strategy to assess on-target activity of a small molecule in living cells.

pharmacology and toxicology↗

bioRxiv2020

Molecular and functional architecture of striatal dopamine release sites

Dopamine controls striatal circuit function, but its transmission mechanisms are not well understood. We recently showed that dopamine secretion requires RIM, suggesting that it occurs at active zone-like sites similar to conventional synapses. Here, we establish using a systematic conditional gene knockout approach that Munc13 and Liprin-, active zone proteins for vesicle priming and release site organization, are important for dopamine secretion. Correspondingly, RIM zinc finger and C2B domains, which bind to Munc13 and Liprin-, respectively, are needed to restore dopamine release in RIM knockout mice. In contrast, and different from conventional synapses, the active zone scaffolds RIM-BP and ELKS, and the RIM domains that bind to them, are expendable. Hence, dopamine release necessitates priming and release site scaffolding by RIM, Munc13, and Liprin-, but other active zone proteins are dispensable. Our work establishes that molecularly simple but efficient release site architecture mediates fast dopamine exocytosis.

neuroscience↗

bioRxiv2020

Loop 1 of APOBEC3C regulates its antiviral activity against HIV-1

APOBEC3 deaminases (A3s) provide mammals with an anti-retroviral barrier by catalyzing dC-to-dU deamination on viral ssDNA. Within primates, A3s have evolved diversely via gene duplications and fusions. Human APOBEC3C (hA3C) efficiently restricts the replication of viral infectivity factor (vif)-deficient Simian immunodeficiency virus (SIV{Delta}vif), but for unknown reasons, it inhibits HIV-1{Delta}vif weakly. In catarrhines (Old World monkeys and apes), the A3C loop 1 displays the conserved amino acid pair WE, while the corresponding consensus sequence in A3F and A3D is the largely divergent pair RK, which is also the inferred ancestral sequence for the last common ancestor of A3C|D|F in primates. Here, we report that modifying the WE residues in hA3C loop 1 to RK leads to stronger interactions with ssDNA substrate, facilitating catalytic function, which resulted in a drastic increase in both deamination activity and the ability to restrict HIV-1 and LINE-1 replication. Conversely, the modification hA3F_WE resulted only in a marginal decrease in HIV-1{Delta}vif inhibition. The two series of ancestral gene duplications that generated A3C, A3D-CTD and A3F-CTD allowed neo/subfunctionalization: A3F-CTD maintained the ancestral RK residues in loop 1, while strong evolutionary pressure selected for the RK[->]WE modification in catarrhines A3C, possibly allowing for novel substrate specificity and function. AUTHOR SUMMARYThe restriction factors of the APOBEC3 (A3) family of cytidine deaminases inhibit the replication of Vif-deficient retroviruses mainly by mutating their viral genomes. While there are seven A3 proteins (A3A-A3H) found in humans only A3G and A3F potently inhibit HIV-1 replication. A3C in general and its retroviral restriction capacity have not been widely studied probably due to its weak anti-HIV-1 activity, however, it displays a strong antiviral effect against SIV. Understanding the role of A3C is important because it is highly expressed in CD4+ T cells, is upregulated upon HIV-1 infection, and is distributed cell-wide. In this study, we report that replacing two residues in loop 1 of A3C protein with conserved positively-charged amino acids enhance the substrate DNA binding, which markedly facilitates its deamination-dependent antiviral activity against HIV-1 as well as increasing the restriction of LINE-1 retroelements. Furthermore, our evolutionary analysis demonstrates that the pressure that caused the loss of potential loop 1 residues occurred only in A3C but not in primate homologues. Overall, our study highlights the possibility of A3C acting as a super restriction factor, however, this was likely evolutionarily selected against to achieve a balance between anti-viral/anti-LINE-1 activity and genotoxicity.

microbiology↗