Autophagy-related Proteins in Genome Stability: Autophagy-Dependent and Independent Actions.

It is emerging that autophagy-related proteins regulate the adaptive response to DNA damage in maintaining genome stability at multiple pathways. Here, we discuss recent insights into how autophagy-related proteins participate in DNA damage repair processes, influence chromosomal instability, and regulate the cell cycle through autophagy-dependent and independent actions. There is increasing awareness of the importance of these pathways mediated by autophagy-related proteins to DNA damage response (DDR), and disturbances in these regulatory connections may be linked to genomic instability participated in various human diseases, such as cancer and aging.

CHK2 Promotes Metabolic Stress-Induced Autophagy through ULK1 Phosphorylation.

Reactive oxygen species (ROS) act as a signaling intermediate to promote cellular adaptation to maintain homeostasis by regulating autophagy during pathophysiological stress. However, the mechanism by which ROS promotes autophagy is still largely unknown. Here, we show that the ATM/CHK2/ULK1 axis initiates autophagy to maintain cellular homeostasis by sensing ROS signaling under metabolic stress. We report that ULK1 is a physiological substrate of CHK2, and that the binding of CHK2 to ULK1 depends on the ROS signal and the phosphorylation of threonine 68 of CHK2 under metabolic stress. Further, CHK2 phosphorylates ULK1 on serine 556, and this phosphorylation is dependent on the ATM/CHK2 signaling pathway. CHK2-mediated phosphorylation of ULK1 promotes autophagic flux and inhibits apoptosis induced by metabolic stress. Taken together, these results demonstrate that the ATM/CHK2/ULK1 axis initiates an autophagic adaptive response by sensing ROS, and it protects cells from metabolic stress-induced cellular damage.

The deacetylation of Foxk2 by Sirt1 reduces chemosensitivity to cisplatin.

In multiple types of cancer, decreased tumour cell apoptosis during chemotherapy is indicative of decreased chemosensitivity. Forkhead box K2 (FOXK2), which is essential for cell fate, regulates cancer cell apoptosis through several post-translational modifications. However, FOXK2 acetylation has not been extensively studied. Here, we evaluated the effects of sirtiun 1 (SIRT1) on FOXK2 deacetylation. Our findings demonstrated that SIRT1 inhibition increased FOXK2-induced chemosensitivity to cisplatin and that K223 in FOXK2 was acetylated. Furthermore, FOXK2 K223 deacetylation reduced chemosensitivity to cisplatin in vitro and in vivo. Mechanistically, FOXK2 was acetylated by the acetyltransferase cAMP response element binding protein and deacetylated by SIRT1. Furthermore, cisplatin attenuated the interaction between FOXK2 and SIRT1. Cisplatin or SIRT1 inhibition enhanced FOXK2 acetylation, thereby reducing the nuclear distribution of FOXK2. Additionally, FOXK2 K223 acetylation significantly affected the expression of cell cycle-related and apoptosis-related genes in cisplatin-stimulated cancer cells, and FOXK2 K223 hyperacetylation promoted mitotic catastrophe, which enhanced chemosensitivity to cisplatin. Overall, our results provided insights into the mechanisms of SIRT1-mediated FOXK2 deacetylation, which was involved in chemosensitivity to cisplatin.

ATM-CHK2-Beclin 1 axis promotes autophagy to maintain ROS homeostasis under oxidative stress.

The homeostatic link between oxidative stress and autophagy plays an important role in cellular responses to a wide variety of physiological and pathological conditions. However, the regulatory pathway and outcomes remain incompletely understood. Here, we show that reactive oxygen species (ROS) function as signaling molecules that regulate autophagy through ataxia-telangiectasia mutated (ATM) and cell cycle checkpoint kinase 2 (CHK2), a DNA damage response (DDR) pathway activated during metabolic and hypoxic stress. We report that CHK2 binds to and phosphorylates Beclin 1 at Ser90/Ser93, thereby impairing Beclin 1-Bcl-2 autophagy-regulatory complex formation in a ROS-dependent fashion. We further demonstrate that CHK2-mediated autophagy has an unexpected role in reducing ROS levels via the removal of damaged mitochondria, which is required for cell survival under stress conditions. Finally, CHK2-/- mice display aggravated infarct phenotypes and reduced Beclin 1 p-Ser90/Ser93 in a cerebral stroke model, suggesting an in vivo role of CHK2-induced autophagy in cell survival. Taken together, these results indicate that the ROS-ATM-CHK2-Beclin 1-autophagy axis serves as a physiological adaptation pathway that protects cells exposed to pathological conditions from stress-induced tissue damage.

Construction of a competing endogenous RNA network using differentially expressed lncRNAs, miRNAs and mRNAs in non­small cell lung cancer.

