Exosome biogenesis: machinery, regulation, and therapeutic implications in cancer.

Exosomes are well-known key mediators of intercellular communication and contribute to various physiological and pathological processes. Their biogenesis involves four key steps, including cargo sorting, MVB formation and maturation, transport of MVBs, and MVB fusion with the plasma membrane. Each process is modulated through the competition or coordination of multiple mechanisms, whereby diverse repertoires of molecular cargos are sorted into distinct subpopulations of exosomes, resulting in the high heterogeneity of exosomes. Intriguingly, cancer cells exploit various strategies, such as aberrant gene expression, posttranslational modifications, and altered signaling pathways, to regulate the biogenesis, composition, and eventually functions of exosomes to promote cancer progression. Therefore, exosome biogenesis-targeted therapy is being actively explored. In this review, we systematically summarize recent progress in understanding the machinery of exosome biogenesis and how it is regulated in the context of cancer. In particular, we highlight pharmacological targeting of exosome biogenesis as a promising cancer therapeutic strategy.

Angiopoietin-2 induces angiogenesis via exosomes in human hepatocellular carcinoma.

BACKGROUND: Hepatocellular carcinoma (HCC) is the most common primary liver cancer and is a highly vascularized solid tumor. Angiopoietin-2 (ANGPT2) has been described as an attractive target for antiangiogenic therapy. Exosomes are small extracellular vesicles secreted by most cell types and contribute to cell-to-cell communication by delivering functional cargo to recipient cells. The expression of ANGPT2 in tumor-derived exosomes remains unknown. METHODS: We detected the ANGPT2 expression in HCC-derived exosomes by immunoblotting, enzyme-linked immunosorbent assay and immunogold labeling, then observed exosomal ANGPT2 internalization and recycling by confocal laser scanning microscopy, co-immunoprecipitation and immunoblotting. We used two HCC cell lines (Hep3B and MHCC97H) to overexpress ANGPT2 by lentivirus infection or knockdown ANGPT2 by the CRISPR/Cas system, then isolated exosomes to coculture with human umbilical vein endothelial cells (HUVECs) and observed the angiogenesis by Matrigel microtubule formation assay, transwell migration assay, wound healing assay, cell counting kit-8 assay, immunoblotting and in vivo tumorigenesis assay. RESULTS: We found that HCC-derived exosomes carried ANGPT2 and delivered it into HUVECs by exosome endocytosis, this delivery led to a notable increase in angiogenesis by a Tie2-independent pathway. Concomitantly, we observed that HCC cell-secreted exosomal ANGPT2 was recycled by recipient HUVECs and might be reused. In addition, the CRISPR-Cas systems to knock down ANGPT2 significantly inhibited the angiogenesis induced by HCC cell-secreted exosomal ANGPT2, and obviously suppressed the epithelial-mesenchymal transition activation in HCC. CONCLUSIONS: Taken together, these results reveal a novel pathway of tumor angiogenesis induced by HCC cell-secreted exosomal ANGPT2 that is different from the classic ANGPT2/Tie2 pathway. This way may be a potential therapeutic target for antiangiogenic therapy. Video Abstract.

Vps4A functions as a tumor suppressor by regulating the secretion and uptake of exosomal microRNAs in human hepatoma cells.

UNLABELLED: The deregulation of microRNAs (miRNAs) plays an important role in human hepatocarcinogenesis. In this study, we highlight exosomes as mediators involved in modulating miRNA profiles in hepatocellular carcinoma (HCC) cells. First, we examined the different miRNA expression profiles in HCC cells and HCC cell-derived exosomes. Next, coculture experiments indicated that HCC cell-derived exosomes promoted the cell growth, migration, and invasion of HCC cells and had the ability to shuttle miRNAs to recipient cells. Further, our data showed that Vps4A, a key regulator of exosome biogenesis, was frequently down-regulated in HCC tissues. The reduction of Vps4A in HCC tissues was associated with tumor progression and metastasis. In vitro studies revealed that Vps4A repressed the growth, colony formation, migration, and invasion of HCC cells. We further investigated the role and involvement of Vps4A in suppressing the bioactivity of exosomes and characterized its ability to weaken the cell response to exosomes. By small RNA sequencing, we demonstrated that Vps4A facilitated the secretion of oncogenic miRNAs in exosomes as well as accumulation and uptake of tumor suppressor miRNAs in cells. A subset of Vps4A-associated miRNAs was identified. Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that the phosphatidylinositol-3-kinase/Akt signaling pathway was the most likely candidate pathway for modulation by these miRNAs. Indeed, we proved that the phosphatidylinositol-3-kinase/Akt pathway was inactivated by Vps4A overexpression. CONCLUSION: Exosome-mediated miRNA transfer is an important mechanism of self-modulation of the miRNA expression profiles in HCC cells, and Vps4A may function as a tumor suppressor, which utilizes exosomes as mediators to regulate the secretion and uptake of miRNAs in hepatoma cells; these observations provide new insights into the development of HCC.

[Research progress on the dual-mulching of ridge and furrow technology in dry farming regions of northern China: A review.] / åŒ—æ–¹æ—±ä½œåŒºæ²Ÿåž„äºŒå ƒè¦†ç›–æŠ€æœ¯ç ”ç©¶è¿›å±•.

