Acquired resistance of lung adenocarcinomas to gefitinib or erlotinib is associated with a second mutation in the EGFR kinase domain

BackgroundLung adenocarcinomas from patients who respond to the tyrosine kinase inhibitors gefitinib (Iressa) or erlotinib (Tarceva) usually harbor somatic gain-of-function mutations in exons encoding the kinase domain of the epidermal growth factor receptor (EGFR). Despite initial responses, patients eventually progress by unknown mechanisms of “acquired” resistance.ConclusionIn patients with tumors bearing gefitinib- or erlotinib-sensitive EGFR mutations, resistant subclones containing an additional EGFR mutation emerge in the presence of drug. This observation should help guide the search for more effective therapy against a specific subset of lung cancers.     

The role of the gel <=> liquid-crystalline phase transition in the lung surfactant cycle

Lipid polymorphism plays an important role in the lung surfactant cycle. A better understanding of the influence of phase transitions on the formation of a lipid film from dispersions of vesicles will help to describe the mechanism of action of lung surfactant. The surface pressure (or tension) of dispersions of DPPC, DMPC, and DPPE unilamellar vesicles was studied as a function of temperature. These aggregates rapidly fuse with a clean air-water interface when the system is at their phase transition temperature (Tm), showing a direct correlation between phase transition and film formation. Based on these results, an explanation on how fluid aggregates in the alveolar subphase can form a rigid monolayer at the alveolar interface is proposed.     

Muscle-specific Drp1 overexpression impairs skeletal muscle growth via translational attenuation

Mitochondrial fission and fusion are essential processes in the maintenance of the skeletal muscle function. The contribution of these processes to muscle development has not been properly investigated in vivo because of the early lethality of the models generated so far. To define the role of mitochondrial fission in muscle development and repair, we have generated a transgenic mouse line that overexpresses the fission-inducing protein Drp1 specifically in skeletal muscle. These mice displayed a drastic impairment in postnatal muscle growth, with reorganisation of the mitochondrial network and reduction of mtDNA quantity, without the deficiency of mitochondrial bioenergetics. Importantly we found that Drp1 overexpression activates the stress-induced PKR/eIF2α/Fgf21 pathway thus leading to an attenuated protein synthesis and downregulation of the growth hormone pathway. These results reveal for the first time how mitochondrial network dynamics influence muscle growth and shed light on aspects of muscle physiology relevant in human muscle pathologies.Skeletal muscle growth and mitochondrial metabolism are intimately linked. In myogenic precursor cells, mitochondrial mass, mtDNA copy number and mitochondrial respiration increase after the onset of myogenic differentiation;^{1, 2} furthermore, postnatal development of fast-twitch muscle is accompanied by an increase in mtDNA copy number³ and muscle regeneration is impaired when mitochondrial protein synthesis is inhibited with chloramphenicol.^{2, 4} These observations suggest that a change in the mitochondrial metabolism is necessary for proper muscle development. During myogenesis and postnatal development, the shape of mitochondria is also remodelled:^{3, 5, 6} in an elegant mouse model with fluorescent mitochondria it was shown that in young mice mitochondria of the extensor digitorum longus (EDL) muscle are shaped as elongated tubules oriented along the long axis of the muscle fibre, whereas in adult mice mitochondria are punctuated and organised into doublets.¹Mitochondrial network morphology is controlled by the balance between fusion and fission. In mammals, three large GTPases are involved in mitochondrial fusion: mitofusins 1 and 2 (Mfn1 and Mfn2) participate in the early steps of mitochondrial outer-membrane fusion, whereas the optic atrophy 1 protein (Opa1) is essential for inner-membrane fusion.⁷ Mitochondrial fission is mediated by the evolutionarily conserved dynamin-related protein 1 (Drp1).⁸ In humans, mutations in Mfn2 and Opa1 cause two neurodegenerative diseases – Charcot–Marie–Tooth type 2 A and dominant optic atrophy, respectively – and a mutation in Drp1 has been linked to neonatal lethality with multisystem failure.^{9, 10, 11} Moreover, Drp1 expression was reported to increase in a model of cachexia¹² and to contribute to muscle insulin resistance in obese and type 2 diabetic mice.^{13, 14}The importance of mitochondrial dynamics in muscle physiology has become increasingly clear. In skeletal muscle, mitochondria undergo fusion to share matrix content in order to support excitation–contraction coupling.¹⁵ The mitochondrial network is remodelled in atrophic conditions, and denervation and expression of fission machinery in adult myofibres is sufficient to cause muscle wasting.¹⁶ Moreover, mice lacking Mfn1 and 2 in fast-twitch muscles exhibit drastic growth defects and muscle atrophy before dying at 6–8 weeks of age.³ Animal models in which mitochondrial fission proteins are manipulated during skeletal muscle development are not yet available, but in vitro data demonstrate that regulation of Drp1 is critical for myogenesis: myoblasts differentiation requires nitric oxide-dependent inhibition of Drp1⁶ and pharmacological inhibition of Drp1 activity impairs myogenic differentiation.¹⁷To explore in vivo the role of Drp1 and mitochondrial shape in the developing muscle, we generated a transgenic mouse line specifically overexpressing Drp1 in skeletal muscle during myogenesis. These mice display strong impairments in mitochondrial network shape and in muscle growth. We show that the mechanism responsible for the growth defect involves inhibition of protein synthesis and activation of the Atf4 pathway.     

