Novel Role of Glycogen Synthase Kinase-3β in Determining Cancer Cell Response to Genotoxic Stress through Regulation of 53BP1 Function

PURPOSE/OBJECTIVE(S)

Glycogen synthase kinase-3β (GSK3β) is a multifunctional serine/threonine kinase involved in various cellular processes and signaling pathways. Accumulating evidence suggests GSK3β plays a role in cancer treatment with effects on tumorigenesis and treatment response. We have previously shown that inhibition of GSK3β protects neurons from ionizing radiation-induced apoptosis through upregulation of non-homologous end joining (NHEJ) mediated repair of double strand breaks (DSBs). Here, we investigate the molecular mechanism underlying GSK3β regulation of NHEJ.

MATERIALS/METHODS

Using biochemical, molecular, and genetic approaches, we investigated the physical and functional interaction between GSK3β and 53BP1. Cultured human tumor cells were utilized as model system to further characterize how GSK3β controls 53BP1 function in DNA DSB recognition and repair. Finally, we employed a cell biology approach to genetically and pharmacologically manipulate GSK3β activity and test how the GSK3β-53BP1 axis impacts tumor cytotoxic response to PARP inhibitor (PARPi) and radiation therapy.

RESULTS

We illustrate that GSK3β directly interacts with 53BP1 and phosphorylates 53BP1 at threonine 334 amino acid (T334) within a region heavily phosphorylated by several stress kinases. Phosphorylation at T334 inhibits 53BP1's function in recruitment to DNA DSB sites as well as canonical NHEJ. Furthermore, our results identify GSK3β regulation of 53BP1 function in NHEJ is achieved through suppression of downstream mediators, RIF1 and PTIP, and their function. In contrast, GSK3β enhances single strand DNA resection and promotes homologous recombination (HR) repair. Most importantly, genetic and pharmacologic inhibition of GSK3β-53BP1 signaling axis dramatically enhances the cytotoxic response of BRCA1-deficit cancer cells to PARPi. The assessment of the effect of GSK3β-53BP1 axis on tumor cell response to radiation treatment is underway.

CONCLUSION

This study establishes the connection between GSK3β and DSB repair through its phosphorylation and regulation of 53BP1 pathways. Moreover, it demonstrates that GSK3β kinase activity uniquely results in inhibition of 53BP1 as opposed to other kinases that enhance 53BP1 function. Importantly, this novel signaling axis provides a strategy for targeting cancer cell resistance to PARPi.

Magnetic, magnetocaloric and magnetoresistive properties of cubic Laves phase HoAl2 single crystal

We report the magnetization (M) and magnetoresistance (MR) results of HoAl2 single crystals oriented along the ⟨100⟩ and ⟨110⟩ directions. Although HoAl2 has cubic Laves phase structure, a large anisotropy is observed in M and MR below the Curie temperature (TC). A satisfactory correlation between magnetic entropy change (ΔSM) and MR could be established along ⟨110⟩ and also ⟨100⟩, except for the temperature (T) region around which spin reorientation takes place. Large inverse magnetocaloric effect is observed at low T, which is associated with the spin reorientation process in the ⟨100⟩ direction. A theoretical model based on the Landau theory of phase transition can describe the T-variation of -ΔSM for T > TC.

Exchange bias effect in alloys and compounds

The phenomenology of exchange bias effects observed in structurally single-phase alloys and compounds but composed of a variety of coexisting magnetic phases such as ferromagnetic, antiferromagnetic, ferrimagnetic, spin-glass, cluster-glass and disordered magnetic states are reviewed. The investigations on exchange bias effects are discussed in diverse types of alloys and compounds where qualitative and quantitative aspects of magnetism are focused based on macroscopic experimental tools such as magnetization and magnetoresistance measurements. Here, we focus on improvement of fundamental issues of the exchange bias effects rather than on their technological importance.

Grain size effect on the magnetic cluster-glass properties of La0.88Sr0.12CoO3

We report the grain size effect of hole-doped cobaltite, La(0.88)Sr(0.12)CoO(3), where average sizes are varied from ∼35 to ∼240 nm. The bulk compound is a cluster-glass (CG) compound composed of short range ferromagnetic (FM) clusters embedded in the spin-glass (SG) matrix at low temperature. The short range FM clusters are still retained in the nanocrystalline compound with average size ∼35 nm which are associated with the SG component, displaying CG-like spin dynamics at low temperature. The exchange bias (EB) effect manifested by the shifts in the hysteresis loop is observed due to the field cooling where EB effect is weakened systematically with decreasing grain size. The decrease in the fraction of the FM component is found to be correlated with the weakening of the EB effect with decreasing grain size. Interestingly, the signature of the EB phenomenon due to the field-cooled effect is also evidenced in the temperature as well as the time dependence of resistivity. The grain interior phase separation scenario around the FM/SG interface region has been proposed to interpret the experimental results.

