Nitrogen addition alleviates the adverse effects of drought on plant productivity in a temperate steppe.

Drought and nitrogen enrichment could profoundly affect the productivity of semiarid ecosystems. However, how ecosystem productivity will respond to different drought scenarios, especially with a concurrent increase in nitrogen availability, is still poorly understood. Using data from a 4-year field experiment conducted in a semiarid temperate steppe, we explored the responses of aboveground net primary productivity (ANPP) to different drought scenarios and nitrogen addition, and the underlying mechanisms linking soil properties, plant species richness, functional diversity (community-weighted means of plant traits, functional dispersion) and phylogenetic diversity (net relatedness index) to ANPP. Our results showed that completely excluding precipitation in June (1-month intense drought) and reducing half the precipitation amount from June to August (season-long chronic drought) both significantly reduced ANPP, with the latter having a more negative impact on ANPP. However, reducing half of the precipitation frequency from June to August (precipitation redistribution) had no significant effect on ANPP. Nitrogen addition increased ANPP irrespective of drought scenarios. ANPP was primarily determined by soil moisture and nitrogen availability by regulating the community-weighted means of plant height, rather than other aspects of plant diversity. Our findings suggest that precipitation amount is more important than precipitation redistribution in influencing the productivity of temperate steppe, and nitrogen supply could alleviate the adverse impacts of drought on grassland productivity. Our study advances the mechanistic understanding of how the temperate grassland responds to drought stress, and implies that management strategies to protect tall species in the community would be beneficial for maintaining the productivity and carbon sequestration of grassland ecosystems under climate drought.

Decoupled responses of above- and below-ground beta-diversity to nitrogen enrichment in a typical steppe.

Increased atmospheric nitrogen (N) deposition affects biodiversity in terrestrial ecosystems. However, we do not know whether the effects of N on above-ground plant ß-diversity are coupled with changes occurring in the soil seed bank. We conducted a long-term N-addition experiment in a typical steppe and found that above-ground ß-diversity increased and then decreased with increasing N addition, whereas below-ground ß-diversity decreased linearly. This suggests decoupled dynamics of plant communities and their soil seed bank under N enrichment. Species substitution determined above- and below-ground ß-diversity change via an increasing role of deterministic processes with N addition. These effects were mostly driven by differential responses of the above-ground vegetation and the soil seed bank ß-diversities to N-induced changes in environmental heterogeneity, increased soil inorganic N concentrations and soil acidification. Our findings highlight the importance of considering above- and below-ground processes simultaneously for effectively conserving grassland ecosystems under N enrichment.

Applied phosphorus is maintained in labile and moderately occluded fractions in a typical meadow steppe with the addition of multiple nutrients.

Phosphorus (P) is a limiting nutrient second only to nitrogen (N) in the drylands of the world. Most previous studies have focused on N transformation processes in grassland ecosystems, particularly under artificial fertilization with N and atmospheric N deposition. However, P cycling processes under natural conditions and when P is applied as an inorganic P fertilizer have been understudied. Therefore, it is essential to examine the fate of applied P in grassland ecosystems that have experienced long-term grazing and, under certain circumstances, continuous hay harvest. We conducted a 3-year field experiment with the addition of multiple nutrient elements in a typical meadow steppe to investigate the fate of the applied P in various fractions of P pools in the top soil. We found that the addition of multiple nutrients significantly increased P concentrations in the labile inorganic P (Lab-Pi) and moderately occluded inorganic P (Mod-Pi) fractions but not in the recalcitrant inorganic P (Rec-Pi) fraction. An increase in the concentration of total inorganic P was found only when P and N were applied together. However, the addition of other nutrients did not change P concentrations in any fraction of the mineral soil. The addition of P and N significantly increased the total amount of P taken up by the aboveground plants but had no effect on the levels of organic and microbial P in the soil. Together, our results indicate that the P applied in this grassland ecosystem is taken up by plants, leaving most of the unutilized P as Lab-Pi and Mod-Pi rather than being immobilized in Rec-Pi or by microbial biomass. This implies that the grassland ecosystem that we studied has a relatively low P adsorption capacity, and the application of inorganic P to replenish soil P deficiency in degraded grasslands due to long-term grazing of livestock or continuous harvest of forage in the region could be a practical management strategy to maintain soil P fertility.