The competing endogenous RNA (ceRNA) network is crucial for the development and progression of tumors, including non­small cell lung cancer (NSCLC). However, what type of ceRNA network regulates NSCLC has not been clarified. The present study aimed to elucidate the long non­coding RNA (lncRNA)/microRNA (miRNA)/mRNA ceRNA network in NSCLC, particularly for the significance of lncRNAs in NSCLC. NSCLC­specific differentially expressed lncRNAs, miRNAs and mRNAs in the Cancer Genome Atlas (TCGA) were analyzed and their relationship was analyzed by a ceRNA network. Their potential functions of differentially expressed mRNAs were analyzed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). Furthermore, the expression levels of four selected lncRNAs in TCGA were determined and their associated survival of patients was examined. In addition, the expression profiles of these four lncRNAs in 48 NSCLC specimens and cell lines, their cellular distribution and associated clinical parameters were examined. We successfully constructed a ceRNA network, including 113 lncRNAs, 12 miRNAs and 36 mRNAs differentially expressed between NSCLC and non­tumor tissues. LINC00525, MED4­AS1, STEAP2­AS1 and SYNPR­AS1 lncRNAs were selected and validated for their association with the survival of NSCLC patients. The expression of these lncRNAs was upregulated in 48 NSCLC tissues and was varying in NSCLC cells. While LINC00525 was mainly expressed in the cytoplasm, MED4­AS1 was in both the nucleus and cytoplasm of A549 cells. In addition, the expression of LINC00525 was significantly associated with smoking history (P<0.05); MED4­AS1 was significantly associated with women, poor differentiation and lymph node metastasis (P<0.05); STEAP2­AS1 was significantly associated with women (P<0.01); and SYNPR­AS1 was significantly associated with women and adenocarcinoma (P<0.05). These lncRNAs may be valuable biomarkers for prognosis of NSCLC and the ceRNA network may provide new insights in the pathogenesis of NSCLC.

Types and species diversity of Cupressus communities in Southeast Tibet, China.

Cupressus communities are the important parts of natural forests in Southeast Tibet, with significance on plateau biodiversity conservation and ecological security. To clarify their types and plant species diversity, we analyzed species composition and diversity indices, diameter class pattern of constructive species in different communities in Milin County, Lang County and Bomi County, Southeast Tibet. The results showed that Cupressus communities could be classified into four types: C. torulosa-Lonicera lanceolate + Philadelphus tomentosus-Pteris cretica var. nervosa + Digitaria violascens community (Community1), C. gigantea-Desmodium elegans + Sophora moorcroftia-na-Tripogon filiformis + Cymbopogon distans + Orinus thoroldii community (Community2), C. gigantea-Leptodermis purdomii-Chenopodium hybridum + O. thoroldii community (Community 3), and C. gigantea-Ceratostigma minus-A. desertorum + O. thoroldii + Tribulus terrester community (Community 4). Across those four community types, Margalef index, Shannon index, Pielou index and interspecies encounter probability index all ranked with the decreasing order of Community1, Community2, Community 3 and Community 4. Diameter class pattern of the constructive species showed that many young and few middle/old individuals were within the four communities. High mortality rate occurred during the interim period from young to middle age classes. In general, populations of Cupressus plants showed a declining trend.

[Survival state and fruiting characteristics of endangered medicinal plant Sinopodophyllum hexandrum plant in Tibet plateau].

This study was carried out by the methods of typical plots investigation and laboratory test aiming at analyzing the survival state and fruiting characteristics of three Sinopodophyllum hexandrum populations in different environmental habitats. Meanwhile, it could provide scientific basis for enhancing wild population quantity recovery. The results showed that more population quantity grow in the habitats of large-area gap (Population A) and bushes (Population C) with a majority of the young individuals, while the minor-area gap (Population B) was the opposite. The development tendency of S. hexandrum populations would be the recession in the future. Spatial distribution pattern of populations was clumped at small scales but random at large scales. The indexes of population A and C, as fruit size，the quantity and quality of seeds，germ inability，were all superior to those of population B. Comparing the mainly environment factors of three populations, that favorable environmental factors for vegetative and reproductive growth of S. hexandrum populations were found，especially certain lighting intensity and fertile soil. Therefore, the favorable environmental habitats for S. hexandrum individuals growth could be artificial to promote the recovery and quantities of S. hexandrum populations in the future.

[Analysis of photosynthetic characteristics and its influencing factors of medicinal plant Mirabilis himalaica].

To study photosynthetic characteristics and its influencing factors in leaves of medicinal plant Mirabilis himalaica, and provide an evidence for guiding artificial planting and improving the quantity. The light-response and diurnal photosynthesis course of leaves at the booting stages of 1-3 year old M. himalaica were measured with LI-6400 system. The Results showed that the light response curves were fitted well by non rectangle hyperbola equation (R2 > or = 0.98). The values of the maximum photosynthetic rate (Pmax) and light use efficiency of three-year old M. himalaica leaves were higher than those of 1-2 year old individuals. The diurnal variation of net photosynthetic rate (Pn) and stomatal conductance (Gs) of 2-3 year old M. himalaica were typical double-peak curves determinately regulated by stomatal conductance. However, transpiration rate (Tr) of 1-3 year old plants leaves were single-peak curve, which was self-protection of harm reduction caused by the higher temperature at noontime. Correlation analysis showed that the changes between photosynthetic active radiation (PFD), air temperature (T ) and Pn, were significant positive related. Therefore, M. himalaica is a typical sun plant, which should be planted under the sufficient sunshine field and prolong the growing ages suitably in order to improve the yield.

[Distribution pattern of Rhododendron aganniphum var. schizopeplum population at the timberline of Sejila Mountains, Tibet of China].

Rhododendron aganniphum var. schizopeplum grows at the elevation of 4300-4500 m in Sejila Mountains, being a dominant species of shrub layer at the timberline of southeast Tibet. Based on the sampling plot investigation and basal diameter structure analysis, this paper studied the distribution pattern of R. aganniphum var. schizopeplum population at the timberline of Sejila Mountains. With the increase of altitude, the population density of R. aganniphum var. schizopeplum increased, but the population height decreased. At the same altitudes, the population density on the shady slope was larger than that on the sunny slope, while the basal diameter was smaller. On the two slope directions, the distribution of the basal diameter classes of the population appeared as "(see text for symbol)" shape, i. e., middle-aged individuals were more, while seedlings and saplings were relatively less. The intraspecific competition of R. aganniphum var. schizopeplum population was in the form of wave, being stronger on shady slope than on sunny slope, and existing self-thinning.