Oncometabolite 2-hydroxyglutarate suppresses basal protein levels of DNA polymerase beta that enhances alkylating agent and PARG inhibition induced cytotoxicity.

Mutations in isocitrate dehydrogenase isoform 1 (IDH1) are primarily found in secondary glioblastoma (GBM) and low-grade glioma but are rare in primary GBM. The standard treatment for GBM includes radiation combined with temozolomide, an alkylating agent. Fortunately, IDH1 mutant gliomas are sensitive to this treatment, resulting in a more favorable prognosis. However, it's estimated that up to 75 % of IDH1 mutant gliomas will progress to WHO grade IV over time and develop resistance to alkylating agents. Therefore, understanding the mechanism(s) by which IDH1 mutant gliomas confer sensitivity to alkylating agents is crucial for developing targeted chemotherapeutic approaches. The base excision repair (BER) pathway is responsible for repairing most base damage induced by alkylating agents. Defects in this pathway can lead to hypersensitivity to these agents due to unresolved DNA damage. The coordinated assembly and disassembly of BER protein complexes are essential for cell survival and for maintaining genomic integrity following alkylating agent exposure. These complexes rely on poly-ADP-ribose formation, an NAD+-dependent post-translational modification synthesized by PARP1 and PARP2 during the BER process. At the lesion site, poly-ADP-ribose facilitates the recruitment of XRCC1. This scaffold protein helps assemble BER proteins like DNA polymerase beta (Polß), a bifunctional DNA polymerase containing both DNA synthesis and 5'-deoxyribose-phosphate lyase (5'dRP lyase) activity. Here, we confirm that IDH1 mutant glioma cells have defective NAD+ metabolism, but still produce sufficient nuclear NAD+ for robust PARP1 activation and BER complex formation in response to DNA damage. However, the overproduction of 2-hydroxyglutarate, an oncometabolite produced by the IDH1 R132H mutant protein, suppresses BER capacity by reducing Polß protein levels. This defines a novel mechanism by which the IDH1 mutation in gliomas confers cellular sensitivity to alkylating agents and to inhibitors of the poly-ADP-ribose glycohydrolase, PARG.

Melanoma-Derived DNA Polymerase Theta Variants Exhibit Altered DNA Polymerase Activity.

DNA polymerase θ (Pol θ or POLQ) is primarily involved in repairing double-stranded breaks in DNA through an alternative pathway known as microhomology-mediated end joining (MMEJ) or theta-mediated end joining (TMEJ). Unlike other DNA repair polymerases, Pol θ is thought to be highly error-prone yet critical for cell survival. We have identified several POLQ gene variants from human melanoma tumors that experience altered DNA polymerase activity, including a propensity for incorrect nucleotide selection and reduced polymerization rates compared to WT Pol θ. Variants are 30-fold less efficient at incorporating a nucleotide during repair and up to 70-fold less accurate at selecting the correct nucleotide opposite a templating base. This suggests that aberrant Pol θ has reduced DNA repair capabilities and may also contribute to increased mutagenesis. Moreover, the variants were identified in established tumors, suggesting that cancer cells may use mutated polymerases to promote metastasis and drug resistance.

Melanoma-derived DNA polymerase theta variants exhibit altered DNA polymerase activity.

DNA Polymerase θ (Pol θ or POLQ) is primarily involved in repairing double-stranded breaks in DNA through the alternative pathway known as microhomology-mediated end joining (MMEJ) or theta-mediated end joining (TMEJ). Unlike other DNA repair polymerases, Pol θ is thought to be highly error prone, yet critical for cell survival. We have identified several mutations in the POLQ gene from human melanoma tumors. Through biochemical analysis, we have demonstrated that all three cancer-associated variants experienced altered DNA polymerase activity including a propensity for incorrect nucleotide selection and reduced polymerization rates compared to WT Pol θ. Moreover, the variants are 30 fold less efficient at incorporating a nucleotide during repair and up to 70 fold less accurate at selecting the correct nucleotide opposite a templating base. Taken together, this suggests that aberrant Pol θ has reduced DNA repair capabilities and may also contribute to increased mutagenesis. While this may be beneficial to normal cell survival, the variants were identified in established tumors suggesting that cancer cells may use this promiscuous polymerase to its advantage to promote metastasis and drug resistance.

Plastic responses to hot temperatures homogenize riparian leaf litter, speed decomposition, and reduce detritivores.

