A unique gender difference in early onset melanoma implies that in addition to ultraviolet light exposure other causative factors are important

Using US SEER17 Registry data, age‐specific melanoma incidence rates were calculated and comparisons were made between males and females. Relative Risk (RR) for males and females in each age group was computed and compared with that from Nordic Cancer Registry data set and to that for non‐melanoma skin cancer (NMSC). For age groups 44 and younger, females showed higher incidence rates, with a peak difference at age 20–24 (RR = 2.01, 95% CI = 1.21–3.33). Males exhibited higher incidence rates after age 44. The same bimodal gender difference was confirmed by the Nordic Cancer Registry data set, but it was not observed for NMSC, which is known to be strongly associated with cumulative exposure to solar UV radiation. We conclude that exposure to solar ultraviolet (UV) radiation is the major causative factor for melanoma at older age (>44 yr), but that other factors may play a role in early onset melanomas, particularly in females.     

Termite mounds differ in their importance for herbivores across savanna types,seasons and spatial scales

Herbivores do not forage uniformly across landscapes, but select for patches of higher nutrition and lower predation risk. Macrotermes mounds contain higher concentrations of soil nutrients and support grasses of higher nutritional value than the surrounding savanna matrix, attracting mammalian grazers that preferentially forage on termite mound vegetation. However, little is known about the spatial extent of such termite influence on grazing patterns and how it might differ in time and space. We measured grazing intensity in three African savanna types differing in rainfall and foliar nutrients and predicted that the functional importance of mounds for grazing herbivores would increase as the difference in foliar nutrient levels between mound and savanna matrix grasses increases and the mounds become more attractive. We expected this to occur in nutrient‐poor areas and during the dry season when savanna matrix grass nutrient levels are lower. Tuft use and grass N and P content were measured along transects away from termite mounds, enabling calculation of the spatial extent of termite influence on mammalian grazing. Using termite mound densities estimated from airborne light detection and ranging (LiDAR), we further upscaled field‐based results to determine the percentage of the landscape influenced by termite activity. Grasses in close proximity to termite mounds were preferentially grazed at all sites and in both seasons, but the strength of mound influence varied between savanna types and seasons. In the wet season, mounds had a relatively larger effect on grazers at the landscape scale in the nutrient‐poor, wetter savanna, whereas in the dry season the pattern was reversed with more of the landscape influenced at the nutrient‐rich, driest site. Our results reveal that termite mounds enhance the value of savanna landscapes for herbivores, but that their functional importance varies across savanna types and seasons.     

Modeling Patient-Derived Glioblastoma with Cerebral Organoids

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Oxidation and S-nitrosylation of cysteines in human cytosolic and mitochondrial glutaredoxins: effects on structure and activity

Glutathione (GSH) is the major intracellular thiol present in 1-10-mm concentrations in human cells. However, the redox potential of the 2GSH/GSSG (glutathione disulfide) couple in cells varies in association with proliferation, differentiation, or apoptosis from -260 mV to -200 or -170 mV. Hydrogen peroxide is transiently produced as second messenger in receptor-mediated growth factor signaling. To understand oxidation mechanisms by GSSG or nitric oxide-related nitrosylation we studied effects on glutaredoxins (Grx), which catalyze GSH-dependent thiol-disulfide redox reactions, particularly reversible glutathionylation of protein sulfhydryl groups. Human Grx1 and Grx2 contain Cys-Pro-Tyr-Cys and Cys-Ser-Tyr-Cys active sites and have three and two additional structural Cys residues, respectively. We analyzed the redox state and disulfide pairing of Cys residues upon GSSG oxidation and S-nitrosylation. Cytosolic/nuclear Grx1 was partly inactivated by both S-nitrosylation and oxidation. Inhibition by nitrosylation was reversible under anaerobic conditions; aerobically it was stronger and irreversible, indicating inactivation by nitration. Oxidation of Grx1 induced a complex pattern of disulfide-bonded dimers and oligomers formed between Cys-8 and either Cys-79 or Cys-83. In addition, an intramolecular disulfide between Cys-79 and Cys-83 was identified, predicted to have a profound effect on the three-dimensional structure. In contrast, mitochondrial Grx2 retains activity upon oxidation, did not form disulfide-bonded dimers or oligomers, and could not be S-nitrosylated. The dimeric iron sulfur cluster-coordinating inactive form of Grx2 dissociated upon nitrosylation, leading to activation of the protein. The striking differences between Grx1 and Grx2 reflect their diverse regulatory functions in vivo and also adaptation to different subcellular localization.     

