Mainak Ghosh

mTORC2 controls cancer cell survival by modulating gluconeogenesis

For rapid tumor growth, cancer cells often reprogram the cellular metabolic processes to obtain enhanced anabolic precursors and energy. The molecular changes of such metabolic rewiring are far from established. Here we explored the role of mTOR (mechanistic target of rapamycin), which serves as a key regulator of cell growth, proliferation and survival, in the metabolic reprograming of cancer cells. When we inhibited mTOR in human hepatocellular carcinoma (HCC) and renal cell carcinoma (RCC) cells, using pharmacologic inhibitors or by RNA interference, we noticed shuttle of the glycolytic flux to gluconeogenesis pathway along with reduction in cellular proliferation and survival. Augmentation of gluconeogenesis was mechanistically linked to upregulation of the key gluconeogenic enzymes PCK1 and G6PC expressions, enhanced lactate dehydrogenase activity and glucose-derived lipogenesis without causing any attenuation in mitochondrial function. Interestingly, concomitant knocking down of PCK1 and not G6PC along with mTOR pathway could overcome the inhibition of cancer cell proliferation and survival. These observations were validated by identifying distinctive diminution of PCK1 and G6PC expressions in human HCC and RCC transcriptome data. Significant correlation between mTOR-dependent upregulation of PCK1 and cell death in different cancer cell lines further emphasizes the physiological relevance of this pathway. We reveal for the first time that inhibition of mTORC2 and consequent redistribution of glycolytic flux can have a prosurvival role in HCC and RCC cancer cells only in the presence of downregulation of gluconeogenesis pathway genes, thus identifying novel pivots of cancer cell metabolic rewiring and targets for therapy.

Structural characterisation of reaction zone for friction stir welded aluminium-stainless steel joint

Abstract In the present investigation, commercially pure Al has been joined with 304 stainless steel (SS) by friction stir welding. The assembly finds widespread application in the field of cryogenics, nuclear, structural industries and domestic appliances. Microstructural characterisation was carried out using scanning and transmission electron microscopes. It has been found that diffusion of Fe, Cr and Ni is substantial within Al; however, diffusion of Al within 304SS is limited. Owing to interdiffusion of chemical species across the bondline, discrete islands of Fe3Al intermetallic form within the reaction zone. The rubbing action of tool over the butting edge of 304SS removed fine particles from 304SS, which were embedded in the stirring zone of Al matrix. Subsequently, austenite underwent phase transformation to ferrite due to large strain within this grain. Fracture path mainly moves through stirring zone of Al alloy under tensile loading; however, in some places, presence of Fe3Al compound has been also found.

PPARα-ATGL pathway improves muscle mitochondrial metabolism: implication in aging

Adipose triglyceride lipase (ATGL) maintains an optimum mitochondrial function putatively by generating cognate ligands for peroxisome proliferator‐activated receptor α (PPARα), which, together with PPARγ coactivator‐1α (PGC1α), regulate muscle mitochondrial biogenesis. However, the cross‐talk between ATGL and PPARα in skeletal muscle mitochondrial metabolism and its implication in chronological aging is poorly understood. The role of ATGL in muscle mitochondrial metabolism was studied by overexpressing and depleting the geneandstudyingitsdownstreameffect in cultured myotubes and in murine skeletal muscle. We found that PPARα directly induces ATGL expression during myogenesis. Overexpression of ATGL significantly enhanced while depletion of ATGL attenuated mitochondrial oxidative phosphorylation and fatty acid oxidation without alteration in mitochondrial content, and it rendered PPARα and PGC1α redundant in promoting mitochondrial oxidative function. However, ATGL did not alter PPAR‐dependent lipid accumulation and insulin sensitivity. In middleaged rats, ATGL expression was higher and correlated with PPARα expression and sustained fatty acid oxidation in oxidative soleus muscle. Fenofibrate feeding further induced ATGL expression selectively in this muscle compartment. These findings illustrate that PPARα and ATGL constitute a regulatory pathway in skeletal muscle, suggesting their role as a mitochondrial metabolic reserve.—Biswas, D., Ghosh, M., Kumar, S., Chakrabarti, P. PPARα‐ATGL pathway improves muscle mitochondrial metabolism: implication in aging. FASEB J. 30, 3822–3834 (2016) www.fasebj.org

Friction Stir Welding of Stainless Steel to Al Alloy: Effect of Thermal Condition on Weld Nugget Microstructure

Joining of dissimilar materials is always a global challenge. Sometimes it is unavoidable to execute multifarious activities by a single component. In the present investigation, 6061 aluminum alloy and 304 stainless steel were joined by friction stir welding (FSW) at different tool rotational rates. Welded joints were characterized in optical and scanning electron microscopes. Reaction products in the stirring zone (SZ) were confirmed through X-ray diffraction. Joint strength was evaluated by tensile testing. It was found that the increment in average heat input and temperature at the weld nugget (WN) facilitated iron enrichment near the interface. Enhancement in the concentration of iron shifted the nature of intermetallics from the Fe2Al5 to Fe-rich end of the Fe-Al binary phase diagram. The peak microhardness and ultimate tensile strength were found to be maxima at the intermediate tool rotational rate, where Fe3Al and FeAl2 appeared along with Fe2Al5.

