mTORC1 Hyperactivity Inhibits Serum Deprivation-Induced Apoptosis via Increased Hexokinase II and GLUT1 Expression,Sustained Mcl-1 Expression,and Glycogen Synthase Kinase 3β Inhibition

The current concept is that Tsc-deficient cells are sensitized to apoptosis due to the inhibition of Akt activity by the negative feedback mechanism induced by the hyperactive mTORC1. Unexpectedly, however, we found that Tsc1/2-deficient cells exhibit increased resistance to serum deprivation-induced apoptosis. mTORC1 hyperactivity contributes to the apoptotic resistance of serum-deprived Tsc1/2-deficient cells in part by increasing the growth factor-independent expression of hexokinase II (HKII) and GLUT1. mTORC1-mediated increase in hypoxia-inducible factor 1α (HIF1α) abundance, which occurs in the absence of serum in normoxic Tsc2-deficient cells, contributes to these changes. Increased HIF1α abundance in these cells is attributed to both an increased level and the sustained translation of HIF1α mRNA. Sustained glycogen synthase kinase 3β inhibition and Mcl-1 expression also contribute to the apoptotic resistance of Tsc2-deficient cells to serum deprivation. The inhibition of mTORC1 activity by either rapamycin or Raptor knockdown cannot resensitize these cells to serum deprivation-induced apoptosis because of elevated Akt activity that is an indirect consequence of mTORC1 inhibition. However, the increased HIF1α abundance and the maintenance of Mcl-1 protein expression in serum-deprived Tsc2^−/− cells are dependent largely on the hyperactive eIF4E in these cells. Consistently, the reduction of eIF4E levels abrogates the resistance of Tsc2^−/− cells to serum deprivation-induced apoptosis.Growth factors are obligatory for the survival of mammalian cells. The evolutionarily conserved kinase Akt has emerged as the predominant and indispensable mediator of the ability of growth factors to promote cell survival in mammalian cells (reviewed in reference 9). Akt promotes cell survival by multiple mechanisms, including key roles in regulating cellular energy metabolism. Akt maintains mitochondrial integrity and inhibits apoptosis at least in part through effects on mitochondrial hexokinases and their functionally coupled facilitated glucose transporters (reviewed in reference 18). One of the most crucial functions of Akt involves the activation of the mammalian target of rapamycin complex 1 (mTORC1), which integrates growth factor signaling with nutritional cues and synchronizes these upstream signals with the downstream stimulation of cell growth and proliferation (reviewed in reference 1). Akt activates mTORC1 in part by inhibiting the heterodimeric tuberous sclerosis complex (Tsc1/Tsc2). Tsc2 (or tuberin) functions as a GTPase-activating protein (GAP) to specifically inhibit the small GTPase Rheb, which activates mTORC1. The formation of a functional heterodimeric complex between Tsc2 and Tsc1 (or hamartin) is required for mTORC1 inhibition. As such, the disruption of the expression or function of either Tsc1 or Tsc2 is sufficient to activate mTORC1. Mammalian cells have evolved a negative feedback mechanism between mTORC1 and Akt to maintain an optimal balance between their activities. When Akt activates mTORC1, it initiates a negative feedback loop that serves to attenuate Akt activity. As such, mTORC1 serves as both an upstream and a downstream effector of Akt signaling. The loss of a functional Tsc1/Tsc2 complex disrupts this delicate balance, resulting in mTORC1 hyperactivity, which greatly reduces Akt activation (reviewed in reference 1). This is relevant to the heritable development of tuberous sclerosis in humans, which is caused by the mutational inactivation of either the TSC1 or TSC2 gene, leading to benign hamartoma formation and growth in a variety of organs (11).It is widely appreciated that low basal Akt activity renders Tsc1/2-deficient cells more sensitive to proapoptotic stimuli (4, 19). Unexpectedly, however, we found that both Tsc1 and Tsc2 null cells exhibit increased apoptotic resistance to growth factor withdrawal despite greatly reduced Akt activity relative to that of their wild-type counterparts. This implies that Tsc1/2 deficiency promotes or unmasks potent antiapoptotic mechanisms that reduce mammalian cell dependence upon growth factors and Akt for survival. Further investigation has uncovered a critical role for mTORC1 in promoting cell survival in the absence of growth factors.Trophic growth factors found in serum play a pivotal role in the cellular uptake and utilization of glucose, and serum withdrawal results in attenuated glucose metabolism. The maintenance of glucose utilization by the overexpression of the rate-limiting glycolytic enzyme hexokinase and its functionally coupled facilitative glucose transporters maintains cell survival in the absence of growth factors (reviewed in reference 18). We found that serum deprivation markedly increased both hexokinase II (HKII) and GLUT1 abundance in Tsc2-deficient cells, and the knockdown of HKII and GLUT1 increased the apoptotic susceptibility of these cells to serum deprivation. The elevated expression of HKII and GLUT1 is mediated by hypoxia-inducible factor 1α (HIF1α) protein, which is markedly induced by mTORC1 in serum-deprived Tsc2^−/− cells.In addition to increased HKII and GLUT1 expression, Tsc2^−/− cells display the sustained inhibition of glycogen synthase kinase 3 (GSK3) activity and stable Mcl-1 abundance following serum withdrawal, which also contribute to their apoptotic resistance under these conditions. Mcl-1 abundance, which normally declines following serum deprivation, is sustained in Tsc2^−/− cells by the constitutive inhibition of GSK3 and the activation of eIF4E.     

