A vertebrate securin (vSecurin) was identified on the basis of its biochemical analogy to the Pds1p protein of budding yeast and the Cut2p protein of fission yeast. The vSecurin protein bound to a vertebrate homolog of yeast separins Esp1p and Cut1p and was degraded by proteolysis mediated by an anaphase-promoting complex in a manner dependent on a destruction motif. Furthermore, expression of a stable Xenopus securin mutant protein blocked sister-chromatid separation but did not block the embryonic cell cycle. The vSecurin proteins share extensive sequence similarity with each other but show no sequence similarity to either of their yeast counterparts. Human securin is identical to the product of the gene called pituitary tumor-transforming gene (PTTG), which is overexpressed in some tumors and exhibits transforming activity in NIH 3T3 cells. The oncogenic nature of increased expression of vSecurin may result from chromosome gain or loss, produced by errors in chromatid separation.

Circadian clock genes are regulated by glucocorticoids; however, whether this regulation is a direct or secondary effect and the physiological consequences of this regulation were unknown. Here, we identified glucocorticoid response elements (GREs) at multiple clock genes and showed that 3 were directly regulated by the glucocorticoid receptor. We determined that a GRE within the core clock gene Per2 was continuously occupied during rhythmic expression and essential for glucocorticoid regulation of that gene in vivo. We further demonstrated that mice with a genomic deletion spanning this GRE expressed elevated leptin levels and were protected from glucose intolerance and insulin resistance on glucocorticoid treatment but not from muscle wasting. We conclude that Per2 is an integral component of a particular glucocorticoid regulatory pathway and that glucocorticoid regulation of the peripheral clock is selectively required for some actions of glucocorticoids.circadian rhythm ͉ diabetes ͉ nuclear receptors ͉ metabolic syndrome

Individual metazoan transcription factors (TFs) regulate distinct sets of genes depending on cell type and developmental or physiological context. The precise mechanisms by which regulatory information from ligands, genomic sequence elements, co-factors, and post-translational modifications are integrated by TFs remain challenging questions. Here, we examine how a single regulatory input, sumoylation, differentially modulates the activity of a conserved C. elegans nuclear hormone receptor, NHR-25, in different cell types. Through a combination of yeast two-hybrid analysis and in vitro biochemistry we identified the single C. elegans SUMO (SMO-1) as an NHR-25 interacting protein, and showed that NHR-25 is sumoylated on at least four lysines. Some of the sumoylation acceptor sites are in common with those of the NHR-25 mammalian orthologs SF-1 and LRH-1, demonstrating that sumoylation has been strongly conserved within the NR5A family. We showed that NHR-25 bound canonical SF-1 binding sequences to regulate transcription, and that NHR-25 activity was enhanced in vivo upon loss of sumoylation. Knockdown of smo-1 mimicked NHR-25 overexpression with respect to maintenance of the 3° cell fate in vulval precursor cells (VPCs) during development. Importantly, however, overexpression of unsumoylatable alleles of NHR-25 revealed that NHR-25 sumoylation is critical for maintaining 3° cell fate. Moreover, SUMO also conferred formation of a developmental time-dependent NHR-25 concentration gradient across the VPCs. That is, accumulation of GFP-tagged NHR-25 was uniform across VPCs at the beginning of development, but as cells began dividing, a smo-1-dependent NHR-25 gradient formed with highest levels in 1° fated VPCs, intermediate levels in 2° fated VPCs, and low levels in 3° fated VPCs. We conclude that sumoylation operates at multiple levels to affect NHR-25 activity in a highly coordinated spatial and temporal manner.

Metazoan transcription factors control distinct networks of genes in specific tissues, yet understanding how these networks are integrated into physiology, development, and homeostasis remains challenging. Inactivation of the nuclear hormone receptor nhr-25 ameliorates developmental and metabolic phenotypes associated with loss of function of an acyl-CoA synthetase gene, acs-3. ACS-3 activity prevents aberrantly high NHR-25 activity. Here, we investigated this relationship further by examining gene expression patterns following acs-3 and nhr-25 inactivation. Unexpectedly, we found that the acs-3 mutation or nhr-25 RNAi resulted in similar transcriptomes with enrichment in innate immunity and stress response gene expression. Mutants of either gene exhibited distinct sensitivities to pathogens and environmental stresses. Only nhr-25 was required for wild-type levels of resistance to the bacterial pathogen P. aeruginosa and only acs-3 was required for wild-type levels of resistance to osmotic stress and the oxidative stress generator, juglone. Inactivation of either acs-3 or nhr-25 compromised lifespan and resistance to the fungal pathogen D. coniospora. Double mutants exhibited more severe defects in the lifespan and P. aeruginosa assays, but were similar to the single mutants in other assays. Finally, acs-3 mutants displayed defects in their epidermal surface barrier, potentially accounting for the observed sensitivities. Together, these data indicate that inactivation of either acs-3 or nhr-25 causes stress sensitivity and increased expression of innate immunity/stress genes, most likely by different mechanisms. Elevated expression of these immune/stress genes appears to abrogate the transcriptional signatures relevant to metabolism and development.