ATR-dependent checkpoint modulates XPA nuclear import in response to UV irradiation.

In response to DNA damage, mammalian cells activate various DNA repair pathways to remove DNA lesions and, meanwhile, halt cell cycle progressions to allow sufficient time for repair. The nucleotide excision repair (NER) and the ATR-dependent cell cycle checkpoint activation are two major cellular responses to DNA damage induced by UV irradiation. However, how these two processes are coordinated in the response is poorly understood. Here we showed that the essential NER factor XPA (xeroderma pigmentosum group A) underwent nuclear accumulation upon UV irradiation, and strikingly, such an event occurred in an ATR (Ataxia-Telangiectasia mutated and RAD3-related)-dependent manner. Either treatment of cells with ATR kinase inhibitors or transfection of cells with small interfering RNA targeting ATR compromised the UV-induced XPA nuclear translocation. Consistently, the ATR-deficient cells displayed no substantial XPA nuclear translocation while the translocation remained intact in ATM (Ataxia-Telangiectasia mutated)-deficient cells in response to UV irradiation. Moreover, we found that ATR is required for the UV-induced nuclear focus formation of XPA. Taken together, our results suggested that the ATR checkpoint pathway may modulate NER activity through the regulation of XPA redistribution in human cells upon UV irradiation.

Effects of high-intensity resistance training on untrained older men. II. Muscle fiber characteristics and nucleo-cytoplasmic relationships.

During growth and repair of skeletal muscle fibers, satellite cells become activated, undergo mitosis, and a daughter nucleus becomes incorporated into the muscle fiber to increase myonuclear numbers. An increase in myonuclei appears to be required for this postnatal growth. This study examined whether muscle fibers of elderly men can hypertrophy with strength training and, if so, whether they have the capacity to incorporate nuclei into the fibers. The sarcoplasmic area associated with each myonucleus was calculated in nine elderly men before and after 16 weeks of strength training, and compared to nine elderly control men. Muscle fiber type changes and myosin heavy chain composition were also compared. All major fiber types (I, IIA, IIB) became significantly larger after training, and a transition of type IIB fibers to IIA occurred with training. The area occupied by each fiber type correlated with myosin heavy chain percentage, and both of these changed similarly with strength training. The cytoplasm-to-myonucleus ratio increased, but not significantly (p = .07), with muscle fiber hypertrophy. Number of myonuclei per fiber and myonuclei per unit length of muscle fiber increased, but not significantly. Cross-sectional areas of the muscle fibers in untrained elderly men were much smaller than in untrained young men (when compared with our earlier studies). Training increased the sizes of the elderly muscle fibers to that of the untrained young men. This hypertrophy of muscle fibers by 30% with training resulted in no change in the cytoplasm-to-myonucleus ratio. This suggests that the myonuclear population continues to adapt to growth stimuli in the elderly muscles.

The affinity glycated hemoglobin in a family with hereditary spherocytosis and in other non-hemoglobinopathic hemolytic anemias.

The glycated hemoglobin (GHb) is lowered by hemolytic anemia. The cation-exchange HbA1 has been shown to be lowered by hereditary spherocytosis (HS). The HbA1, however, can be increased by elevations of fetal hemoglobin (HbF). The affinity GHb, a parameter related to, but not identical with, the HbA1, and unaffected by HbF, has been shown to be low in hemoglobinopathies but not, to our knowledge, in HS and other non-hemoglobinopathic hemolytic anemias. Therefore, the affinity GHb and HbF was determined in four members of an HS family and in nine other cases of non-hemoglobinopathic hemolytic anemia, including three autoimmune hemolytic anemias, four red cell fragmentation syndromes (two "Waring blender" syndromes, one thrombotic thrombocytopenic purpura in association with tumor, and one case of disseminated intravascular coagulation), and two red cell membrane defects: paroxysmal nocturnal hemoglobinuria and another case of hereditary spherocytosis. The GHb for these nine cases was 3.6 +/- 1.7 percent (normal 6.0 +/- 2.0 percent; p less than 0.001). The reticulocyte count, available in four cases, was 0.23 +/- 0.14 and correlated negatively with the GHb. The average GHb in the HS family was 3.9 +/- 0.8 percent, which was significantly less than the normal of 6.0 +/- 2.0 percent (p less than 0.001); the HbF was less than 1.0 percent. It is concluded that the GHb is diminished in hemolytic anemias not associated with hemoglobinopathies and that this lowering reflects the shortened red cell life span in these processes. To our knowledge, this is the first report of low GHb in hemolytic anemia not associated with hemoglobinopathy, by the affinity chromatographic technique, as opposed to the cation-exchange chromatographic technique.

Densitometry and microchromatography compared for determination of the hemoglobin C and A2 proportions in hemoglobin C and hemoglobin SC disease and in hemoglobin C trait.

Using both densitometry and anion-exchange microchromatography, we measured hemoglobin C (Hb C) and Hb A2 proportions in 11 patients, eight of whom had Hb AC, two Hb SC, and one Hb CC. For one patient with Hb SC, we made the determinations before and after a transfusion. The mean (and SD) for the sum of Hb C + Hb A2 by densitometry and anion-exchange microchromatography for the nine patients with Hb AC and Hb CC were 45 (18) and 40 (18)%, respectively (p greater than 0.1, r = 0.98); for the three determinations involving the two Hb SC patients, the respective proportions were 40 (9.9) and 38 (6.6)% (r = 0.88). Electrophoretic analysis of microchromatographic eluates from the Hb AC and Hb CC patients showed that 6% of the absorbance of the late high-ionic-strength eluate was due to Hb C, which was responsible for the statistically insignificant difference between densitometric and chromatographic values for Hb C + A2 values. Electrophoresis on cellulose acetate of concentrated eluates of the Hb C + A2 fraction from the two Hb SC patients revealed no contamination by Hb S. Evidently, microchromatography can be used to determine Hb C + A2 in patients with Hb C or Hb SC disease or Hb C trait.