SUMMARY Hepatic glucose release into the circulation is vital for brain function and survival during periods of fasting and is modulated by an array of hormones that precisely regulate plasma glucose levels. We have identified a fasting-induced protein hormone that modulates hepatic glucose release. It is the C-terminal cleavage product of profibrillin, and we name it Asprosin. Asprosin is secreted by white adipose, circulates at nanomolar levels, and is recruited to the liver, where it activates the G protein-cAMP-PKA pathway, resulting in rapid glucose release into the circulation. Humans and mice with insulin resistance show pathologically elevated plasma asprosin, and its loss of function via immunologic or genetic means has a profound glucose- and insulin-lowering effect secondary to reduced hepatic glucose release. Asprosin represents a glucogenic protein hormone, and therapeutically targeting it may be beneficial in type II diabetes and metabolic syndrome.

SUMMARY Besides circadian rhythms, oscillations cycling with a 12h period exist. However, the prevalence, origin, regulation and function of mammalian 12h rhythms remain elusive. Utilizing an unbiased mathematical approach identifying all superimposed oscillations, we uncovered prevalent 12h gene expression and metabolic rhythms in mouse liver, coupled with a physiological 12h unfolded protein response oscillation. The mammalian 12h rhythm is cell-autonomous, driven by a dedicated 12h pacemaker distinct from the circadian clock and can be entrained in vitro by metabolic and ER stress cues. Mechanistically, we identified XBP1s as a transcriptional regulator of the mammalian 12h-clock. Down-regulation of the 12h gene expression strongly correlates with human hepatic steatosis and steatohepatitis, implying its importance in maintaining metabolic homeostasis. The mammalian 12h rhythm of gene expression also is conserved in nematodes and crustaceans, indicating an ancient origin of the 12h-clock. Our work sheds new light on how perturbed biological rhythms contribute to human disease.

Hepatic glucose production is critical for basal brain function and survival when dietary glucose is unavailable. Glucose-6-phosphatase (G6Pase) is an essential, rate-limiting enzyme that serves as a terminal gatekeeper for hepatic glucose release into the plasma. Mutations in G6Pase result in Von Gierke's disease (glycogen storage disease–1a), a potentially fatal genetic disorder. We have identified the transcriptional coactivator SRC-2 as a regulator of fasting hepatic glucose release, a function that SRC-2 performs by controlling the expression of hepatic G6Pase. SRC-2 modulates G6Pase expression directly by acting as a coactivator with the orphan nuclear receptor RORα. In addition, SRC-2 ablation, in both a whole-body and liver-specific manner, resulted in a Von Gierke's disease phenotype in mice. Our results position SRC-2 as a critical regulator of mammalian glucose production.

Nonalcoholic fatty liver disease (NAFLD) is a growing epidemic paralleling the increase in obesity and diabetes mellitus seen in Western diet-consuming countries. As NAFLD can lead to life-threatening conditions such as cirrhosis and hepatocellular carcinoma (HCC), an understanding of factors that trigger its development and pathological progression is needed. Although by definition this disease is not associated with alcohol consumption, exposure to environmental agents that have been linked to other diseases might have a role in the development of NAFLD. Here, we focus on one class of these agents, endocrine-disrupting chemicals (EDCs), and their potential to influence the initiation and progression of a cascade of pathological conditions associated with fatty liver. Experimental studies have revealed several potential mechanisms by which EDC exposures might contribute to disease pathogenesis, including modulation of nuclear hormone receptor (NR) function and alteration of the epigenome. However, many questions remain to be addressed about the causal link between acute and chronic EDC exposure and the development of NAFLD in humans. Future studies that address these questions hold promise not only for understanding the linkage between EDC exposure and liver disease, but for elucidating the molecular mechanisms underpinning NAFLD and the development of new prevention and treatment opportunities.

The three members of the p160 family of steroid receptor coactivators (SRC-1, SRC-2, and SRC-3) steer the functional output of numerous genetic programs and serve as pleiotropic rheostats for diverse physiological processes. Since their discovery ϳ15 years ago, the extraordinary sum of examination of SRC function has shaped the foundation of our knowledge for the now 350؉ coregulators that have been identified to date. In this perspective, we retrace our steps into the field of coregulators and provide a summary of selected seminal work that helped define the SRCs as masters of systems biology. A Stroll Down Memory LaneMore than half a century ago, Britten and Davidson first proposed their theory of master genes (1). Since then, countless attempts have been made to crown genes as master regulators. However, the criteria set forth by Britten and Davidson, that a true master gene integrates the transcription of many "producer" genes in response to a single molecular event, has been satisfied only by an incredibly finite set of genes. Now, more than a decade and a half after the discovery of the first steroid receptor coactivator (SRC), 2 we believe that the genes that encode the coregulators have evolved as bona fide master genes of physiology in eukaryotes.Our own journey into the field of coregulators began in the early 1970s, when we discovered that nuclear receptors (NRs) bound to nuclear DNA as a complex associated with proteins that we coined "acceptor proteins" (2). These acceptor proteins were first identified in non-histone nuclear fractions, and we originally viewed them as simple adapter molecules that did not bind ligand themselves but rather accepted the NR-ligand complex into chromatin and facilitated the downstream transcriptional actions of the receptor. At the time, we hypothesized there were a limited number of these adapter proteins that served to bridge the basal transcriptional machinery to the liganded receptor. Our extensive efforts to purify an acceptor protein via size and charge exclusion chromatography produced numerous perplexing peaks, and we eventually abandoned the project. Around this time, the laboratory of Murray and Towle made similar observations working with the thyroid receptor, which associated differentially with proteins from tissue nuclear extracts in response to ligand (3). Little did we know at the time that, taken together, these complex observations would come to represent the vast heterogeneity of NR coregulators that are now known to exist in mammalian cells.Our contributions to the field of coregulator function and NR biology are undoubtedly built upon the efforts and findings of numerous laboratories. Here, we provide our account of our work on the SRC family of coregulators that shaped our thinking and honed our understanding of coregulator function in general. From the mid-80s to the early 90s, our laboratory continued to work on NR action in cell-free transcription systems. We were consistently forced to revisit these elusive acceptor proteins when we realized t...

