Self-eating to remove cilia roadblock

Autophagy delivers many proteins and cellular components to the lysosome for degradation via selective or nonselective mechanisms. By controlling the stability of defined protein factors, autophagy might regulate cellular processes in a precise and finely-tuned manner. In this study, we demonstrated that autophagy positively regulates the biogenesis of the primary cilium, an antenna-like organelle that senses the environment and transduces signals. Defects in the function or structure of cilia cause a number of human diseases called “ciliopathies.” We found that the autophagosome membrane anchored protein LC3 interacts with OFD1 (oral-facial-digital syndrome 1) and removes it from the centriolar satellite upon serum starvation to initiate primary cilium biogenesis. OFD1 regulation and primary cilium formation are defective in autophagy-deficient cells, and reducing OFD1 protein levels through RNA interference rescues primary cilium formation. More strikingly, knockdown of OFD1 induces primary cilium formation in unstressed cells as well as in a human breast cancer cell that was previously reported to have lost the ability to form primary cilia. These findings therefore suggest an unexpected link among autophagy, ciliogenesis, ciliopathy, and cancers.     

Self-eating and self-killing: crosstalk between autophagy and apoptosis

The functional relationship between apoptosis ('self-killing') and autophagy ('self-eating') is complex in the sense that, under certain circumstances, autophagy constitutes a stress adaptation that avoids cell death (and suppresses apoptosis), whereas in other cellular settings, it constitutes an alternative cell-death pathway. Autophagy and apoptosis may be triggered by common upstream signals, and sometimes this results in combined autophagy and apoptosis; in other instances, the cell switches between the two responses in a mutually exclusive manner. On a molecular level, this means that the apoptotic and autophagic response machineries share common pathways that either link or polarize the cellular responses.     

Self-eating to grow and kill: autophagy in filamentous ascomycetes

Autophagy is a tightly controlled degradation process in which eukaryotic cells digest their own cytoplasm containing protein complexes and organelles in the vacuole or lysosome. Two types of autophagy have been described: macroautophagy and microautophagy. Both types can be further divided into nonselective and selective processes. Molecular analysis of autophagy over the last two decades has mostly used the unicellular ascomycetes Saccharomyces cerevisiae and Pichia pastoris. Genetic analysis in these yeasts has identified 36 autophagy-related (atg) genes; many are conserved in all eukaryotes, including filamentous ascomycetes. However, the autophagic machinery also evolved significant differences in fungi, as a consequence of adaptation to diverse fungal lifestyles. Intensive studies on autophagy in the last few years have shown that autophagy in filamentous fungi is not only involved in nutrient homeostasis but in other cellular processes such as cell differentiation, pathogenicity and secondary metabolite production. This mini-review focuses on the specific roles of autophagy in filamentous fungi.     

Self-eating in skeletal development: Implications for lysosomal storage disorders

Macroautophagy (a.k.a. autophagy) is a cellular process aimed at the recycling of proteins and organelles that is achieved when autophagosomes fuse with lysosomes. Accordingly, lysosomal dysfunctions are often associated with impaired autophagy. We demonstrated that inactivation of the sulfatase modifying factor 1 gene (Sumf1), a gene mutated in Multiple Sulfatase Deficiency (MSD), causes glycosaminoglycans (GAGs) to accumulate in lysosomes, which in turn disrupts autophagy. We utilized a murine model of MSD to study how impairment of this process affects chondrocyte viability and thus skeletal development.     

Tanshinone-induced ERs suppresses IGFII activation to alleviate Ang II-mediated cardiac hypertrophy

