cDNA microarray analysis of altered gene expression in Ara-C-treated leukemia cells

The acute lymphoblastic leukemia cell line CCRF-CEM is sensitive to Ara-C and undergoes apoptosis. In contrast, the chronic myelogenous leukemia (CML) cell line K562 is highly resistant to Ara-C, which causes the cells to differentiate into erythrocytes before undergoing apoptosis. We used cDNA microarrays to monitor the alterations in gene expression in these two cell lines under conditions leading to apoptosis or differentiation. Ara-C-treated CCRF-CEM cells were characterized by a cluster of down-regulated chaperone genes, whereas Ara-C-treated K562 cells were characterized by a cluster of up-regulated hemoglobin genes. In K562 cells, Ara-C treatment induced significant down-regulation of the asparagine synthetase gene, which is involved in resistance to L-asparaginase. Sequential treatment with Ara-C and L-asparaginase had a synergistic effect on the inhibition of K562 cell growth, and combination therapy with these two anticancer agents may prove effective in the treatment of CML, which cannot be cured by either drug alone.     

Heterogeneous selection at specific loci in natural environments in Arabidopsis thaliana

Genetic variation for quantitative traits is often greater than that expected to be maintained by mutation in the face of purifying natural selection. One possible explanation for this observed variation is the action of heterogeneous natural selection in the wild. Here we report that selection on quantitative trait loci (QTL) for fitness traits in the model plant species Arabidopsis thaliana differs among natural ecological settings and genetic backgrounds. At one QTL, the allele that enhanced the viability of fall-germinating seedlings in North Carolina reduced the fecundity of spring-germinating seedlings in Rhode Island. Several other QTL experienced strong directional selection, but only in one site and seasonal cohort. Thus, different loci were exposed to selection in different natural environments. Selection on allelic variation also depended upon the genetic background. The allelic fitness effects of two QTL reversed direction depending on the genotype at the other locus. Moreover, alternative alleles at each of these loci caused reversals in the allelic fitness effects of a QTL closely linked to TFL1, a candidate developmental gene displaying nucleotide sequence polymorphism consistent with balancing selection. Thus, both environmental heterogeneity and epistatic selection may maintain genetic variation for fitness in wild plant species.     

Validity of NIR spectroscopy for quantitatively measuring muscle oxidative metabolic rate in exercise

The purpose of this studywas to examine the validity of the quantitative measurement of muscleoxidative metabolism in exercise by near-infrared continuous-wavespectroscopy (NIRcws). Twelve male subjects performed two bouts ofdynamic handgrip exercise, once for the NIRcws measurement and once forthe ³¹P-magnetic resonance spectroscopy (MRS) measurementas a standard measure. The resting muscle metabolic rate (RMRmus) wasindependently measured by ³¹P-MRS during 15 min of arterialocclusion at rest. During the first exercise bout, the quantitativevalue of muscle oxidative metabolic rate at 30 s postexercisewas evaluated from the ratio of the rate of oxyhemoglobin/myoglobindecline measured by NIRcws during arterial occlusion 30 s afterexercise and the rate at rest. Therefore, the absolute values of muscleoxidative metabolic rate at 30 s after exercise[O_2NIR(30)] wascalculated from this ratio multiplied by RMRmus. During the secondexercise bout, creatine phosphate (PCr) resynthesis rate was measuredby ³¹P-MRS at 30 s postexercise[Q₍₃₀₎] under the same conditions but without arterial occlusion postexercise. To determine the validity ofNIRcws, O_2NIR(30) wascompared with Q₍₃₀₎. There was a significant correlation betweenO_2NIR(30), which rangedbetween 0.018 and 0.187 mM ATP/s, and Q₍₃₀₎,which ranged between 0.041 and 0.209 mM ATP/s (r = 0.965, P < 0.001). This result supports theapplication of NIRcws to quantitatively evaluate muscle oxidativemetabolic rate in exercise.