Exchange bias effect and intragranular magnetoresistance in Nd(0.84)Sr(0.16)CoO(3)

Electrical transport properties as a function of magnetic field and time have been investigated in polycrystalline, Nd(0.84)Sr(0.16)CoO(3). A strong exchange bias (EB) effect is observed associated with the fairly large intragranular magnetoresistance (MR). The EB effect observed in the MR curve is compared with the EB effect manifested in the magnetic hysteresis loop. A training effect, described as the decrease of EB effect when the sample is successively field cycled at a particular temperature, has been observed in the shift of the MR curve. The training effect could be analyzed by successful models. The EB effect, MR and a considerable time dependence in MR are attributed to the intrinsic nanostructure giving rise to varieties of magnetic interfaces in the grain interior.

The exchange bias effect in phase separated Nd(1-x)Sr(x)CoO(3) at the spontaneous ferromagnetic/ferrimagnetic interface

We report new results for the exchange bias effect in Nd(1-x)Sr(x)CoO(3) for x = 0.20 and 0.40, where the exchange bias phenomenon is involved with the ferrimagnetic (FI) state in a spontaneously phase separated system. The zero-field-cooled magnetization exhibits FI (T(FI)) and ferromagnetic (FM; T(C)) transitions at ∼23 and ∼70 K, respectively, for x = 0.20. Negative horizontal and positive vertical shifts of the magnetic hysteresis loops are observed when the system is cooled through T(FI) in a positive static magnetic field. A training effect is observed for x = 0.20, which could be interpreted satisfactorily by the spin configurational relaxation model. The unidirectional shifts of the hysteresis loops as a function of temperature exhibit an absence of exchange bias above T(FI) for x = 0.20. Analysis of the cooling field dependence of the exchange bias field and magnetization indicates that the FM clusters consist of a single magnetic domain with an average size of around ∼20 and ∼40 Å for x = 0.20 and 0.40, respectively. The sizes of the FM clusters are close to the percolation threshold for x = 0.20; these grow and coalesce to form the bigger size for x = 0.40 resulting in a weak exchange bias effect.

Reply to comment on 'Particle size dependent exchange bias and cluster-glass states in LaMn(0.7)Fe(0.3)O(3) '

In reply to the comment by Geshev we emphasize that loop shift in the compounds is not a simplified phenomenon of minor loop effect of a ferromagnet rather, it is a genuine signature of exchange bias effect. The estimate of anisotropy field and the plot of exchange bias field at 5 K with the maximum field used for the measurement of hysteresis loop, in addition to the previously reported results such as temperature dependence of exchange bias field, training effect, etc, confirm the exchange bias effect.

Characterization of cytotoxin-producing Aeromonas caviae (strain HT10) isolated from a sulfur spring in Orissa, India

During a study of microbial diversity, a bacterial strain designated HT10, was isolated from sediment collected from an unexplored sulfur spring at Athamallik, Orissa, India. Various biochemical tests and 16S rDNA sequence analysis revealed that strain HT10 is Aeromonas caviae. The growth temperature of this strain ranged from 12 to 43 degrees C and the optimum temperature was 30 degrees C. The strain HT10 showed cytotoxic and alpha-hemolytic activity. This is the first report on the isolation of Aeromonas caviae from sulfur spring.

Evaluation of mercury toxicity by some cytological indices in leucocyte cultures

The genotoxicity induced by different levels of inorganic mercury was evaluated by chromosome metaphase analysis in human leucocytes, treated in vitro for 72 hr. Mitotic index gradually decreased with an increase in concentration of mercury but the reverse phenomenon was observed with respect to chromosomal aberration due to its probable interaction with protein and DNA.

Role of Sulfur Compounds in the Detection of Amino Acids by Ninhydrin on TLC Plate

Three new sulfur reagents for specific identification of amino acids on thin-layer chromatography plates have been introduced. These three sulfur containing reagents are capable of developing various distinguishable colors with many of them. A probable mechanism for such color formation is proposed.

Molecular dynamics simulations of lipid bilayers: major artifacts due to truncating electrostatic interactions

We study the influence of truncating the electrostatic interactions in a fully hydrated pure dipalmitoylphosphatidylcholine (DPPC) bilayer through 20 ns molecular dynamics simulations. The computations in which the electrostatic interactions were truncated are compared to similar simulations using the particle-mesh Ewald (PME) technique. All examined truncation distances (1.8-2.5 nm) lead to major effects on the bilayer properties, such as enhanced order of acyl chains together with decreased areas per lipid. The results obtained using PME, on the other hand, are consistent with experiments. These artifacts are interpreted in terms of radial distribution functions g(r) of molecules and molecular groups in the bilayer plane. Pronounced maxima or minima in g(r) appear exactly at the cutoff distance indicating that the truncation gives rise to artificial ordering between the polar phosphatidyl and choline groups of the DPPC molecules. In systems described using PME, such artificial ordering is not present.

Decay rate distributions of disordered slabs and application to random lasers

We compute the distribution of the decay rates (also referred to as residues) of the eigenstates of a disordered slab from a numerical model. From the results of the numerical simulations, we are able to find simple analytical formulas which describe these results well. This is possible for samples both in the diffusive and in the localized regimes. As an example of a possible application, we investigate the lasing threshold of random lasers.