SIX4 Controls Anti-PD-1 Efficacy by Regulating STING Expression.

The cGAS/STING cytosolic DNA-sensing pathway plays a significant role in antitumor immunity. Expression of STING is tightly regulated and commonly reduced or defective in many types of cancer. We have identified SIX4 as a significant regulator of STING expression in colon cancer cells. We showed that knockout of SIX4 decreased STING expression at the mRNA and protein levels while ectopic expression of SIX4 increased STING expression. Depletion of SIX4 led to attenuated STING activation and downstream signaling. Reexpression of SIX4 or ectopic expression of STING in SIX4 knockout cells reversed the effect. Ectopic expression of SIX4 enhanced DMXAA and cGAMP-induced STING activation and downstream signaling. Importantly, decrease of SIX4 expression substantially decreased tumor infiltration of CD8+ T cells and reduced the efficacy of PD-1 antibodies to diminish tumor growth in immune competent mice in vivo. Finally, analysis of The Cancer Genome Atlas colon cancer dataset indicated that tumors with high SIX4 expression were significantly enriched in the Inflammatory Response pathway. SIX4 expression also correlated with expression of multiple IFN-stimulated genes, inflammatory cytokines, and CD8A. Taken together, our results implicate that SIX4 is a principal regulator of STING expression in colon cancer cells, providing an additional mechanism and genetic marker to predict effective immune checkpoint blockade therapy responses. SIGNIFICANCE: Our studies demonstrate that SIX4 is an important regulator of STING expression, providing a genetic marker or a therapeutic target to predict or enhance immune checkpoint blockade therapy responses in colon cancer.

Ion Substitution Strategy of Manganese-Based Layered Oxide Cathodes for Advanced and Low-Cost Sodium Ion Batteries.

Sodium ion batteries (SIBs) have recently been promising in the large-scale electric energy storage system, due to the low cost, abundant sodium resources. Mn-based layered oxide cathode materials have been widely investigated, because of the high theoretical specific capacity, low cost, and abundant reserves. However, their development is limited by the problems of Jahn-Teller distortion, Na+ /vacancy ordering, complex phase transitions, and irreversible anionic redox during cycling. Ion substitution strategy is one simple and effective way to regulate the crystal structure and boost sodium-storage performances of Mn-based cathode materials. In this review, we summarize the progress and mechanism of ion-substituted Mn-based oxides, establish a composition-crystal structure-electrochemical performance relationship, and also offer perspectives for guiding the design of high-performance Mn-based oxides for SIBs.

Polymerase Epsilon-Associated Ultramutagenesis in Cancer.

With advances in next generation sequencing (NGS) technologies, efforts have been made to develop personalized medicine, targeting the specific genetic makeup of an individual. Somatic or germline DNA Polymerase epsilon (PolE) mutations cause ultramutated (>100 mutations/Mb) cancer. In contrast to mismatch repair-deficient hypermutated (>10 mutations/Mb) cancer, PolE-associated cancer is primarily microsatellite stable (MSS) In this article, we provide a comprehensive review of this PolE-associated ultramutated tumor. We describe its molecular characteristics, including the mutation sites and mutation signature of this type of tumor and the mechanism of its ultramutagenesis. We discuss its good clinical prognosis and elucidate the mechanism for enhanced immunogenicity with a high tumor mutation burden, increased neoantigen load, and enriched tumor-infiltrating lymphocytes. We also provide the rationale for immune checkpoint inhibitors in PolE-mutated tumors.

Cation-Disordered O3-Na0.8Ni0.6Sb0.4O2 Cathode for High-Voltage Sodium-Ion Batteries.

O3-type sodium-layered oxides (such as antimony-based O3 structures) have been suggested as one of the most fascinating cathode materials for sodium-ion batteries (SIBs). Honeycomb-ordered antimony-based O3 structures, however, unsatisfactorily exhibit complex phase transitions and sluggish Na+ kinetics during cycling. Herein, we prepared a completely cationic-disordered O3-type Na0.8Ni0.6Sb0.4O2 compound by composition regulation for SIBs. Surprisingly, the measured redox potentials for typical O3-P3 phase transition are located at 3.4 V. Operando X-ray diffraction confirms a reversible phase transition process from the O3 to P3 structure accompanied with a very small volume change (1.0%) upon sodium extraction and insertion. The low activation barrier energy of 400 meV and the fast Na+ migration of 10-11 cm2·s-1 are further obtained by first-principles calculations and galvanostatic intermittent titration technique, respectively. As a result, the O3-Na0.8Ni0.6Sb0.4O2 cathode displays a reversible capacity of 106 mA h g-1 at 0.1C (12 mA g-1), smooth charge-discharge curves, and a high average working voltage of 3.5 V during battery cycling. The results highlight the importance of searching for a new O3-type structure with cation-disordering and high working voltage for realizing high energy SIBs.