Honey as a natural preservative of milk

The anti-bacterial property and preservative nature of honey has been studied by evaluating the role of hydrogen peroxide in these properties, against bacterial strains isolated and identified from pasteurized milk samples. The antibacterial property of honey examined by agar incorporation assay and turbidometry, indicated a concentration dependent inhibition of bacterial growth in all catalase negative strains in comparison with catalase positive strains, highlighting a probable role of hydrogen peroxide. Samples of commercial milk stored at 40C in presence of honey were shown to inhibit opportunistic bacterial growth better compared to samples stored without honey. Due to the bactericidal property of hydrogen peroxide and its preservative nature, honey which is chiefly a combination of various sugars and hydrogen peroxide, can be used a preservative of milk samples.     

Retention of plastic-tipped dart tags in African tigerfish Hydrocynus vittatus

Estimates of tag retention and tagging-related mortality are essential for mark-recapture experiments. Mortality and tag loss were estimated from 15 tigerfish Hydrocynus vittatus marked using Hallmark model PDL plastic-tipped dart tags released into a 1 730 m² pond at Kamutjonga Inland Fisheries Institute, Namibia, and inspected bi-monthly for the presence or absence of tags. No mortality was observed during the experiment. All marked fish had lost their tags after 10 months and 50% tag loss was estimated at 3.9 months. The high tag loss rate indicates that PDL plastic-tipped dart tags are not suitable for long-term studies on this species.     

Inhibition of IRGM establishes a robust antiviral immune state to restrict pathogenic viruses

The type I interferon (IFN) response is the major host arsenal against invading viruses. IRGM is a negative regulator of IFN responses under basal conditions. However, the role of human IRGM during viral infection has remained unclear. In this study, we show that IRGM expression is increased upon viral infection. IFN responses induced by viral PAMPs are negatively regulated by IRGM. Conversely, IRGM depletion results in a robust induction of key viral restriction factors including IFITMs, APOBECs, SAMHD1, tetherin, viperin, and HERC5/6. Additionally, antiviral processes such as MHC‐I antigen presentation and stress granule signaling are enhanced in IRGM‐deficient cells, indicating a robust cell‐intrinsic antiviral immune state. Consistently, IRGM‐depleted cells are resistant to the infection with seven viruses from five different families, including Togaviridae, Herpesviridae, Flaviviverdae, Rhabdoviridae, and Coronaviridae. Moreover, we show that Irgm1 knockout mice are highly resistant to chikungunya virus (CHIKV) infection. Altogether, our work highlights IRGM as a broad therapeutic target to promote defense against a large number of human viruses, including SARS‐CoV‐2, CHIKV, and Zika virus.     

Modulation in light utilization by a microalga Asteracys sp. under mixotrophic growth regimes

Photosynthesis Research - This study is the first to explore the influence of incident light intensity on the photosynthetic responses under mixotrophic growth of microalga Asteracys sp. When grown...     

Natural history of SLC11 genes in vertebrates: tales from the fish world

Background  

The SLC11A1/Nramp1 and SLC11A2/Nramp2 genes belong to the SLC11/Nramp family of transmembrane divalent metal transporters, with SLC11A1 being associated with resistance to pathogens and SLC11A2 involved in intestinal iron uptake and transferrin-bound iron transport. Both members of the SLC11 gene family have been clearly identified in tetrapods; however SLC11A1 has never been documented in teleost fish and is believed to have been lost in this lineage during early vertebrate evolution. In the present work we characterized the SLC11 genes in teleosts and evaluated if the roles attributed to mammalian SLC11 genes are assured by other fish specific SLC11 gene members.     

Recombinant Wolbachia heat shock protein 60 (HSP60) mediated immune responses in patients with lymphatic filariasis

Wolbachia, an endosymbiont present in filarial nematodes, have been implicated in a variety of roles, including the worm development and survival. Elucidation of the role of Wolbachia in filarial nematode biology and pathogenesis has become the focus of many studies and its contribution to parasite survival or immune response is still unclear. Recombinant Wolbachia HSP60 decreases T cell activation and lymphoproliferation in filarial infected people compared to endemic controls as observed by the assessment of T cell activation markers and cytokine responses in the peripheral blood mononuclear cells. Reduced T cell activation may be linked to T regulatory cell activity since it is associated with increased expression of CTLA4 and CD25 on CD4(+) T cells in filarial infected group upon stimulation with recombinant Wolbachia HSP60. In addition, elevated interleukin-10 and TGF-β cytokines corroborate the reduced CD4(+) T cell activation and interferon-γ observed upon recombinant Wolbachia HSP60 stimulation in filarial patients. Hence, these findings indicate that Wolbachia HSP60 may also contribute to the immune modulation seen in filarial patients.     

Effect of stereotactic ablation of the central nucleus of the amygdala on pain sensitivity among rats

The central nucleus of the amygdala (Ce) is a terminal area of the major nociceptive ascending pathway, the spino-(trigemino)-parabrachio-amygdaloid tract. In our study, the Ce was bilaterally electrolytically lesioned in male albino rats. Nociception was assessed by the tail flick latency, which was later compared with the corresponding values in intact and sham-lesioned rats. Stereotactic electrolytic bilateral lesioning of the Ce significantly decreased the sensitivity to pain. In addition, the diurnal variation in the pain sensitivity observed in control animals was noticeably smoothed. Neirofiziologiya/Neurophysiology, Vol. 38, No. 3, pp. 231–234, May–June, 2006.