Nitrogen addition and mowing alter drought resistance and recovery of grassland communities.

Nitrogen enrichment and land use are known to influence various ecosystems, but how these anthropogenic changes influence community and ecosystem responses to disturbance remains poorly understood. Here we investigated the effects of increased nitrogen input and mowing on the resistance and recovery of temperate semiarid grassland experiencing a three-year drought. Nitrogen addition increased grassland biomass recovery but decreased structural recovery after drought, whereas annual mowing increased grassland biomass recovery and structural recovery but reduced structural resistance to drought. The treatment effects on community biomass/structural resistance and recovery were largely modulated by the stability of the dominant species and asynchronous dynamics among species, and the community biomass resistance and recovery were also greatly driven by the stability of grasses. Community biomass resistance/recovery in response to drought was positively associated with its corresponding structural stability. Our study provides important experimental evidence that both nitrogen addition and mowing could substantially change grassland stability in both functional and structural aspects. Our findings emphasize the need to study changes across levels of ecological organization for a more complete understanding of ecosystem responses to disturbances under widespread environmental changes.

Using leaf traits to explain species co-existence and its consequences for primary productivity across a forest-steppe ecotone.

Trait-based approaches have been widely applied to uncover the mechanisms determining community assembly and biodiversity-ecosystem functioning relationships. However, they have rarely been used in forest-steppe ecotones. These ecosystems are extremely sensitive to disturbances due to their relatively complex ecosystem structures, functionings and processes. In this study, we selected seven sites along a transect from closed canopy forests (CF) to forest-steppe ecotones (FSE) and meadow steppes (MS) in northeast China. Six leaf functional traits (i.e. leaf nitrogen and phosphorus contents, leaf length and thickness, single leaf area and leaf mass per unit area, LMA) as well as the community composition and aboveground biomass at each site were measured. Both functional trait diversity indices (richness, evenness and divergence) and community-weighted mean trait values (CWMs) were calculated to quantify community trait distributions. We found that dominant species in the FSE communities showed acquisitive strategies with highest leaf nitrogen (Mean ± SE: 19.6 ± 0.5 mg g-1) and single leaf area (19.2 ± 1.3 cm2), but the lowest LMA (59.6 ± 1.3 g cm-2) values compared to adjacent CF and MS communities. The ecotone communities also exhibited the largest functional trait richness (TOP), evenness (TED) and divergence (FDis) values (0.46, 0.92 and 0.67, respectively). Overall, niche differentiation emerges as the main mechanism influencing the coexistence of plant species in ecotone ecosystems. In addition, CWMs of leaf traits were the most important predictors for estimating variations in aboveground productivity across the transect, suggesting a major influence of dominant species. Our findings suggest that vegetation management practices in forest-steppe ecotones should increasingly focus on community functional trait diversity, and support the establishment and regeneration of plant species with rapid resource acquisition strategies.

[Changes of persistent soil seed bank along a precipitation gradient in forest-steppe ecotone]. / æ£®æž—è‰åŽŸè¿‡æ¸¡å¸¦æŒä¹ åœŸå£¤ç§å­åº“æ²¿é™æ°´æ¢¯åº¦çš„æ ¼å±€.