Mismatch repair and DNA polymerase δ proofreading prevent catastrophic accumulation of leading strand errors in cells expressing a cancer-associated DNA polymerase ϵ variant.

Substitutions in the exonuclease domain of DNA polymerase ϵ cause ultramutated human tumors. Yeast and mouse mimics of the most common variant, P286R, produce mutator effects far exceeding the effect of Polϵ exonuclease deficiency. Yeast Polϵ-P301R has increased DNA polymerase activity, which could underlie its high mutagenicity. We aimed to understand the impact of this increased activity on the strand-specific role of Polϵ in DNA replication and the action of extrinsic correction systems that remove Polϵ errors. Using mutagenesis reporters spanning a well-defined replicon, we show that both exonuclease-deficient Polϵ (Polϵ-exo-) and Polϵ-P301R generate mutations in a strictly strand-specific manner, yet Polϵ-P301R is at least ten times more mutagenic than Polϵ-exo- at each location analyzed. Thus, the cancer variant remains a dedicated leading-strand polymerase with markedly low accuracy. We further show that P301R substitution is lethal in strains lacking Polδ proofreading or mismatch repair (MMR). Heterozygosity for pol2-P301R is compatible with either defect but causes strong synergistic increases in the mutation rate, indicating that Polϵ-P301R errors are corrected by Polδ proofreading and MMR. These data reveal the unexpected ease with which polymerase exchange occurs in vivo, allowing Polδ exonuclease to prevent catastrophic accumulation of Polϵ-P301R-generated errors on the leading strand.

DNA polymerase δ proofreads errors made by DNA polymerase ε.

During eukaryotic replication, DNA polymerases ε (Polε) and δ (Polδ) synthesize the leading and lagging strands, respectively. In a long-known contradiction to this model, defects in the fidelity of Polε have a much weaker impact on mutagenesis than analogous Polδ defects. It has been previously proposed that Polδ contributes more to mutation avoidance because it proofreads mismatches created by Polε in addition to its own errors. However, direct evidence for this model was missing. We show that, in yeast, the mutation rate increases synergistically when a Polε nucleotide selectivity defect is combined with a Polδ proofreading defect, demonstrating extrinsic proofreading of Polε errors by Polδ. In contrast, combining Polδ nucleotide selectivity and Polε proofreading defects produces no synergy, indicating that Polε cannot correct errors made by Polδ. We further show that Polδ can remove errors made by exonuclease-deficient Polε in vitro. These findings illustrate the complexity of the one-strand-one-polymerase model where synthesis appears to be largely divided, but Polδ proofreading operates on both strands.

A recurrent cancer-associated substitution in DNA polymerase ε produces a hyperactive enzyme.

Alterations in the exonuclease domain of DNA polymerase ε (Polε) cause ultramutated tumors. Severe mutator effects of the most common variant, Polε-P286R, modeled in yeast suggested that its pathogenicity involves yet unknown mechanisms beyond simple proofreading deficiency. We show that, despite producing a catastrophic amount of replication errors in vivo, the yeast Polε-P286R analog retains partial exonuclease activity and is more accurate than exonuclease-dead Polε. The major consequence of the arginine substitution is a dramatically increased DNA polymerase activity. This is manifested as a superior ability to copy synthetic and natural templates, extend mismatched primer termini, and bypass secondary DNA structures. We discuss a model wherein the cancer-associated substitution limits access of the 3'-terminus to the exonuclease site and promotes binding at the polymerase site, thus stimulating polymerization. We propose that the ultramutator effect results from increased polymerase activity amplifying the contribution of Polε errors to the genomic mutation rate.

Sulfolobus replication factor C stimulates the activity of DNA polymerase B1.

Replication factor C (RFC) is known to function in loading proliferating cell nuclear antigen (PCNA) onto primed DNA, allowing PCNA to tether DNA polymerase for highly processive DNA synthesis in eukaryotic and archaeal replication. In this report, we show that an RFC complex from the hyperthermophilic archaea of the genus Sulfolobus physically interacts with DNA polymerase B1 (PolB1) and enhances both the polymerase and 3'-5' exonuclease activities of PolB1 in an ATP-independent manner. Stimulation of the PolB1 activity by RFC is independent of the ability of RFC to bind DNA but is consistent with the ability of RFC to facilitate DNA binding by PolB1 through protein-protein interaction. These results suggest that Sulfolobus RFC may play a role in recruiting DNA polymerase for efficient primer extension, in addition to clamp loading, during DNA replication.