Genetic association and functional studies of major polymorphic variants of MGMT

The DNA repair protein, O(6)-methylguanine DNA-methyltransferase (MGMT) prevents mutations and cell death that result from aberrant alkylation of DNA. The polymorphic variants Leu84Phe, Ile143Val, and Lys178Arg are frequent in the human population. We review here studies of these and other MGMT polymorphisms and their association with risk for lung, breast, colorectal and endometrial cancer with a consideration of gene-environment interactions. In addition, we review studies of the effects of polymorphic variation on alkyltransferase activity and expression. It is formally possible that polymorphic variation could modify functions of MGMT other than its alkyltransferase activity. While it was previously reported that an alkylated form of MGMT modifies Estrogen Receptor alpha activity, from our studies we conclude that this regulation is not a major function of MGMT. Overall, the effects of polymorphic variation on protein function are subtle, and further investigation is required to provide a comprehensive mechanism that explains the observed associations of these variants with risk for cancer.     

Alkyladenine DNA glycosylase (Aag) in somatic hypermutation and class switch recombination

Somatic hypermutation (SHM) and class switch recombination (CSR) of immunoglobulin (Ig) genes require the cytosine deaminase AID, which deaminates cytosine to uracil in Ig gene DNA. Paradoxically, proteins involved normally in error-free base excision repair and mismatch repair, seem to be co-opted to facilitate SHM and CSR, by recruiting error-prone translesion polymerases to DNA sequences containing deoxy-uracils created by AID. Major evidence supports at least one mechanism whereby the uracil glycosylase Ung removes AID-generated uracils creating abasic sites which may be used either as uninformative templates for DNA synthesis, or processed to nicks and gaps that prime error-prone DNA synthesis. We investigated the possibility that deamination at adenines also initiates SHM. Adenosine deamination would generate hypoxanthine (Hx), a substrate for the alkyladenine DNA glycosylase (Aag). Aag would generate abasic sites which then are subject to error-prone repair as above for AID-deaminated cytosine processed by Ung. If the action of an adenosine deaminase followed by Aag were responsible for significant numbers of mutations at A, we would find a preponderance of A:T>G:C transition mutations during SHM in an Aag deleted background. However, this was not observed and we found that the frequencies of SHM and CSR were not significantly altered in Aag-/- mice. Paradoxically, we found that Aag is expressed in B lymphocytes undergoing SHM and CSR and that its activity is upregulated in activated B cells. Moreover, we did find a statistically significant, albeit low increase of T:A>C:G transition mutations in Aag-/- animals, suggesting that Aag may be involved in creating the SHM A>T bias seen in wild type mice.     

Negative regulation of Ros receptor tyrosine kinase signaling. An epithelial function of the SH2 domain protein tyrosine phosphatase SHP-1

Male "viable motheaten" (me(v)) mice, with a naturally occurring mutation in the gene of the SH2 domain protein tyrosine phosphatase SHP-1, are sterile. Known defects in sperm maturation in these mice correlate with an impaired differentiation of the epididymis, which has similarities to the phenotype of mice with a targeted inactivation of the Ros receptor tyrosine kinase. Ros and SHP-1 are coexpressed in epididymal epithelium, and elevated phosphorylation of Ros in the epididymis of me(v) mice suggests that Ros signaling is under control of SHP-1 in vivo. Phosphorylated Ros strongly and directly associates with SHP-1 in yeast two-hybrid, glutathione S-transferase pull-down, and coimmunoprecipitation experiments. Strong binding of SHP-1 to Ros is selective compared to six other receptor tyrosine kinases. The interaction is mediated by the SHP-1 NH(2)-terminal SH2 domain and Ros phosphotyrosine 2267. Overexpression of SHP-1 results in Ros dephosphorylation and effectively downregulates Ros-dependent proliferation and transformation. We propose that SHP-1 is an important downstream regulator of Ros signaling.     

Molecular and catalytic properties of Arabidopsis thaliana adenylyl sulfate (APS)-kinase

A cDNA clone (Atakn1) from Arabidopsis thaliana encoding APS-kinase (EC 2.7.1.25) was investigated for structural and catalytic properties of the gene product. Recombinant his10-AtAkn1 formed PAPS at a Vmax of 7.35 U x mg(-1). The Km for APS was 0.14 microM and for ATP 147 microM. APS caused a severe substrate inhibition (K(i) 4.5 microM). The type of inhibition is uncompetitive with respect to MgATP. High ionic strength and reducing thiols stabilized the enzyme activity. Plant APS-kinase is regulated in vitro by the redox charge with thioredoxin as essential activator. Mutagenesis of a serine in S182C and S182F presumed to be involved in the transfer of the phosphoryl group had no effect upon catalytic activity. Using a yeast two-hybrid system with AtAkn1 as bait, an interacting clone was detected from a cDNA library of A. thaliana cv. Columbia that codes for an APS-kinase iso-form (Atakn2). Complementation of APS-kinase-deficient Saccharomyces cerevisiae met14 showed that AtAkn2 is functionally active as APS-kinase. It was immunologically related to AtAkn1 and presumably represents a plastidal iso-form of the plant APS-kinase gene family.