This study aimed to examine the responses of persistent soil seed bank to future precipitation reduction of global climate change in the forest-steppe ecotone of Hulunbuir. Samples of soil seed bank were collected from 0-10 cm soil layer along a precipitation gradient. We examined the density, species composition, diversity of seed bank and their relationship with vegetation. Structural equation model was used to explore the direct impact of annual precipitation on soil seed bank and the indirect impact through vegetation, soil nitrogen, soil phosphorus, and soil pH. The results showed that seed bank density and species richness were negatively correlated with annual precipitation. The species diversity of soil seed banks in grasslands was higher than that in forests. The similarity between soil seed bank and vegetation was generally low. The results of structural equation model showed that the effects of annual precipitation on seed bank density and species richness were negative, with the standard path coefficients of -0.051 and -0.122, respectively. The direct effect of annual precipitation on seed bank density and species richness were positive. Precipitation had indirect and positive effect on seed bank density and species richness through soil nitrogen, a significantly indirect negative effect on seed bank species richness through soil pH and soil available phosphorus, and a significantly indirect negative effect on seed bank density through soil pH. The reduction of precipitation under furture climate change might alter the hedging strategies of plants. The persistent soil seed bank in the forest-steppeecotone had a potential buffering effect against future precipitation reduction.

[Changes of non-structural carbohydrates and nitrogen contents of needles and twigs in Pinus sylvestris var. mongolica plantations along an aridity gradient]. / 沿干旱梯度樟子松人工林针叶和枝条非结构性碳水化合物及氮含量的变化.

With six Pinus sylvestris var. mongolica plantations (Huinan, Xifeng, Fujia, Zhanggutai, Naiman and Wulanaodu) along an aridity gradient in the Horqin sandy land, we examined the changes in non-structural carbohydrates (NSCs) and nitrogen (N) contents of current and one-year-old needles and twigs, to explore the carbon supply and demand status as well as the nutrient accumulation strategies of P. sylvestris var. mongolica under drought. The results showed that the contents of NSCs and soluble sugars in needles and twigs of P. sylvestris var. mongolica plantations significantly decreased with increasing aridity. From the most humid site (Huinan) to the most aridity site (Wulanaodu), the soluble sugar contents in current and one-year old needles of P. sylvestris var. mongolica decreased from 12.8% and 12.5% to 9.0% and 9.5%, respectively. The soluble sugar contents in current-year old twigs decreased from 15.6% to 9.2%. With increasing aridity, the starch contents in needles and twigs remained relatively stable, soluble sugars/starch ratio in current and one-year old needles decreased, the N contents in current and one-year old twigs significantly increased. The P. sylvestris var. mongolica plantations in the Horqin sandy land consumed soluble sugar storage under drought, resulting in a risk of mortality from 'carbon starvation'. P. sylvestris var. mongolica tended to maintain stable starch storage and accumulate N in twigs to cope with long-term drought stress.

[Effects of nutrient and water addition on soil inorganic phosphorus fractions in an old-field grassland]. / å »åˆ†å’Œæ°´æ·»åŠ å¯¹å¼ƒè€•è‰åœ°åœŸå£¤æ— æœºç£·ç»„åˆ†çš„å½±å“.

Reasonable nutrient and water management is effective ways to improve productivity and biodiversity of degraded grasslands. However, little is known about the effects of nutrient and water addition on soil inorganic phosphorus (P) fractions in old-field grasslands. Based on a field experiment with nutrient addition (N: 10 g·m-2·a-1, P: 10 g·m-2·a -1) and water addition (180 mm water irrigated during plant growing season) in Duolun County, Inner Mongolia in 2005, we examined the changes of inorganic P fractions and Olsen-P contents in the topsoil (0-10 cm). Results showed that 11-year P addition significantly increased total inorganic P (TIP) content, and that exogenous P was mostly transformed into calcium phosphate (Ca-P: 62.6%-69.2%), and then into aluminium phosphate (Al-P: 19.9%-25.1%), ferric phosphate (Fe-P) and occluded P (O-P). Phosphorus incorporated with nitrogen (N) addition significantly increased Fe-P and Al-P contents by declining soil pH and activating Fe3+ and Al3+ in soil. Water addition alone significantly increased Fe-P, Al-P, and decalcium phosphate (Ca10-P) fractions, and the contents of Fe-P, Al-P, octacalcium phosphate (Ca8-P), and Ca10-P were greater in P incorporated with water treatment than in P addition alone. There was no difference of each inorganic P fraction between P incorporated with N and water treatment and P incorporated with N treatment. Phosphorus and P incorporated with N additions significantly increased soil Olsen-P content, while water addition significantly decreased soil Olsen-P content under P addition alone and P incorporated with N treatment. In the calcareous soils, calcium superphosphate addition could enhance soil inorganic P pool through increasing Ca-P fraction.

