COT drives resistance to RAF inhibition through MAP kinase pathway reactivation

Oncogenic mutations in the serine/threonine kinase B-RAF (also known as BRAF) are found in 50-70% of malignant melanomas. Pre-clinical studies have demonstrated that the B-RAF(V600E) mutation predicts a dependency on the mitogen-activated protein kinase (MAPK) signalling cascade in melanoma-an observation that has been validated by the success of RAF and MEK inhibitors in clinical trials. However, clinical responses to targeted anticancer therapeutics are frequently confounded by de novo or acquired resistance. Identification of resistance mechanisms in a manner that elucidates alternative 'druggable' targets may inform effective long-term treatment strategies. Here we expressed ～600 kinase and kinase-related open reading frames (ORFs) in parallel to interrogate resistance to a selective RAF kinase inhibitor. We identified MAP3K8 (the gene encoding COT/Tpl2) as a MAPK pathway agonist that drives resistance to RAF inhibition in B-RAF(V600E) cell lines. COT activates ERK primarily through MEK-dependent mechanisms that do not require RAF signalling. Moreover, COT expression is associated with de novo resistance in B-RAF(V600E) cultured cell lines and acquired resistance in melanoma cells and tissue obtained from relapsing patients following treatment with MEK or RAF inhibitors. We further identify combinatorial MAPK pathway inhibition or targeting of COT kinase activity as possible therapeutic strategies for reducing MAPK pathway activation in this setting. Together, these results provide new insights into resistance mechanisms involving the MAPK pathway and articulate an integrative approach through which high-throughput functional screens may inform the development of novel therapeutic strategies.     

Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study

Calorie restriction (CR), a reduction of 10–40% in intake of a nutritious diet, is often reported as the most robust non-genetic mechanism to extend lifespan and healthspan. CR is frequently used as a tool to understand mechanisms behind ageing and age-associated diseases. In addition to and independently of increasing lifespan, CR has been reported to delay or prevent the occurrence of many chronic diseases in a variety of animals. Beneficial effects of CR on outcomes such as immune function, motor coordination and resistance to sarcopenia in rhesus monkeys have recently been reported. We report here that a CR regimen implemented in young and older age rhesus monkeys at the National Institute on Aging (NIA) has not improved survival outcomes. Our findings contrast with an ongoing study at the Wisconsin National Primate Research Center (WNPRC), which reported improved survival associated with 30% CR initiated in adult rhesus monkeys (7–14?years) and a preliminary report with a small number of CR monkeys. Over the years, both NIA and WNPRC have extensively documented beneficial health effects of CR in these two apparently parallel studies. The implications of the WNPRC findings were important as they extended CR findings beyond the laboratory rodent and to a long-lived primate. Our study suggests a separation between health effects, morbidity and mortality, and similar to what has been shown in rodents, study design, husbandry and diet composition may strongly affect the life-prolonging effect of CR in a long-lived nonhuman primate.     

Systematic variation of the stellar initial mass function in early-type galaxies

Much of our knowledge of galaxies comes from analysing the radiation emitted by their stars, which depends on the present number of each type of star in the galaxy. The present number depends on the stellar initial mass function (IMF), which describes the distribution of stellar masses when the population formed, and knowledge of it is critical to almost every aspect of galaxy evolution. More than 50 years after the first IMF determination, no consensus has emerged on whether it is universal among different types of galaxies. Previous studies indicated that the IMF and the dark matter fraction in galaxy centres cannot both be universal, but they could not convincingly discriminate between the two possibilities. Only recently were indications found that massive elliptical galaxies may not have the same IMF as the Milky Way. Here we report a study of the two-dimensional stellar kinematics for the large representative ATLAS(3D) sample of nearby early-type galaxies spanning two orders of magnitude in stellar mass, using detailed dynamical models. We find a strong systematic variation in IMF in early-type galaxies as a function of their stellar mass-to-light ratios, producing differences of a factor of up to three in galactic stellar mass. This implies that a galaxy's IMF depends intimately on the galaxy's formation history.     

Phosphorylation of WAVE1 regulates actin polymerization and dendritic spine morphology

WAVE1--the Wiskott-Aldrich syndrome protein (WASP)--family verprolin homologous protein 1--is a key regulator of actin-dependent morphological processes in mammals, through its ability to activate the actin-related protein (Arp2/3) complex. Here we show that WAVE1 is phosphorylated at multiple sites by cyclin-dependent kinase 5 (Cdk5) both in vitro and in intact mouse neurons. Phosphorylation of WAVE1 by Cdk5 inhibits its ability to regulate Arp2/3 complex-dependent actin polymerization. Loss of WAVE1 function in vivo or in cultured neurons results in a decrease in mature dendritic spines. Expression of a dephosphorylation-mimic mutant of WAVE1 reverses this loss of WAVE1 function in spine morphology, but expression of a phosphorylation-mimic mutant does not. Cyclic AMP (cAMP) signalling reduces phosphorylation of the Cdk5 sites in WAVE1, and increases spine density in a WAVE1-dependent manner. Our data suggest that phosphorylation/dephosphorylation of WAVE1 in neurons has an important role in the formation of the filamentous actin cytoskeleton, and thus in the regulation of dendritic spine morphology.     

铬对萝卜种子发芽与根伸长抑制的生态毒性

针对不同质量浓度的三价铬和六价铬对2种萝卜种子萌发和伸长抑制的生态毒性研究,发现:当三价铬的质量浓度在小于25 mg/L和六价铬的质量浓度在小于8 mg/L时,对种子的萌发有促进作用;高质量浓度2种价态的铬对萝卜种子表现为毒害作用;2种价态铬的质量浓度对数与萝卜根伸长抑制指数之间存在显著的正相关;六价铬毒性大于三价铬。