Cardiomyopathy involves changes in myocardial ultrastructure and cardiac hypertrophy. Angiotensin II (AngII) has previously been shown to stimulate the expression of IGF-2 and IGF-2R in H9c2 cardiomyoblasts and increase of blood pressure, and cardiac hypertrophy. Estrogen receptors (ERs) exert protective effects, such as anti-hypertrophy in cadiomyocytes. Tanshinone IIA (TSN), a main active ingredient from a Chinese medical herb, Salvia miltiorrhiza Bunge (Danshen), was shown to protect cardiomyocytes hypertrophy by different stress signals. We aimed to investigate whether TSN protected H9c2 cardiomyocytes from AngII-induced activation of IGF-2R pathway and hypertrophy by mediating through ERs. AngII resulted in H9c2 cardiomyoblast hypertrophy and increased inflammatory molecular markers. These were down-regulated by TSN via estrogen receptors. AngII resulted in elevation in MAPKs, IGF-2R and hypertrophic protein markers. These, again, were reduced by addition of the phytoestrogen with activation of ERs. Finally, AngII induced phosphorylation of heat shock factor-1 (HSF1) and decreased sirtuin-1 (SIRT1). In addition, AngII also caused an increase in distribution of IGF-2R molecules on cell membrane. In contrast, TSN reduced HSF1 phosphorylation and cell surface IGF-2R while elevating SIRT1 via ERs. TSN was capable of attenuating AngII-induced IGF-2R pathway and hypertrophy through ERs in H9c2 cardiomyoblast cells.     

脱氢表雄酮经不依赖于雌、雄激素受体的MAPK信号途径抑制成骨细胞凋亡

脱氢表雄酮(DHEA)已成为防治绝经后骨质疏松症(PMO)的新策略,但其调控成骨细胞(OB)凋亡的具体分子机制和信号转导途径尚不清楚。我们通过颅骨酶解法原代培养OB,体外模拟雌激素撤退现象,10-7mol/LDHEA分别作用0h、24h、48h、72h后,RT-PCR分析OB中ERα、ERβ和ARmRNA表达;原代OB去血清进一步培养24h,细胞以雌激素受体(ER)拮抗剂ICI182,780(1μmol/L)、雄激素受体(AR)拮抗剂Flutamide(10μmol/L)或U0126(100μmol/L)预处理后给予系列浓度DHEA(10-10-10-5mol/L)孵育72h,AnnexinV-FITC/PI双标记流式细胞仪分析细胞早期凋亡;原代OB以1μmol/LICI182,780或10μmol/LFlutamide预处理25min后给予不同浓度DHEA孵育10min,Westernblotting分析ERK1/2的磷酸化状态。结果表明OBs经10-7mol/LDHEA体外处理24h、48h、72h后,ERβ和ARmRNA水平升高(分别为P<0.05和P<0.01);而ERαmRNA水平无明显变化。10-9-10-6mol/LDHEA可显著抑制血清饥饿诱导的OBs早期凋亡(分别为P<0.05及P<0.01),该抑制效应可被U0126阻滞,ICI182,780或Flutamide则不能阻滞DHEA对OB的抗凋亡效应;Westernblot也显示ICI182,780或Flutamide都不能有效地阻滞DHEA对OB中ERKs磷酸化的诱导作用。因此可认为DHEA经ER或AR非依赖途径抑制OB凋亡;丝裂原活化蛋白激酶(MAPK)信号途径,磷酸化ERK1/2参与介导这一作用。     

ERs associate with and regulate the production of caveolin: implications for signaling and cellular actions.

Recent evidence supports the existence of a plasma membrane ER. In many cells, E2 activates signal transduction and cell proliferation, but the steroid inhibits signaling and growth in other cells. These effects may be related to interactions of ER with signal-modulating proteins in the membrane. It is also unclear how ER moves to the membrane. Here, we demonstrate ER in purified vesicles from endothelial cell plasma membranes and colocalization of ERalpha with the caveolae structural coat protein, caveolin-1. In human vascular smooth muscle or MCF-7 (human breast cancer) cell membranes, coimmunoprecipitation shows that ER associates with caveolin-1 and -2. Importantly, E2 rapidly and differentially stimulates ER-caveolin association in vascular smooth muscle cells but inhibits association in MCF-7 cells. E2 also stimulates caveolin-1 and -2 protein synthesis and activates a caveolin-1 promoter/luciferase reporter in smooth muscle cells. However, the steroid inhibits caveolin synthesis in MCF-7 cells. To determine a function for caveolin-ER interaction, we expressed caveolin-1 in MCF-7 cells. This stimulated ER translocation to the plasma membrane and also inhibited E2-induced ERK (MAPK) activation. Both functions required the caveolin-1 scaffolding domain. Depending upon the target cell, membrane ERs differentially associate with caveolin, and E2 differentially modulates the synthesis of this signaling-inhibitory scaffold protein. This may explain the discordant signaling and actions of E2 in various cell types. In addition, caveolin-1 is capable of facilitating ER translocation to the membrane.