A new approach to the treatment of nontuberculous mycobacterium skin infections caused by iatrogenic manipulation: Photodynamic therapy combined with antibiotics: A pilot study.

BACKGROUND: Recently, the number of nontuberculous mycobacterium (NTM) infections caused by iatrogenic procedures, especially rapid NTM skin infections, has been increasing. Due to the nonspecific clinical manifestations and nonstandard treatment guidelines, these infections are often misdiagnosed and challenging to treat. METHODS: In this study, eight patients had NTM skin infections caused by iatrogenic procedures, and were diagnosed by bacterial culture and flight mass spectrometry tests. They were treated with 5-aminolevulinic acid-photodynamic therapy (ALA-PDT) combined with antibiotic therapy. RESULTS: All eight patients enrolled in the study were cured with 100% efficacy after receiving combination therapy with ALA-PDT and antibiotics for 3-6 months. All patients experienced redness and pain during treatment but no other discomfort and were satisfified with the results of their treatments. CONCLUSION: Local ALA-PDT combined with antibiotics is a safe and effective method of treating NTM skin infections.

Nitrogen enrichment buffers phosphorus limitation by mobilizing mineral-bound soil phosphorus in grasslands.

Phosphorus (P) limitation is expected to increase due to nitrogen (N)-induced terrestrial eutrophication, although most soils contain large P pools immobilized in minerals (Pi ) and organic matter (Po ). Here we assessed whether transformations of these P pools could increase plant available pools alleviating P limitation under enhanced N availability. The mechanisms underlying these possible transformations were explored by combining results from a 10-year field N addition experiment and a 3700-km transect covering wide ranges in soil pH, soil N, aridity, leaching, and weathering that could affect soil P status in grasslands. Nitrogen addition promoted the dissolution of immobile Pi (mainly Ca-bound recalcitrant P) to more available forms of Pi (including Al- and Fe-bound P fractions and Olsen P) by decreasing soil pH from 7.6 to 4.7, but did not affect Po . Soil total P declined by 10% from 385 ± 6.8 to 346 ± 9.5 mg kg-1 , whereas available P increased by 546% from 3.5 ± 0.3 to 22.6 ± 2.4 mg kg-1 after the 10-year N addition, associated with an increase in Pi mobilization, plant uptake, and leaching. Similar to the N addition experiment, the drop in soil pH from 7.5 to 5.6 and increase in soil N concentration along the grassland transect were associated with an increased ratio between relatively mobile Pi and immobile Pi . Our results provide a new mechanistic understanding of the important role of soil Pi mobilization in maintaining plant P supply and accelerating biogeochemical P cycles under anthropogenic N enrichment. This mobilization process temporarily buffers ecosystem P limitation or even causes P eutrophication, but will extensively deplete soil P pools in the long run.

Effects of nitrogen addition on plant-soil micronutrients vary with nitrogen form and mowing management in a meadow steppe.