Uroguanylin regulates net fluid secretion via the NHE2 isoform of the Na/H+ exchanger in an intestinal cellular model

Uroguanylin (UGN) has been proposed as a key regulator of salt and water intestinal transport. Uroguanylin activates cell-surface guanylate cyclase C receptor (GC-C) and modulates cellular function via cyclic GMP (cGMP), thus increasing electrolyte and net water secretion. It has been suggested that the action of UGN could involve the Na(+)/H(+) exchanger, but the actual contribution of this transporter still remains unclear. The objective of our study was to investigate the putative effects of UGN on some members of the Na(+)/H(+) exchanger family (NHEs), as well as to clarify its consequences on transepithelial fluid flow in T84 cells. In order to do so, transepithelial fluid flow (J(v)) was studied by optic techniques and intracellular pH (pH(i)) was measured with a fluorescence method. Results showed that NHE2 is found at the apical membrane and has a major role in Na(+) absorption; NHE1 and NHE4 are localized at the basolateral membrane with a house-keeping role in steady state pH(i). In the assayed conditions, cell exposure to apical UGN increases net secretory J(v), without changing short-circuit currents nor transepithelial resistance, and reduces NHE2 activity. Therefore, at physiological pH, the effect on net J(v) was produced mainly by a reduction in normal Na(+) absorption through NHE2, rather than by the stimulation of electrolyte secretion. Our study shows that the effect of UGN on pH(i) is GC-C/cGMP-mediated and enhanced by sildenafil, thus involving PDE5 enzyme. Additionally, cell exposure to apical UGN results in intracellular alkalinization, probably due to indirect effects on basolateral NHE1 and NHE4, which have a major role in pH(i) regulation.     

Reproductive biology of Abies cephalonica Loudon in Mount Aenos National Park, Cephalonia, Greece

The reproductive biology of the endemic to Greece Abies cephalonica Loudon, including the phenology of the reproductive life cycle, cone production in relation to plant age and the required seed germination conditions, was studied. All individuals growing within 20 permanent plots of 100 m² each established in 11 different locations covering the entire strictly protected area of Mount Aenos National Park (Cephalonia) were monitored over a period of 4 years. The cones are formed on the upper part of the previous year’s branches, mostly at the upper crown half of the reproductive individuals (over 53 years old). Female flowers are pollinated in spring and cone maturation lasts until the beginning of autumn, when seed dispersal occurs. The annual production of cones per individual varied significantly, revealing masting behavior for this tree. This behavior was also expressed in the number of trees producing cones, as well as the percentage of sound seeds per cone. A significant difference in the mass and the length of the cones between the years of low and high cone production was observed, being higher in the years of massive cone production. Similar germination percentages were observed in full darkness or under “canopy light” and “sun light”, provided that the seeds were previously stratified for 6 weeks. It is concluded that A. cephalonica exhibits plasticity expressed in its reproductive behavior for alternating years of high to low cone production and in its seed germination for an array of habitat light conditions.     

Transdiagnostic psychiatry: a systematic review

The usefulness of current psychiatric classification, which is based on ICD/DSM categorical diagnoses, remains questionable. A promising alternative has been put forward as the “transdiagnostic” approach. This is expected to cut across existing categorical diagnoses and go beyond them, to improve the way we classify and treat mental disorders. This systematic review explores whether self‐defining transdiagnostic research meets such high expectations. A multi‐step Web of Science literature search was performed according to an a priori protocol, to identify all studies that used the word “transdiagnostic” in their title, up to May 5, 2018. Empirical variables which indexed core characteristics were extracted, complemented by a bibliometric and conceptual analysis. A total of 111 studies were included. Most studies were investigating interventions, followed by cognition and psychological processes, and neuroscientific topics. Their samples ranged from 15 to 91,199 (median 148) participants, with a mean age from 10 to more than 60 (median 33) years. There were several methodological inconsistencies relating to the definition of the gold standard (DSM/ICD diagnoses), of the outcome measures and of the transdiagnostic approach. The quality of the studies was generally low and only a few findings were externally replicated. The majority of studies tested transdiagnostic features cutting across different diagnoses, and only a few tested new classification systems beyond the existing diagnoses. About one fifth of the studies were not transdiagnostic at all, because they investigated symptoms and not disorders, a single disorder, or because there was no diagnostic information. The bibliometric analysis revealed that transdiagnostic research largely restricted its focus to anxiety and depressive disorders. The conceptual analysis showed that transdiagnostic research is grounded more on rediscoveries than on true innovations, and that it is affected by some conceptual biases. To date, transdiagnostic approaches have not delivered a credible paradigm shift that can impact classification and clinical care. Practical “TRANSD”iagnostic recommendations are proposed here to guide future research in this field.     

Comparative assessment of fluorescent transgene methods for quantitative imaging in human cells

Fluorescence tagging of proteins is a widely used tool to study protein function and dynamics in live cells. However, the extent to which different mammalian transgene methods faithfully report on the properties of endogenous proteins has not been studied comparatively. Here we use quantitative live-cell imaging and single-molecule spectroscopy to analyze how different transgene systems affect imaging of the functional properties of the mitotic kinase Aurora B. We show that the transgene method fundamentally influences level and variability of expression and can severely compromise the ability to report on endogenous binding and localization parameters, providing a guide for quantitative imaging studies in mammalian cells.