X-ray diffraction and Mossbauer spectroscopy studies of cementite dissolution in cold-drawn pearlitic steel

Cementite dissolution in cold-drawn pearlitic steel (0.8 wt.% carbon) wires has been studied by quantitative X-ray diffraction (XRD) and Mössbauer spectroscopy up to drawing strain 1.4. Quantification of cementite-phase fraction by Rietveld analysis has confirmed more than 50% dissolution of cementite phase at drawing strain 1.4. It is found that the lattice parameter of the ferrite phase determined by Rietveld refinement procedure remains nearly unchanged even after cementite dissolution. This confirms that the carbon atoms released after cementite dissolution do not dissolve in the ferrite lattice as Fe-C interstitial solid solution. Detailed analysis of broadening of XRD line profiles for the ferrite phase shows high density of dislocations (∼1015/m2) in the ferrite matrix at drawing strain 1.4. The results suggest a dominant role of ⟨1 1 1⟩ screw dislocations in the cementite dissolution process. Post-deformation heat treatment leads to partial annihilation of dislocations and restoration of cementite phase. Based on these experimental observations, further supplemented by TEM studies, we have suggested an alternative thermodynamic mechanism of the dissolution process.

Liquid phase collagen modified graphene that induces apoptosis

Direct exfoliation of graphite (GR) to collagen modified graphene (G) flakes using acylated collagen has been studied. The chemical structure of collagen (CL) and all liquid exfoliants studied so far have striking similarity, namely, the hydrocarbon chain length, aromatic residues and polarity. Here, CL dispersed in acetic (AA), succinic (SA) and propionic (PA) acid behaves as three different surfactants which have been used to simultaneously exfoliate and disperse nano G platelets to a colloidal form. Transmission electron microscopy micrographs show average dimensions of ∼500 × 200 nm; Moire patterns observed at several places in all the three samples indicate periodic perturbations in the graphitic stacking and selected area electron diffraction confirms graphene formation. AFM images confirmed the same lateral dimensions with an average thickness of 1.2 nm. The Raman spectra revealed strain dependent splitting and a red shift of 2D bands, a maximum in G-PA and minimum in G-AA. X-ray photoelectron spectroscopy showed a decrease of the sp2/sp3 ratio GR post CL interaction indicating an interaction. The zeta potential, fluorescence and luminescence values changed in G, with maximum variation in G-PA; suggesting that CL dispersed in PA is the best. The bioactivity of colloidal G-PA was studied in solid, hematological and neuronal cancer cell lines. It induced reactive oxygen species and cell death in cancer cell lines and altered membrane integrity while sparing normal cells, underscoring its possible utility in cancer therapy.

Ubiquitin Ligase COP1 Controls Hepatic Fat Metabolism by Targeting ATGL for Degradation.

Optimal control of hepatic lipid metabolism is critical for organismal metabolic fitness. In liver, adipose triglyceride lipase (ATGL) serves as a major triacylglycerol (TAG) lipase and controls the bulk of intracellular lipid turnover. However, regulation of ATGL expression and its functional implications in hepatic lipid metabolism, particularly in the context of fatty liver disease, is unclear. We show that E3 ubiquitin ligase COP1 (also known as RFWD2) binds to the consensus VP motif of ATGL and targets it for proteasomal degradation by K-48 linked polyubiquitination, predominantly at the lysine 100 residue. COP1 thus serves as a critical regulator of hepatocyte TAG content, fatty acid mobilization, and oxidation. Moreover, COP1-mediated regulation of hepatic lipid metabolism requires optimum ATGL expression for its metabolic outcome. In vivo, adenovirus-mediated depletion of COP1 ameliorates high-fat diet–induced steatosis in mouse liver and improves liver function. Our study thus provides new insights into the regulation of hepatic lipid metabolism by the ubiquitin-proteasome system and suggests COP1 as a potential therapeutic target for nonalcoholic fatty liver disease.

Interfacial microstructure, shear strength and electrical conductivity of Sn–3˙5Ag–0˙5In/Cu lead free soldered joints

Abstract A Sn–Ag–In ternary alloy was considered as a substitute for eutectic Sn–Pb solder in the joining of electronic components. The microstructure in the diffusion zone of the assemblies was examined by scanning electron microscopy and the presence of Cu6Sn5 intermetallics was confirmed by transmission electron microscopy. The width of brittle intermetallic phases present at the interface was found to control the strength of the solder joint. Sn–3˙5Ag–0˙5In/Cu joints exhibited better mechanical and electrical properties than Sn–37Pb/Cu joints.

Cementite Dissolution in Cold Drawn Pearlitic Steel Wires: Role of Dislocations

Despite numerous investigations in the past, mechanism of cementite dissolution has still remained a matter of debate. The present work investigates cementite dissolution during cold wire drawing of pearlitic steel (~ 0.8wt% carbon) at medium drawing strain (up to true strain 1.4) and the role of dislocations in the ferrite matrix on the dissolution process. Quantitative phase analysis using x-ray diffraction (XRD) confirms more than 50% dissolution of cementite phase at drawing strain ~ 1.4. Detail analysis of the broadening of ferrite diffraction lines confirms presence of strain anisotropy in ferrite due to high density of dislocations (~ 1015m-2) at drawing strain 1.4. The results of the analysis shows that the screw dislocations near the ferrite-cementite interface are predominantly responsible for pulling the carbon atoms out of the cementite phase leading to its dissolution.

Erratum to: Intergranular Corrosion Behavior of 304LN Stainless Steel Heat Treated at 623 K (350 °C)

RAGHUVIR SINGH, Principal Scientist, MUKESH KUMAR, Project Staff, MAINAK GHOSH, Senior Scientist, GAUTAM DAS, Sr. Principal Scientist, and I. CHATTORAJ, Chief Scientist, are with the CSIR-National Metallurgical Laboratory, Jamshedpur 831007, India. Contact e-mail: raghujog@yahoo.co.in; rsr@nmlindia.org P. K. SINGH, Scientific Officer G, is with Reactor Safety Division, Bhabha Atomic Research Centre, Mumbai, India. The online version of the original article can be found under doi:10.1007/s11661-012-1519-4. Article published online April 9, 2013