Sumoylation of the net inhibitory domain (NID) is stimulated by PIAS1 and has a negative effect on the transcriptional activity of Net.

Net (Elk-3, Sap-2, Erp) and the related ternary complex factors Elk-1 and Sap-1 are effectors of multiple signalling pathways at the transcriptional level and play a key role in the dynamic regulation of gene expression. Net is distinct from Elk-1 and Sap-1, in that it is a strong repressor of transcription that is converted to an activator by the Ras/Erk signalling pathway. Two autonomous repression domains of Net, the NID and the CID, mediate repression. We have previously shown that the co-repressor CtBP is implicated in repression by the CID. In this report we show that repression by the NID involves a different pathway, sumoylation by Ubc9 and PIAS1. PIAS1 interacts with the NID in the two-hybrid assay and in vitro. Ubc9 and PIAS1 stimulate sumoylation in vivo of lysine 162 in the NID. Sumoylation of lysine 162 increases repression by Net and decreases the positive activity of Net. These results increase our understanding of how one of the ternary complex factors regulates transcription, and contribute to the understanding of how different domains of a transcription factor participate in the complexity of regulation of gene expression.

Idebenone delays the onset of cardiac functional alteration without correction of Fe-S enzymes deficit in a mouse model for Friedreich ataxia.

Friedreich ataxia (FRDA), a progressive neurodegenerative disorder associated with cardiomyopathy, is caused by severely reduced frataxin, a mitochondrial protein involved in Fe-S cluster assembly. We have recently generated mouse models that reproduce important progressive pathological and biochemical features of the human disease. Our frataxin-deficient mouse models initially demonstrate time-dependent intramitochondrial iron accumulation, which occurs after onset of the pathology and after inactivation of the Fe-S dependent enzymes. Here, we report a more detailed pathophysiological characterization of our mouse model with isolated cardiac disease by echocardiographic, biochemical and histological studies and its use for placebo-controlled therapeutic trial with Idebenone. The Fe-S enzyme deficiency occurs at 4 weeks of age, prior to cardiac dilatation and concomitant development of left ventricular hypertrophy, while the mitochondrial iron accumulation occurs at a terminal stage. From 7 weeks onward, Fe-S enzyme activities are strongly decreased and are associated with lower levels of oxidative stress markers, as a consequence of reduced respiratory chain activity. Furthermore, we demonstrate that the antioxidant Idebenone delays the cardiac disease onset, progression and death of frataxin deficient animals by 1 week, but does not correct the Fe-S enzyme deficiency. Our results support the view that frataxin is a necessary, albeit non-essential, component of the Fe-S cluster biogenesis, and indicate that Idebenone acts downstream of the primary Fe-S enzyme deficit. Furthermore, our results demonstrate that Idebenone is cardioprotective even in the context of a complete lack of frataxin, which further supports its utilization for the treatment of FRDA.

Sp100 interacts with ETS-1 and stimulates its transcriptional activity.

The cell nucleus is highly organized into distinct domains that spatially separate physiological processes. One of these domains, the Sp100-promyelocytic leukemia protein nuclear body (NB), is implicated in pathological processes, such as cancer and viral infection, yet its functions remain poorly understood. We show here that Sp100 interacts physically and functionally with ETS-1 and that NB morphology is affected by ETS-1. ETS-1 is a member of the ets family of transcription factors, which are key mediators of physiological and pathological processes. We have found that Sp100 interacts with two regions of ETS-1 (domains A+B and D+E+F). ETS-1 alters NBs while remaining localized throughout the nucleus, apparently by recruitment of the core component Sp100 away from the NBs. Sp100 strongly increases ETS-1 activation of natural and ets-focused promoters, through a mechanism involving the activation (C) domain of ETS-1 in addition to the interaction domains. Sp100 acts as a novel coactivator that potentiates the activator function of ETS-1. Our results provide an important new connection between nuclear structures and an important regulator of gene expression.