Nitrogen (N) addition and mowing can significantly influence micronutrient cycling in grassland ecosystems. It remains largely unknown about how different forms of added N affect micronutrient status in plant-soil systems. We examined the effects of different N compounds of (NH4)2SO4, NH4NO3, and urea with and without mowing on micronutrient Fe, Mn, Cu, and Zn in soil-plant systems in a meadow steppe. The results showed that (NH4)2SO4 addition had a stronger negative effect on soil pH compared with NH4NO3 and urea, resulting in higher increases in soil available Fe and Mn herein. Nitrogen addition decreased plant community-level biomass weighted (hereafter referred to as community-level) Fe concentration but increased Mn concentration, with a greater effect under (NH4)2SO4 addition. Community-level Cu concentration increased with (NH4)2SO4 and NH4NO3 addition only under mowing treatment. Mowing synergistically interacted with urea addition to increase community-level Mn and Zn concentrations even with decreased soil organic matter, possibly because of compensatory plant growth and thus higher plant nutrient uptake intensity under mowing treatment. Overall, responses of plant-soil micronutrients to N addition varied with mowing and different N compounds, which were mainly regulated by soil physicochemical properties and plant growth. Different magnitude of micronutrient responses in plants and soils shed light on the necessity to consider the role of various N compounds in biogeochemical models when projecting the effects of N enrichment on grassland ecosystems.

Natural abundance of 13 C and 15 N provides evidence for plant-soil carbon and nitrogen dynamics in a N-fertilized meadow.

Natural abundance of carbon (C) and nitrogen (N) stable isotope ratios (δ13 C and δ15 N) has been used to indicate ecosystem C and N status and cycling; however, use of this approach to infer plant and microbial N preference under projected ecosystem N enrichment is limited. Here, we investigated natural abundance δ13 C and δ15 N of five dominant plant species, and soil δ15 N of microbial biomass and available N forms under N addition in a meadow steppe. Additional N, applied as urea, led to decreases in δ15 N of soil NO3- (δ15 Nnitrate , from 3.0 to 0.4‰) and increases in δ15 N of soil NH4+ (δ15 Nammonium , from -1.3 to 11‰) and dissolved organic N (δ15 NDON , from 8.5 to 15‰) that reflected increased net nitrification rates, a possible increase in NH3 volatilization, and greater availability of the three N forms. An overall increase in δ15 N of soil total N (δ15 NTN ) from 7.1 to 7.9‰ indicated accelerated and greater openness of soil N cycling that was also partially revealed by enhanced net N mineralization rates. Plant δ15 N, which ranged from -1.8 to 2.1‰, generally decreased with N addition, indicating a greater reliance on soil NO3- under N-enrichment conditions. Nitrogen addition decreased δ15 N of microbial biomass N (from 14 to 2.8‰), possibly because of a shift in preferential N form (DON to NO3- ), that indicated a convergence of plant and microbial preferential N forms and an increase in plant-microbial N competition. Microbes were thus more flexible than plants in the use of different forms of N. Addition of N decreased plant litter δ13 C, whereas plant species δ13 C remained unaffected, likely because of a shift in the abundance of dominant species with a greater proportion of biomass coming from δ13 C-depleted species. Enrichment factor (the difference in plant δ15 N relative to δ15 NTN ) of four nonlegume species was negatively related to soil inorganic N availability, net nitrification rate, and net N mineralization rate, and was proven to be a good indicator of ecosystem N status. Our study highlights the importance of natural abundance of 15 N as an indicator of plant-microbial N competition and ecosystem N cycling in meadow steppe grasslands under projected ecosystem N enrichment.

Intensity and frequency of nitrogen addition alter soil chemical properties depending on mowing management in a temperate steppe.

Anthropogenic nitrogen (N) enrichment can significantly alter soil chemical properties in various ecosystems. Previous manipulative N experiments mainly focused on the intensity of N addition on soil properties by changing N input rates. It remains unclear, however, whether frequency of N addition can affect soil chemical properties. We examined the effects of frequency (2 versus 12 applications yr-1) and rate (ranging from 0 to 50 g N m-2 yr-1) of N addition on soil chemical properties of pH, base cations, soil pH buffering capacity (pHBC), and soil available micronutrients in a temperate steppe with and without mowing. Mowing significantly increased the effective cation exchange capacity (ECEC), soil exchangeable Ca and Na, available Fe, and soil pHBC when N was applied at low frequency. Low frequency of N addition significantly decreased soil pH and exchangeable Na but increased soil exchangeable Mg without mowing; however, it increased soil exchangeable Na and available Zn with mowing, while available Fe and Mn increased both with and without mowing. Higher rates of N addition (≥20 g N m-2 yr-1) decreased soil pH, ECEC and exchangeable Ca but increased soil available Fe, Mn and Cu regardless of the mowing treatment and frequency of N addition. Changes in soil organic matter, pHBC and ECEC were the main reasons affecting soil pH across mowing and N application treatments. Our results indicate that frequency of N addition played an essential role in altering soil chemical properties. Simulating N deposition via large and infrequent N additions can underestimate (exchangeable Mg and available Fe and Mn) or overestimate (soil pH and exchangeable Na) changes in soil properties. Our results further suggest that the effects of frequency of N addition on soil chemical attributes in semi-arid grassland ecosystems can be regulated by appropriate mowing management.

