Serum response factor (SRF), a member of the MCM1, agamous, deficiens, SRF (MADS) family of transcriptional activators, has been implicated in the transcriptional control of a number of cardiac muscle genes, including cardiac alpha-actin, skeletal alpha-actin, alpha-myosin heavy chain (alpha-MHC), and beta-MHC. To better understand the in vivo role of SRF in regulating genes responsible for maintenance of cardiac function, we sought to test the hypothesis that increased cardiac-specific SRF expression might be associated with altered cardiac morphology and function. We generated transgenic mice with cardiac-specific overexpression of the human SRF gene. The transgenic mice developed cardiomyopathy and exhibited increased heart weight-to-body weight ratio, increased heart weight, and four-chamber dilation. Histological examination revealed cardiomyocyte hypertrophy, collagen deposition, and interstitial fibrosis. SRF overexpression altered the expression of SRF-regulated genes and resulted in cardiac muscle dysfunction. Our results demonstrate that sustained overexpression of SRF, in the absence of other stimuli, is sufficient to induce cardiac change and suggest that SRF is likely to be one of the downstream effectors of the signaling pathways involved in mediating cardiac hypertrophy.

The pK values of thermospermine, a novel asymmetric tetraamine (4,8-diazadodecane-l,12-diamine), have been determined for the first time by the conventional titration method with subsequent data analyses. It was found to be the most basic polyamine among naturally occurring tetraamines. The I5N N M R titration method was applied to determine its protonation site. Natural-abundance I5N magnetic resonance spectra of the polyamine have been recorded as a function of pH from its free to the protonated form. Its apparent pK values, as well as the intrinsic chemical shifts for each stage of protonation, have been calculated from the N M R titration curve by using a nonlinear least-squares method. The four protonation sites of thermospermine have been successfully determined to be Nt2, N', N-8, and N-4 in chat order from the free to the completely protonated form. In a similar manner the protonation sites of spermidine and two symmetric tetraamines, thermine and spermine, have been established. I3C N M R experiments for the four polyamines were almost consistent with those of I5N NMR. Owing to the much higher concentration of the polyamines furnished for N M R titration experiments, the pK values obtained by NMR were larger than those derived by the conventional titration methods.A considerable number of observations show a correlation of enhanced synthesis of polyamines with rapid growth or cell proliferation [1,2]. From the point of view of the physiological role of polyamines in cells, polyamines were implicated as regulators of cell proliferative activity [3-S]. Thus it is tempting to speculate that association as well as dissociation of polyamines with biological macromolecules may be controlled dynamically. In fact, it has been shown that polyamines can bind with nucleic acids [S -81 and that they exert a remarkable stabilization of a teritary structure of the nucleic acids [9 -121. This led us to determine the protonation sites in polyamines and the corresponding pK values, and to examine their effect on the interaction with biological macromolecules.The pK values of several naturally occurring and synthetic polyamines have been determined by means of potentiometric titration methods [I 3 -IS]. However, the pK values of thermospermine, i.e. 4,s-diazadodecane-l , 12-diamine have remained undetermined. This polyamine is a new asymmetric tetraamine which was found in an extremely thermophilic microorganism, Thermus tl~rrmnphilus, and its structure has been determined [16]. Thus we synthesized it and measured the p K values by potentiometric titration.Determination of the protonation sites in polyamines has been attempted by calorimetric measurements [I 7,181 and the calculation of protonation enthalpy by applying quantum chemical methods [I 91. These attempts were almost successfull, but they are indirect methods. NMR titration, on the other hand, provides pK values and information about the protonation pattern, since chemical shifts of the nuclei at the basic sites are often markedly influenced by the ionization o...

Our newly designed image-guided radiotherapy (IGRT) system enables the dynamic tracking irradiation with a gimbaled X-ray head and a dual on-board kilovolt imaging subsystem for real-time target localization. Examinations using a computer-controlled three-dimensionally movable phantom demonstrated that our gimbals tracking system significantly reduced motion blurring effects in the dose distribution compared to the non-tracking state.

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