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Growth measurements on surface colonies of bacteria 总被引:4,自引:0,他引:4
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Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily that modulate target gene expression in response to fatty acid ligands. Their regulation by post-translational modifications has been reported but is poorly understood. In the present study, we investigated whether ligand binding affects the turnover and ubiquitination of the PPARbeta subtype (also known as PPARdelta). Our data show that the ubiquitination and degradation of PPARbeta is not significantly influenced by the synthetic agonist GW501516 under conditions of moderate PPARbeta expression. By contrast, the overexpression of PPARbeta dramatically enhanced its degradation concomitant with its polyubiquitination and the formation of high molecular mass complexes containing multiple, presumably oligomerized PPARbeta molecules that lacked stoichiometical amounts of the obligatory PPARbeta dimerization partner, retinoid X receptor. The formation of these apparently aberrant complexes, as well as the ubiquitination and destabilization of PPARbeta, were strongly inhibited by GW501516. Our findings suggest that PPARbeta is subject to complex post-translational regulatory mechanisms that partly may serve to safeguard the cell against deregulated PPARbeta expression. Furthermore, our data have important implications regarding the widespread use of overexpression systems to evaluate the function and regulation of PPARs. 相似文献
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During cardiac thin-filament activation, the N-domain of cardiac troponin C (N-cTnC) binds to Ca2+ and interacts with the actomyosin inhibitory troponin I (cTnI). The interaction between N-cTnC and cTnI stabilizes the Ca2+-induced opening of N-cTnC and is presumed to also destabilize cTnI–actin interactions that work together with steric effects of tropomyosin to inhibit force generation. Recently, our in situ steady-state FRET measurements based on N-cTnC opening suggested that at long sarcomere length, strongly bound cross-bridges indirectly stabilize this Ca2+-sensitizing N-cTnC–cTnI interaction through structural effects on tropomyosin and cTnI. However, the method previously used was unable to determine whether N-cTnC opening depends on sarcomere length. In this study, we used time-resolved FRET to monitor the effects of cross-bridge state and sarcomere length on the Ca2+-dependent conformational behavior of N-cTnC in skinned cardiac muscle fibers. FRET donor (AEDANS) and acceptor (DDPM)-labeled double-cysteine mutant cTnC(T13C/N51C)AEDANS-DDPM was incorporated into skinned muscle fibers to monitor N-cTnC opening. To study the structural effects of sarcomere length on N-cTnC, we monitored N-cTnC opening at relaxing and saturating levels of Ca2+ and 1.80 and 2.2-μm sarcomere length. Mg2+-ADP and orthovanadate were used to examine the structural effects of noncycling strong-binding and weak-binding cross-bridges, respectively. We found that the stabilizing effect of strongly bound cross-bridges on N-cTnC opening (which we interpret as transmitted through related changes in cTnI and tropomyosin) become diminished by decreases in sarcomere length. Additionally, orthovanadate blunted the effect of sarcomere length on N-cTnC conformational behavior such that weak-binding cross-bridges had no effect on N-cTnC opening at any tested [Ca2+] or sarcomere length. Based on our findings, we conclude that the observed sarcomere length-dependent positive feedback regulation is a key determinant in the length-dependent Ca2+ sensitivity of myofilament activation and consequently the mechanism underlying the Frank-Starling law of the heart. 相似文献
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Rieck M Arechiga A Onengut-Gumuscu S Greenbaum C Concannon P Buckner JH 《Journal of immunology (Baltimore, Md. : 1950)》2007,179(7):4704-4710
A variant of the PTPN22 gene, 1858C/T, is associated with an increased risk for the development of a wide array of autoimmune disorders. It is known that the protein tyrosine phosphatase Lyp encoded by this gene has an inhibitory effect on the proximal TCR signaling pathways. However, the consequences of carrying this variant and the mechanism by which it contributes to the development of autoimmunity are poorly understood. In this study, we demonstrate that homozygosity for this variant results in a profound deficit in T cell responsiveness to Ag stimulation. Heterozygosity for the variant allele is associated with reduced responsiveness of CD4+ memory T cells, characterized by diminished calcium mobilization, expression of CD25, and IL-10 production upon TCR stimulation. Additionally, the presence of the variant allele is associated with an increase in circulating memory T cells. We further demonstrate that these effects are not limited to the T cell compartment. Individuals with the variant allele have fewer memory B cells and these cells display a reduced response to stimulation via the BCR indicative of a B cell intrinsic defect. By identifying an immunologic phenotype in healthy subjects which correlates with the PTPN22 1858C/T genotype, we can now explore specific hypotheses regarding pathogenesis of diseases associated with the PTPN22 1858T variant. 相似文献