Effects of nitrogen and water addition on trace element stoichiometry in five grassland species.

A 9-year manipulative experiment with nitrogen (N) and water addition, simulating increasing N deposition and changing precipitation regime, was conducted to investigate the bioavailability of trace elements, iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in soil, and their uptake by plants under the two environmental change factors in a semi-arid grassland of Inner Mongolia. We measured concentrations of trace elements in soil and in foliage of five common herbaceous species including 3 forbs and 2 grasses. In addition, bioaccumulation factors (BAF, the ratio of the chemical concentration in the organism and the chemical concentration in the growth substrate) and foliar Fe:Mn ratio in each plant was calculated. Our results showed that soil available Fe, Mn and Cu concentrations increased under N addition and were negatively correlated with both soil pH and cation exchange capacity. Water addition partly counteracted the positive effects of N addition on available trace element concentrations in the soil. Foliar Mn, Cu and Zn concentrations increased but Fe concentration decreased with N addition, resulting in foliar elemental imbalances among Fe and other selected trace elements. Water addition alleviated the effect of N addition. Forbs are more likely to suffer from Mn toxicity and Fe deficiency than grass species, indicating more sensitivity to changing elemental bioavailability in soil. Our results suggested that soil acidification due to N deposition may accelerate trace element cycling and lead to elemental imbalance in soil-plant systems of semi-arid grasslands and these impacts of N deposition on semi-arid grasslands were affected by water addition. These findings indicate an important role for soil trace elements in maintaining ecosystem functions associated with atmospheric N deposition and changing precipitation regimes in the future.

Glucose deprivation induces chemoresistance in colorectal cancer cells by increasing ATF4 expression.

AIM: To investigate the role of activating transcription factor 4 (ATF4) in glucose deprivation (GD) induced colorectal cancer (CRC) drug resistance and the mechanism involved. METHODS: Chemosensitivity and apoptosis were measured under the GD condition. Inhibition of ATF4 using short hairpin RNA in CRC cells under the GD condition and in ATF4-overexpressing CRC cells was performed to identify the role of ATF4 in the GD induced chemoresistance. Quantitative real-time RT-PCR and Western blot were used to detect the mRNA and protein expression of drug resistance gene 1 (MDR1), respectively. RESULTS: GD protected CRC cells from drug-induced apoptosis (oxaliplatin and 5-fluorouracil) and induced the expression of ATF4, a key gene of the unfolded protein response. Depletion of ATF4 in CRC cells under the GD condition can induce apoptosis and drug re-sensitization. Similarly, inhibition of ATF4 in the ATF4-overexpressing CRC cells reintroduced therapeutic sensitivity and apoptosis. In addition, increased MDR1 expression was observed in GD-treated CRC cells. CONCLUSION: These data indicate that GD promotes chemoresistance in CRC cells through up-regulating ATF4 expression.

miR-139-5p sensitizes colorectal cancer cells to 5-fluorouracil by targeting NOTCH-1.

