| dc.description.abstract | The involvement of E-boxes in MyoD-mediated M-cadherin activation
The muscle regulatory factor (MRF) family has been known to regulate myogenic cell lineage determination and terminal differentiation of myotubes through targeting consensus enhancer box (E-box). Targeting of MRFs to E-boxes presented in promoter or enhancer region of myogenic genes is important for controlling myogenesis process. According to previous study, MyoD was able to target E-boxes around M-cadherin proximal promoter (-252~+200bp) to activate M-cadherin transcription. There are five defined E-boxes in M-cadherin proximal promoter, and reporter result of single E-box mutation showed that E-box 4 is the most important E-box in M-cadherin promoter. Furthermore, it is of interest to investigate whether the cross-talk between E-boxes and MyoD influences MyoD-mediated M-cadherin activation. Recently, our results showed that besides E-box 4, E-box 3 is also an important E-box for MyoD-mediated M-cadherin activation. Moreover, the efficiency of MyoD transactivating M-cadherin may be related to the E-box number presented in promoter region. Once more than three E-boxes were mutated, the ability of MyoD to transactivate M-cadherin transcription would significantly reduce. Indeed, MyoD prefers to form heterodimer with E47 to function in physical condition. Therefore, the dominant positive myogenic factor, MyoD~E47 tethered protein, was used to mimic physical condition of MyoD function. Although MyoD~E47 tethered protein could significantly enhance M-cadherin transcription when compared to MyoD, but it was unable to overcome that more than three E-boxes were required to fully activate M-cadherin transcription. Taken together, the cross-talk between E-boxes and MyoD is certainly present, but detailed mechanism is still waiting to be clarified.
The modulation of PGC-1α transactivational ability by Stra13
Mitochondria-mediated oxidative respiratory is essential for generating high energy ATP for numerous cellular processes. Peroxisome proliferator-activated receptor coactivator 1α (PGC-1α) had been reported to synergize with several nuclear receptors to control mitochondrial biogenesis and function. Besides mitochondria modulation, PGC-1α had been proved to be involved in anti-oxidation and metabolism modulation. Recently, our lab identified a novel interaction between PGC-1α and basic helix-loop-helix (bHLH) repressor, Bhlhe40 or called Stra13. Due to the importance of PGC-1α, it is of interest to investigate the effect of Stra13 on PGC-1α-regulated cellular processes. Results had indicated that altered expression of PGC-1α targets were observed in Stra13 knockdowned C2C12 cells. Moreover, PGC-1α have showed a better transactivation ability in Stra13 knockdowned C2C12 cells. In physiological modulation respect, Stra13 knockdowned C2C12 cells showed a burst of ROS but a reduced mitochondrial membrane potential. Moreover, increased mitochondria content and oxygen consumption implied that mitochondria in Stra13 knockdowned C2C12 cells is likely to be at a more active state. On the other hand, a regressive basal and insulin-induced glucose uptake but an improved palmitic acid oxidation in Stra13 knockdowned C2C12 cells suggests that a switch of nutrient utilization occurred. Consequently, the effect of Stra13 is extensive, and almost all of PGC-1α-involved regulation have been affected and changed. However, it is still unclear that those observations were resulted from relieving Stra13-mediated PGC-1α functional inhibition or just an unspecific effect of loss endogenous Stra13.
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