Efforts to maintain the function of critical ecosystems under climate change often begin with foundation species. In the southwestern United States, cottonwood trees support diverse communities in riparian ecosystems that are threatened by rising temperatures. Genetic variation within cottonwoods shapes communities and ecosystems, but these effects may be modified by phenotypic plasticity, where genotype traits change in response to environmental conditions. Here, we investigated plasticity in Fremont cottonwood (Populus fremontii) leaf litter traits as well as the consequences of plasticity for riparian ecosystems. We used three common gardens each planted with genotypes from six genetically divergent populations spanning a 12°C temperature gradient, and a decomposition experiment in a common stream environment. We found that leaf litter area, specific leaf area, and carbon to nitrogen ratio (C:N) were determined by interactions between genetics and growing environment, as was the subsequent rate of litter decomposition. Most of the genetic variation in leaf litter traits appeared among rather than within source populations with distinct climate histories. Source populations from hotter climates generally produced litter that decomposed more quickly, but plasticity varied the magnitude of this effect. We also found that hotter growing conditions reduced the variation in litter traits produced across genotypes, homogenizing the litter inputs to riparian ecosystems. All genotypes in the hottest garden produced comparatively small leaves that decomposed quickly and supported lower abundances of aquatic invertebrates, whereas the same genotypes in the coldest garden produced litter with distinct morphologies and decomposition rates. Our results suggest that plastic responses to climate stress may constrict the expression of genetic variation in predictable ways that impact communities and ecosystems. Understanding these interactions between genetic and environmental variation is critical to our ability to plan for the role of foundation species when managing and restoring riparian ecosystems in a warming world.

The Reliability of an Upper- and Lower-Extremity Visuomotor Reaction Time Task.

CONTEXT: Fast visuomotor reaction time (VMRT), the time required to recognize and respond to sequentially appearing visual stimuli, allows an athlete to successfully respond to stimuli during sports participation, while slower VMRT has been associated with increased injury risk. Light-based systems are capable of measuring both upper- and lower-extremity VMRT; however, the reliability of these assessments are not known. OBJECTIVE: To determine the reliability of an upper- and lower-extremity VMRT task using a light-based trainer system. DESIGN: Reliability study. SETTING: Laboratory. Patients (or Other Participants): Twenty participants with no history of injury in the last 12 months. METHODS: Participants reported to the laboratory on 2 separate testing sessions separated by 1 week. For both tasks, participants were instructed to extinguish a random sequence of illuminated light-emitting diode disks, which appeared one at a time as quickly as possible. Participants were provided a series of practice trials before completing the test trials. VMRT was calculated as the time in seconds between target hits, where higher VMRT represented slower reaction time. MAIN OUTCOME MEASURES: Separate intraclass correlation coefficients (ICCs) with corresponding 95% confidence intervals (CIs) were calculated to determine test-retest reliability for each task. The SEM and minimal detectable change values were determined to examine clinical applicability. RESULTS: The right limb lower-extremity reliability was excellent (ICC2,1 = .92; 95% CI, .81-.97). Both the left limb (ICC2,1 = .80; 95% CI, .56-.92) and upper-extremity task (ICC2,1 = .86; 95% CI, .65-.95) had good reliability. CONCLUSIONS: Both VMRT tasks had clinically acceptable reliability in a healthy, active population. Future research should explore further applications of these tests as an outcome measure following rehabilitation for health conditions with known VMRT deficits.

Discourse-based treatment in mild traumatic brain injury.

BACKGROUND: Individuals with traumatic brain injury (TBI) present with numerous discourse deficits associated with impairments to the linguistic system and other cognitive systems. Individuals with TBI may produce discourse that is lacking important information and poorly organized, as well as containing numerous coherence disrupting elements. Yet there are few studies directly addressing discourse deficits in individuals with TBI to guide clinicians. AIMS: The purpose of the study was to determine if discourse processing treatment improved the discourse production in individual with TBI. Aims of the study included determining if the discourse processing treatment improved completeness and informativeness in TBI discourse samples. METHODS & PROCEDURES: The study included three participants with mild-to-moderate TBI. The study utilized an A-B with maintenance design that incorporated components of functional practice, structured cues in the form of comprehension questions and story guide, and meta-cognitive and meta-linguistic processes. Discourse samples were obtained for baseline, treatment, and maintenance one-week and one-month post treatment. Stimuli included 12 sequential pictures, as well as a single picture and a recount probe. OUTCOMES & RESULTS: All participants demonstrated small gains in completeness and informativeness for treated items, and 2 of 3 participants demonstrated a medium therapeutic effect for untreated stimuli. Participants also produced discourse with fewer errors for both treated and untreated stimuli after treatment with no therapeutic effect to a small effect for the generalization stimuli. CONCLUSIONS: The study demonstrated that the discourse processing treatment is capable of producing small therapeutic effects that persisted one-month post treatment in adults with mild-to-moderate TBI.