Metformin, the most prescribed antidiabetic medicine, has shown other benefits such as anti-ageing and anticancer effects1–4. For clinical doses of metformin, AMP-activated protein kinase (AMPK) has a major role in its mechanism of action4,5; however, the direct molecular target of metformin remains unknown. Here we show that clinically relevant concentrations of metformin inhibit the lysosomal proton pump v-ATPase, which is a central node for AMPK activation following glucose starvation6. We synthesize a photoactive metformin probe and identify PEN2, a subunit of γ-secretase7, as a binding partner of metformin with a dissociation constant at micromolar levels. Metformin-bound PEN2 forms a complex with ATP6AP1, a subunit of the v-ATPase8, which leads to the inhibition of v-ATPase and the activation of AMPK without effects on cellular AMP levels. Knockout of PEN2 or re-introduction of a PEN2 mutant that does not bind ATP6AP1 blunts AMPK activation. In vivo, liver-specific knockout of Pen2 abolishes metformin-mediated reduction of hepatic fat content, whereas intestine-specific knockout of Pen2 impairs its glucose-lowering effects. Furthermore, knockdown of pen-2 in Caenorhabditis elegans abrogates metformin-induced extension of lifespan. Together, these findings reveal that metformin binds PEN2 and initiates a signalling route that intersects, through ATP6AP1, the lysosomal glucose-sensing pathway for AMPK activation. This ensures that metformin exerts its therapeutic benefits in patients without substantial adverse effects.

Curcumin, an active ingredient from the rhizome of the plant, Curcuma longa, has antioxidant, anti-inflammatory and anti-cancer activities. It has recently been demonstrated that the chemopreventive activities of curcumin might be due to its ability to inhibit cell growth and induce apoptosis. In the present study, we have investigated the effects of curcumin on growth and apoptosis in the human ovarian cancer cell line Ho-8910 by MTT assay, fluorescence microscopy, flow cytometry and Western blotting. Our data revealed that curcumin could significantly inhibit the growth and induce apoptosis in Ho-8910 cells. A decrease in expression of Bcl-2, Bcl-X(L) and pro-caspase-3 was observed after exposure to 40 microM curcumin, while the levels of p53 and Bax were increased in the curcumin-treated cells. These activities may contribute to the anticarcinogenic action of curcumin.

Autophagy is linked to cell death, yet the associated mechanisms are largely undercharacterized. We discovered that melanoma, which is generally resistant to drug-induced apoptosis, can undergo autophagic cell death with the participation of orphan nuclear receptor TR3. A sequence of molecular events leading to cellular demise is launched by a specific chemical compound, 1-(3,4,5-trihydroxyphenyl)nonan-1-one, newly acquired from screening a library of TR3-targeting compounds. The autophagic cascade comprises TR3 translocation to mitochondria through interaction with the mitochondrial outer membrane protein Nix, crossing into the mitochondrial inner membrane through Tom40 and Tom70 channel proteins, dissipation of mitochondrial membrane potential by the permeability transition pore complex ANT1-VDAC1 and induction of autophagy. This process leads to excessive mitochondria clearance and irreversible cell death. It implicates a new approach to melanoma therapy through activation of a mitochondrial signaling pathway that integrates a nuclear receptor with autophagy for cell death.

Highlights d HCC-cell-derived ectosomal PKM2 induces monocyte-tomacrophage differentiation d Remodeling tumor microenvironment by ectosomal PKM2 promotes HCC progression d Sumoylation facilitates PKM2 sorting into ectosomes in an ARRDC1-dependent manner d Macrophage-secreted CCL1 reinforces PKM2 ectosomal excretion in a feedforward loop

Demyelinating diseases, such as multiple sclerosis, are known to result from acute or chronic injury to the myelin sheath and inadequate remyelination; however, the underlying molecular mechanisms remain unclear. Here, we performed genome occupancy analysis by chromatin immunoprecipitation sequencing in oligodendrocytes in response to lysolecithin-induced injury and found that Olig2 and its downstream target Gpr17 are critical factors in regulating oligodendrocyte survival. After injury to oligodendrocytes, Olig2 was significantly upregulated and transcriptionally targeted the Gpr17 locus. Gpr17 activation inhibited oligodendrocyte survival by reducing the intracellular cAMP level and inducing expression of the pro-apoptotic gene Xaf1. The protein kinase A signaling pathway and the transcription factor c-Fos mediated the regulatory effects of Gpr17 in oligodendrocytes. We showed that Gpr17 inhibition elevated Epac1 expression and promoted oligodendrocyte differentiation. The loss of Gpr17, either globally or specifically in oligodendrocytes, led to an earlier onset of remyelination after myelin injury in mice. Similarly, pharmacological inhibition of Gpr17 with pranlukast promoted remyelination. Our findings indicate that Gpr17, an Olig2 transcriptional target, is activated after injury to oligodendrocytes and that targeted inhibition of Gpr17 promotes oligodendrocyte remyelination.

Genistein is a major isoflavonoid in dietary soybean, commonly consumed in Asia. Genistein exerts inhibitory effects on the proliferation of various cancer cells and plays an important role in cancer prevention. However, the molecular and cellular mechanisms of genistein on human ovarian cancer cells are still little known. We show that exposure of human ovarian cancer HO-8910 cells to genistein induces DNA damage, and triggers G2/M phase arrest and apoptosis. Furthermore, we also found that checkpoint proteins ATM and ATR are phosphorylated and activated in the cells treated with genistein. It is also shown that genistein increases the phosphorylation and activation of Chk1 and Chk2, which results in the phosphorylation and inactivation of phosphatases Cdc25C and Cdc25A, and thereby the phosphorylation and inactivation of Cdc2 which arrests cells in G2/M phase. Moreover, genistein enhances the phosphorylation and activation of p53, while decreases the ratio of Bcl-2/Bax and Bcl-xL/Bax and the level of phosphorylated Akt, which result in cells undergoing apoptosis. These results demonstrate that genistein-activated ATM-Chk2-Cdc25 and ATR-Chk1-Cdc25 DNA damage checkpoint pathways can arrest ovarian cancer cells in G2/M phase, and induce apoptosis while the cellular DNA damage is too serious to be repaired. Thus, the antiproliferative, DNA damage-inducing and pro-apoptotic activities of genistein are probably responsible for its genotoxic effects on human ovarian cancer HO-8910 cells.

No abstract

Morphogenesis of many protozoans depends on a polarized establishment of cytoskeletal structures. In malaria‐causing parasites, this can be observed when a round zygote develops into an elongated motile ookinete within the mosquito stomach. This morphogenesis is mediated by the pellicle cytoskeletal structures, including the inner membrane complex (IMC) and the underlying subpellicular microtubules (SPMs). How the parasite maintains the IMC‐SPM connection and establishes a dome‐like structure of SPM to support cell elongation is unclear. Here, we show that palmitoylation of N‐terminal cysteines of two IMC proteins (ISP1/ISP3) regulates the IMC localization of ISP1/ISP3 and zygote‐to‐ookinete differentiation. Palmitoylation of ISP1/ISP3 is catalyzed by an IMC‐residing palmitoyl‐S‐acyl‐transferase (PAT) DHHC2. Surprisingly, DHHC2 undergoes self‐palmitoylation at C‐terminal cysteines via its PAT activity, which controls DHHC2 localization in IMC after zygote formation. IMC‐anchored ISP1 and ISP3 interact with microtubule component β‐tubulin, serving as tethers to maintain the proper structure of SPM during zygote elongation. This study identifies the first PAT–substrate pair in malaria parasites and uncovers a protein palmitoylation cascade regulating microtubule cytoskeleton.