     

Production of D-amino acid oxidase (DAO) of Trigonopsis variabilis in Schizosaccharomyces pombe and the characterization of biocatalysts prepared with recombinant cells

The cDNA of D-amino acid oxidase (DAO) gene isolated from Trigonopsis variabilis was expressed in Schizosaccharomyces pombe. A clone, ASP327-10, transformed with plasmid vector, pTL2M5DAO, expressed catalytically active DAO in the presence of G418, and converted Cephalosprin C to alpha-ketoadipyl-7-cephalosporanic acid (KA-7-ACA) and glutaryl-7-aminocephalosporanic acid (GL-7-ACA). Biocatalysts were prepared using ASP327-10 and T. variabilis, and evaluated to demonstrate the feasibility of recombinant S. pombe for industrial application. The cells were immobilized by crosslinking polyethylene imine after glutardialdehyde (GDA) fixation and permeabilization by alkaline treatment. Although the biocatalyst prepared from ASP327-10 exhibited DAO activity, catalase activity still remained fully even after permeabilization, under which condition, the catalase activity of T. variabilis decreased to 20-30%. Heat treatment was required before cell fixation by GDA to inactivate the catalase in S. pombe. This improved the efficiency of bioconversion to GL-7-ACA, but caused poor mechanical strength in the biocatalyst of S. pombe. To overcome this weakness, a catalase-deficient host strain was obtained by ethylmethansulfate mutagenesis. Moreover, taking economics into consideration, the integrative vector, pTL2M5DAO-8XL, with multi-copies of expression cassette was constructed to express DAO in S. pombe even in the absence of G418. The newly established integrant, ASP417-7, did not exhibit any catalase activity so that heat treatment was not required. The obtained integrant and its biocatalyst were significantly improved in GL-7ACA conversion ability and mechanical strength. This study demonstrates that the established integrant is a potential candidate as an alternative source of DAO enzyme.     

Differential sensitivity between Fks1p and Fks2p against a novel beta -1,3-glucan synthase inhibitor,aerothricin3 [corrected

Fks1p and Fks2p are catalytic subunits of beta-1,3-glucan synthase, which synthesize beta-1,3-glucan, a main component of the cell wall in Saccharomyces cerevisiae. Although Fks1p and Fks2p are highly homologous, sharing 88.1% identity, it has been shown that Fks2p is more sensitive than Fks1p to one of echinocandin derivatives, which inhibits beta-1,3-glucan synthase activity. Here we show a similar differential sensitivity between Fks1p and Fks2p to a novel beta-1,3-glucan synthase inhibitor, aerothricin3 [corrected]. To investigate the molecular mechanism of this differential sensitivity, we constructed a series of chimeric genes of FKSs and examined their sensitivity to aerothricin3 [corrected]. As a result, it was shown that a region around the fourth extracellular domain of Fks2p, containing 10 different amino acid residues from those of Fks1p, provided Fks1p aerothricin3 [corrected] sensitivity when the region was replaced with a corresponding region of Fks1p. In order to identify essential amino acid residues responsible for the sensitivity, each of the 10 non-conserved amino acids of Fks1p was substituted into the corresponding amino acid of Fks2p by site-directed mutagenesis. Surprisingly, only one amino acid substitution of Fks1p (K1336I) conferred Fks1p hypersensitivity to aerothricin3 [corrected]. On the other hand, reverse substitution of the corresponding amino acid of Fks2p (I1355K) resulted in loss of hypersensitivity to aerothricin3 [corrected]. These results suggest that the 1355th isoleucine of Fks2p plays a key role in aerothricin3 [corrected] sensitivity.     

The leukocyte common antigen (CD45) of the Pacific hagfish,Eptatretus stoutii: implications for the primordial function of CD45

CD45, originally known as the leukocyte common antigen, is a prototypical transmembrane protein tyrosine phosphatase that plays a critical role in signal transduction through T-cell and B-cell receptors, as well as in T-cell and B-cell development. In the present study, we show that the Pacific hagfish, widely believed to lack the adaptive immune system, has CD45. The presence of CD45 in jawless fish is consistent with the recent discovery that CD45 also plays a crucial role in innate immunity via the regulation of signaling through type I and type II cytokine receptors. It is likely that CD45 was recruited to activate lymphocytes through antigen receptors encoded by rearranging genes in jawed vertebrates.