Caspase-2 promotes cytoskeleton protein degradation during apoptotic cell death.

The caspase family of proteases cleaves large number of proteins resulting in major morphological and biochemical changes during apoptosis. Yet, only a few of these proteins have been reported to selectively cleaved by caspase-2. Numerous observations link caspase-2 to the disruption of the cytoskeleton, although it remains elusive whether any of the cytoskeleton proteins serve as bona fide substrates for caspase-2. Here, we undertook an unbiased proteomic approach to address this question. By differential proteome analysis using two-dimensional gel electrophoresis, we identified four cytoskeleton proteins that were degraded upon treatment with active recombinant caspase-2 in vitro. These proteins were degraded in a caspase-2-dependent manner during apoptosis induced by DNA damage, cytoskeleton disruption or endoplasmic reticulum stress. Hence, degradation of these cytoskeleton proteins was blunted by siRNA targeting of caspase-2 and when caspase-2 activity was pharmacologically inhibited. However, none of these proteins was cleaved directly by caspase-2. Instead, we provide evidence that in cells exposed to apoptotic stimuli, caspase-2 probed these proteins for proteasomal degradation. Taken together, our results depict a new role for caspase-2 in the regulation of the level of cytoskeleton proteins during apoptosis.

Allele-specific programming of Npy and epigenetic effects of physical activity in a genetic model of depression.

Neuropeptide Y (NPY) has been implicated in depression, emotional processing and stress response. Part of this evidence originates from human single-nucleotide polymorphism (SNP) studies. In the present study, we report that a SNP in the rat Npy promoter (C/T; rs105431668) affects in vitro transcription and DNA-protein interactions. Genotyping studies showed that the C-allele of rs105431668 is present in a genetic rat model of depression (Flinders sensitive line; FSL), while the SNP's T-allele is present in its controls (Flinders resistant line; FRL). In vivo experiments revealed binding of a transcription factor (CREB2) and a histone acetyltransferase (Ep300) only at the SNP locus of the FRL. Accordingly, the FRL had increased hippocampal levels of Npy mRNA and H3K18 acetylation; a gene-activating histone modification maintained by Ep300. Next, based on previous studies showing antidepressant-like effects of physical activity in the FSL, we hypothesized that physical activity may affect Npy's epigenetic status. In line with this assumption, physical activity was associated with increased levels of Npy mRNA and H3K18 acetylation. Physical activity was also associated with reduced mRNA levels of a histone deacetylase (Hdac5). Conclusively, the rat rs105431668 appears to be a functional Npy SNP that may underlie depression-like characteristics. In addition, the achieved epigenetic reprogramming of Npy provides molecular support for the putative effectiveness of physical activity as a non-pharmacological antidepressant.

Integration of apoptosis and metabolism.

Apoptotic resistance is a hallmark of human cancers. Recent advances have contributed to our understanding of the molecular mechanisms that intimately integrate cell metabolism and apoptosis. Coordinated activation of the proapoptotic Bcl-2 family and the caspase family during apoptosis often leads to permeabilization of the mitochondrial outer membrane and release of multiple enzymes that normally function in regulating energy production and metabolism. The roles of these metabolic enzymes in promoting caspase activation demonstrate a primordial need to couple apoptotic cell death and metabolic catastrophe during cellular destruction. The Bcl-2 family also directly interacts with the multiple metabolic regulators to protect or promote mitochondrial damage during apoptosis. However, the integration of metabolism and apoptosis is not simply limited to the maintenance of mitochondrial integrity. A recent study demonstrates that the NatA complex, a protein N-α-acetyltransferase complex, is required for DNA damage-mediated apoptosis and suggests that regulation of protein acetylation might provide an important mechanism for regulating apoptotic sensitivity. Since acetyl-CoA (coenzyme A) is a key cofactor for the NatA complex, protein acetylation is subject to the availability of acetyl-CoA and, thus, under metabolic regulation. The revelation that protein N-α-acetylation is regulated by Bcl-xL, a major antiapoptotic mitochondrial protein, demonstrates a mechanism by which metabolism can regulate the activation of multiple key apoptotic factors simultaneously.