Calcium (Ca2+) is an essential ligand that binds its primary intracellular receptor Calmodulin (CaM) to trigger a variety of downstream processes and pathways. Central to the actions of Ca2+/CaM is the activation of a highly conserved Ca2+/CaM kinase (CaMK) cascade, which amplifies Ca2+ signals through a series of subsequent phosphorylation events. Proper regulation of Ca2+ flux is necessary for whole-body metabolism and disruption of Ca2+ homeostasis has been linked to a variety of metabolic diseases. Herein, we provide a synthesis of recent advances that highlight the roles of the Ca2+/CaM kinase axis in key metabolic tissues. An appreciation of this information is critical in order to understand the mechanisms by which Ca2+/CaM-dependent signaling contributes to metabolic homeostasis and disease.

Hepatic cancer is one of the most lethal cancers worldwide. Here, we report that the expression of Ca2+/calmodulin-dependent protein kinase kinase 2 (CaMKK2) is significantly up-regulated in hepatocellular carcinoma (HCC) and negatively correlated with HCC patient survival. The CaMKK2 protein is highly expressed in all eight hepatic cancer cell lines evaluated and is markedly up-regulated relative to normal primary hepatocytes. Loss of CaMKK2 function is sufficient to inhibit liver cancer cell growth, and the growth defect resulting from loss of CaMKK2 can be rescued by ectopic expression of wild-type CaMKK2 but not by kinase-inactive mutants. Cellular ablation of CaMKK2 using RNA interference yields a gene signature that correlates with improvement in HCC patient survival, and ablation or pharmacological inhibition of CaMKK2 with STO-609 impairs tumorigenicity of liver cancer cells in vivo. Moreover, CaMKK2 expression is up-regulated in a time-dependent manner in a carcinogen-induced HCC mouse model, and STO-609 treatment regresses hepatic tumor burden in this model. Mechanistically, CaMKK2 signals through Ca2+/calmodulin-dependent protein kinase 4 (CaMKIV) to control liver cancer cell growth. Further analysis revealed that CaMKK2 serves as a scaffold to assemble CaMKIV with key components of the mammalian target of rapamycin/ribosomal protein S6 kinase, 70 kDa, pathway and thereby stimulate protein synthesis through protein phosphorylation. Conclusion The CaMKK2/CaMKIV relay is an upstream regulator of the oncogenic mammalian target of rapamycin/ribosomal protein S6 kinase, 70 kDa, pathway, and the importance of this CaMKK2/CaM-KIV axis in HCC growth is confirmed by the potent growth inhibitory effects of genetically or pharmacologically decreasing CaMKK2 activity; collectively, these findings suggest that CaMKK2 and CaMKIV may represent potential targets for hepatic cancer.

Our group recently characterized a cell-autonomous mammalian 12-h clock independent from the circadian clock, but its function and mechanism of regulation remain poorly understood. Here, we show that in mouse liver, transcriptional regulation significantly contributes to the establishment of 12-h rhythms of mRNA expression in a manner dependent on Spliced Form of X-box Binding Protein 1 (XBP1s). Mechanistically, the motif stringency of XBP1s promoter binding sites dictates XBP1s's ability to drive 12-h rhythms of nascent mRNA transcription at dawn and dusk, which are enriched for basal transcription regulation, mRNA processing and export, ribosome biogenesis, translation initiation, and protein processing/sorting in the Endoplasmic Reticulum (ER)-Golgi in a temporal order consistent with the progressive molecular processing sequence described by the central dogma information flow (CEDIF). We further identified GA-binding proteins (GABPs) as putative novel transcriptional regulators driving 12-h rhythms of gene expression with more diverse phases. These 12-h rhythms of gene expression are cell autonomous and evolutionarily conserved in marine animals possessing a circatidal clock. Our results demonstrate an evolutionarily conserved, intricate network of transcriptional control of the mammalian 12-h clock that mediates diverse biological pathways. We speculate that the 12-h clock is coopted to accommodate elevated gene expression and processing in mammals at the two rush hours, with the particular genes processed at each rush hour regulated by the circadian and/or tissue-specific pathways.