Downregulation of cardiac lineage protein-1 confers cardioprotection through the upregulation of redox effectors

Functional Interaction between HEXIM and Hedgehog Signaling during Drosophila Wing Development

Studying the dynamic of gene regulatory networks is essential in order to understand the specific signals and factors that govern cell proliferation and differentiation during development. This also has direct implication in human health and cancer biology. The general transcriptional elongation regulator P-TEFb regulates the transcriptional status of many developmental genes. Its biological activity is controlled by an inhibitory complex composed of HEXIM and the 7SK snRNA. Here, we examine the function of HEXIM during Drosophila development. Our key finding is that HEXIM affects the Hedgehog signaling pathway. HEXIM knockdown flies display strong phenotypes and organ failures. In the wing imaginal disc, HEXIM knockdown initially induces ectopic expression of Hedgehog (Hh) and its transcriptional effector Cubitus interuptus (Ci). In turn, deregulated Hedgehog signaling provokes apoptosis, which is continuously compensated by apoptosis-induced cell proliferation. Thus, the HEXIM knockdown mutant phenotype does not result from the apoptotic ablation of imaginal disc; but rather from the failure of dividing cells to commit to a proper developmental program due to Hedgehog signaling defects. Furthermore, we show that ci is a genetic suppressor of hexim. Thus, HEXIM ensures the integrity of Hedgehog signaling in wing imaginal disc, by a yet unknown mechanism. To our knowledge, this is the first time that the physiological function of HEXIM has been addressed in such details in vivo.

Caveolin induces cardioprotection through epigenetic regulation

Lipid rafts represent a sub-compartment of the plasma membrane that co-ordinate and regulate varieties of signalling processes, whereas caveolins are the integral membrane protein of the lipid raft. Recent evidence demonstrated the pivotal role of caveolins in cardioprotection against ischaemic injury, although their mechanism of action is not clear. However, new understanding of epigenetic modification during ischaemia reperfusion suggests additional targeted approaches that have not been explored before. To study the role of caveolin on epigenetic regulation, isolated mouse heart was prepared from wild-type (WT) and caveolin-1 knockout (Cav-1 KO) mouse and preconditioned them with four cyclic episodes of ischaemia/reperfusion followed by 30 min. global ischaemia and 120 min. reperfusion. We found that Cav-1 KO mouse abolished the acetylation of histone (H3 and H4) and increased the methylation of histone in the preconditioned heart. The increased histone methylation was significantly correlated with an increased level of histone methyltranferase G9a protein and increased the level of histone decaetylase (HDAC) activity. Cav-1 KO mouse also decreased the translocation of forkhead transcription factor (FOXO3a) to the nucleus and reduced the induction of the expression of SIRT-1 in the preconditioned heart. Cardioprotective property of Cav-1 was further confirmed by reduced ventricular function, increased cardiomyocyte apoptosis, increased expression of junas kinase (JNK) and Bax and decreased expression of phospho-adenosine monophosphate-activated protein kinase (AMPK), phospho-AKT and B cell lymphoma-2 (Bcl-2) in Cav-1 KO preconditioned heart. The results clearly indicate that Cav-1 induces cardioprotection through epigenetic regulation.