RasGAP Shields Akt from Deactivating Phosphatases in Fibroblast Growth Factor Signaling but Loses This Ability Once Cleaved by Caspase-3.

Fibroblast growth factor receptors (FGFRs) are involved in proliferative and differentiation physiological responses. Deregulation of FGFR-mediated signaling involving the Ras/PI3K/Akt and the Ras/Raf/ERK MAPK pathways is causally involved in the development of several cancers. The caspase-3/p120 RasGAP module is a stress sensor switch. Under mild stress conditions, RasGAP is cleaved by caspase-3 at position 455. The resulting N-terminal fragment, called fragment N, stimulates anti-death signaling. When caspase-3 activity further increases, fragment N is cleaved at position 157. This generates a fragment, called N2, that no longer protects cells. Here, we investigated in Xenopus oocytes the impact of RasGAP and its fragments on FGF1-mediated signaling during G2/M cell cycle transition. RasGAP used its N-terminal Src homology 2 domain to bind FGFR once stimulated by FGF1, and this was necessary for the recruitment of Akt to the FGFR complex. Fragment N, which did not associate with the FGFR complex, favored FGF1-induced ERK stimulation, leading to accelerated G2/M transition. In contrast, fragment N2 bound the FGFR, and this inhibited mTORC2-dependent Akt Ser-473 phosphorylation and ERK2 phosphorylation but not phosphorylation of Akt on Thr-308. This also blocked cell cycle progression. Inhibition of Akt Ser-473 phosphorylation and entry into G2/M was relieved by PHLPP phosphatase inhibition. Hence, full-length RasGAP favors Akt activity by shielding it from deactivating phosphatases. This shielding was abrogated by fragment N2. These results highlight the role played by RasGAP in FGFR signaling and how graded stress intensities, by generating different RasGAP fragments, can positively or negatively impact this signaling

A specific ChREBP and PPAR alpha cross-talk is required for the glucose-mediated FGF21 response

While the physiological benefits of the fibroblast growth factor 21 (FGF21) hepatokine are documented in response to fasting, little information is available on Fgf21 regulation in a glucose-overload context. We report that peroxisome-proliferator-activated receptor alpha (PPAR alpha), a nuclear receptor of the fasting response, is required with the carbohydrate-sensitive transcription factor carbohydrate-responsive element-binding protein (ChREBP) to balance FGF21 glucose response. Microarray analysis indicated that only a few hepatic genes respond to fasting and glucose similarly to Fgf21. Glucose-challenged Chrebp(-/-) mice exhibit a marked reduction in FGF21 production, a decrease that was rescued by re-expression of an active ChREBP isoform in the liver of Chrebp(-/-) mice. Unexpectedly, carbohydrate challenge of hepatic Ppar alpha knockout mice also demonstrated aPPAR alpha-dependent glucose response for Fgf21 that was associated with an increased sucrose preference. This blunted response was due to decreased Fgf21 promoter accessibility and diminished ChREBP binding onto Fgf21 carbohydrate-responsive element (ChoRE) in hepatocytes lacking PPAR alpha. Our study reports that PPAR alpha is required for the ChREBP-induced glucose response of FGF21

The hepatocyte insulin receptor is required to program the liver clock and rhythmic gene expression.

Liver physiology is circadian and sensitive to feeding and insulin. Food intake regulates insulin secretion and is a dominant signal for the liver clock. However, how much insulin contributes to the effect of feeding on the liver clock and rhythmic gene expression remains to be investigated. Insulin action partly depends on changes in insulin receptor (IR)-dependent gene expression. Here, we use hepatocyte-restricted gene deletion of IR to evaluate its role in the regulation and oscillation of gene expression as well as in the programming of the circadian clock in the adult mouse liver. We find that, in the absence of IR, the rhythmicity of core-clock gene expression is altered in response to day-restricted feeding. This change in core-clock gene expression is associated with defective reprogramming of liver gene expression. Our data show that an intact hepatocyte insulin receptor is required to program the liver clock and associated rhythmic gene expression

Utilização da multimistura durante a lactação e seus efeitos na produção e composição do leite materno de ratas Use of multimixture during lactation and its effects on production and composition of rat milk

A multimistura, composta por farelos, pós de folhas verdes, pós de sementes e pó da casca de ovo, vem sendo amplamente recomendada para aumentar a produção de leite materno, porém sem bases científicas que confirmem sua eficácia. Este estudo objetivou avaliar o desempenho lactacional de ratas alimentadas com dieta suplementada com 2% de multimistura (MM). Foram utilizados ratos fêmeas da linhagem Wistar lactantes com idade entre 90 e 100 dias de vida, divididos nos seguintes grupos (n=12): a) à base da dieta habitual do Estado do Rio de Janeiro (HERJ); b) dieta HERJ suplementada com 2% de multimistura (HERJ+MM); c) à base de caseína, com 12% de proteínas (CAS1); d) à base de caseína, com 20% de proteínas (CAS2). Foram determinados os macronutrientes proteína, lactose e lipídios e a produção de leite. O grupo HERJ+MM apresentou a menor produção de leite (p<0,05) e o menor conteúdo de lactose, quando comparado com os outros. Portanto, conclui-se que a performance lactacional das ratas cuja ração foi suplementada com 2% de multimistura apresentou-se diminuída.<br>The addition of multimixture, composed of bran, green leaves powder, seeds powder and eggshell powder, to the population's diet has been encouraged in Brazil, as a means to increase the production of breast milk, although without scientific bases that confirm its efficacy. The objective of this study was to evaluate the lactation performance of rats receiving ad libitum diet supplemented with 2% of multimixture (MM). Female Wistar-lactating rats of 90 to 100 days of age were divided into the following groups (n=12): a) fed the typical diet of the state of Rio de Janeiro, Brazil (HERJ); b) HERJ diet supplemented with 2% of multimixture (HERJ+MM); c) casein diet, with 12% of proteins (CAS1); d) casein diet, with 20% of proteins (CAS2). Lipid, lactose and protein concentrations and milk production were determined. The HERJ+MM group presented significantly lower milk production (p<0.05) and lower lactose content. In conclusion, there was a decrease in the lactation performance of rats which received diet supplemented with 2% of multimixture