Multidrug resistance (MDR), a phenomenon that often occurs with drug treatment and is characterized by relapse or attenuation of drug efficacy, is almost unavoidable in colorectal cancer (CRC) patients receiving 5-fluorouracil (5-FU)-based chemotherapy. MicroRNAs (miRNAs) are small noncoding RNAs that post-transcriptionally regulate gene expression. Our previous study has identified miR-139-5p as a potential tumor suppressor in CRC, but its role in chemoresistance of CRC has not been elucidated. In this study, we demonstrated that miR-139-5p was down-regulated either in CRC tumors receiving chemotherapy or in 5-FU-resistant CRC cell lines (HCT-8/5-FU and HCT-116/5-FU). Ectopic expression of miR-139-5p sensitized CRC cells to 5-FU by increasing 5-FU-induced apoptosis. In addition, miR-139-5p inhibited the expression of the miR-139-5p target gene NOTCH-1 and its downstream molecules MRP-1 and BCL-2, two key MDR-associated genes. Furthermore, silencing NOTCH-1 expression promoted the chemotherapeutic effects of 5-FU, and up-regulation of NOTCH-1 abrogated miR-139-5p-mediated sensitization to 5-FU in LoVo and HCT-116 cells. Taken together, our data indicate a new role of miR-139-5p/NOTCH-1 pathway in the drug resistance of CRC cells to 5-FU, which may be a promising therapeutic target for the anti-MDR treatment of CRC.

LncRNA-UCA1 enhances cell proliferation and 5-fluorouracil resistance in colorectal cancer by inhibiting miR-204-5p.

Recent preliminary studies reported the in vitro tumor-promoting effects of long non-coding RNA urothelial carcinoma associated 1 (UCA1) in colorectal cancer (CRC). However, the in vivo functions and molecular mechanism of UCA1 in CRC remain unclear. Therefore, we investigated the detailed role and mechanism of UCA1 in CRC. We found that UCA1 was up-regulated in CRCs and negatively correlated with survival time in two CRC cohorts. Functional assays revealed the in vitro and in vivo growth-promoting function of UCA1 and revealed that UCA1 can decrease the sensitivity of CRC cells to 5-FU by attenuating apoptosis. Further mechanistic studies revealed that UCA1 could sponge endogenous miR-204-5p and inhibit its activity. We also identified CREB1 as a new target of miR-204-5p. The protein levels of CREB1 were significantly up-regulated in CRCs, negatively associated with survival time and positively correlated with the UCA1 expression. The present work provides the first evidence of a UCA1-miR-204-5p-CREB1/BCL2/RAB22A regulatory network in CRC and reveals that UCA1 and CREB1 are potential new oncogenes and prognostic factors for CRC.

Systematic analysis of key miRNAs and related signaling pathways in colorectal tumorigenesis.

The development of colorectal cancers (CRC) is accompanied with the acquisition and maintenance of specific genomic alterations. These alterations can emerge in premalignant adenomas and faithfully maintained in highly advanced tumors. miRNAs are a class of small non-coding RNAs that are frequently deregulated in human cancers and negatively regulate a wide variety of protein coding genes. To identify the sequential alterations of miRNAs and its regulatory networks during CRC development and progression, we detected the miRNA expression profiles of tissue samples from normal colon, colorectal adenoma and CRC using miRNA microarray. qRT-PCR assay was used to validate and select the miRNAs with differential expression among the three groups, and the computer-aided algorithms of TargetScan, miRanda, miRwalk, RNAhybrid and PicTar were used to search for the possible targets of the selected 8 miRNAs (miR-18a, miR-18b, miR-31, miR-142-5p, miR-145, miR-212, miR-451, and miR-638) with continuous alterated expression. These potential target genes were enriched in several key signal transduction pathways (KEGG pathway analysis), which have been proved to be closely related to colorectal tumorigenesis. To confirm the reliability of the analyses, we identified that the metastasis-related gene ZO-1 is a certain target of miR-212 in CRC and keeps declining during CRC progression. By following these analyses, we might gain an in-depth understanding of the molecular regulatory networks of colorectal tumorigenesis and provide new potential targets for the diagnostic and therapeutic interventions of this disease.