The precipitation exiguity and water deficiency are the major factors limiting crop growth in dry farming regions of northern China. Dual-mulching of ridges and furrows, which have been widely concerned both domestically and internationally, could increase the utilization efficiency of precipitation and crop yield. In this paper, we reviewed the concept and model of dual-mulching of ridges and furrows, its supporting farm machinery and implements as well as its ecological effects on soil and crops. Based on the current research progress of cultivation techniques using harvested rainfall in ridge and furrow, priority of future research aspects of the dual-mulching of ridges and furrows were suggested as follows: 1) to establish the suitable ridge-furrow ratios for different crops in different types of dry farming regions of northern China; 2) to pay more attention to the study of coupling effects of soil moisture with temperature, fertility and other factors; 3) to explore better environment-friendly mulching materials; 4) to enhance the research on technical evaluation and popularization, and the design of supporting farm machinery and implements.

[Effects of ridge and furrow rain harvesting with supplemental irrigation on winter wheat photosynthetic characteristics, yield and water use efficiency in Guanzhong irrigation district].

A field experiment was conducted to determine the regulation of crop photosynthesis and output and water saving effect under ridge and furrow rain harvesting with supplemental irrigation in Guanzhong irrigation district. The experiment was set with 5 treatments with irrigation at returning green stage, and the widths of both ridge and furrow being 60 cm. T1, T2 and T3 were in the ridge and furrow rain harvesting planting pattern, with the irrigation volumes being 0, 375 and 750 m3 · hm(-2) respectively, T4 was flat planting with irrigation (border irrigation) of 750 m3 · hm(-2) and CK was flat planting without irrigation. Effects on winter wheat photosynthetic organs, photosynthetic rate, yield and water use efficiency, etc. were tested. The results showed that compared with T4, T1, T2 and T3 treatments increased the grain yield by 2.8%, 9.6% and 18.9%, improved the harvest index by 2.0% to 8.5%, advanced the flag leaf chlorophyll content by 41.9% to 64.4% significantly, and improved the 0-40 cm layer soil moisture content by 0.1%-4.6% during the whole growth period. Photosynthetic rates at the flowering and filling stages also increased by 22.3% to 54.2% and -4.3% to 67.2%, respectively. Total water use efficiencies (WUEy) were 17.9%, 10.4% and 15.4% higher than that of T4, and 69.3%, 58.6% and 65.7% higher than that of CK (P < 0.05), respectively, and enhanced precipitation utilization efficiency ( PUE ) by 94.3%-124.5% than CK. Leaf areas of T2 and T3 treatments at each growth stage were significantly higher than that of T4 and CK, irrigation water use efficiencies (IUE) were 119.1% and 18.8% higher than that of T4, respectively. Therefore, it was concluded that ridge and furrow rain harvesting cultivation could maintain higher grain yield than border irrigation without irrigation or with irrigation reduction by 50%. The utilization efficiency of irrigation water under the condition of irrigation reduction by 50% was improved significantly, and the ridge and furrow rain harvesting could significantly improve whole cropland water use efficiency in the year of less rainfall.

[Effects of straw mulching on soil moisture and watermelon yield in dryland].

To explore the effects of straw mulching on soil moisture and yield of watermelon, corn straw was used as mulching materials, and three straw mulch treatments were performed, i. e., whole mulch (WM), rows mulch (SM) and root domain mulch (RM), and non-mulching as control. The results indicated that WM and RM treatments increased significantly soil water storage in 0-120 cm of soil layer under root domain and rows compared with the control during watermelon growth period, and soil water storage of RM was higher than that of SM after growing tendril. Effects of all straw mulch treatments on soil moisture were most obvious from watermelon post-growing tendril to pre-swelling and maturity. With the growth and development of watermelon, the three straw mulch treatments improved soil moisture around root domain, resulting in increased watermelon yields. Compared with the CK, the WM, SM and RM treatments significantly improved the yield and the water use efficiency of watermelon by 24.8%, 11.5% and 15.1%, and 42.7%, 24.3% and 29.4%. The WM with 13500 kg x hm(-2) straw was recommended for watermelon production in arid areas due to its favorable effect on soil storage moisture, yield and water use efficiency.

[Effects of strip planting and fallow rotation on the soil and water loss and water use efficiency of slope farmland].

In order to enhance the soil water-retaining capacity of slope farmland and reduce its soil and water loss, a field study was conducted in 2007-2010 to examine the effects of strip planting and fallow rotation on the soil water regime, soil and water loss characteristics, and water use efficiency of a 10 degrees-15 degrees slope farmland in the arid area of southern Ningxia, Northwest China. Compared with the traditional no-strip planting, strip planting and fallow rotation increased the soil water content in 0-200 cm layer significantly, with an increment of 4.9% -7.0%. Strip planting and fallow rotation pattern could also effectively conserve the soil water in rain season, and obviously improve the soil water regime at crops early growth stages. As compared to no-strip planting, strip planting and fallow rotation increased the soil water content in 0-200 cm layer by 5.4%-8.5%, decreased the surface runoff by 0.7-3.2 m3 x hm(-2), sediment runoff by 0.2-1.9 t x hm(-2), and soil total N loss by 42.1% -73.3%, while improved the crop water use efficiency by 6.1% -24.9% and the precipitation use efficiency by 6.3% -15.3%.

[Effects of straw mulching on the soil aggregates in dryland wheat field under no-tillage].

A field experiment was conducted to study the effects of full period and growth period straw mulching with an amount of 3000, 6000, and 9000 kg x hm(-2) on the soil aggregates in a no-tillage dryland wheat field in Weibei Loess Pleateau of Shaanxi Province, taking no full period straw mulching as the control. In the 0-40 cm soil layer, the content of > 5 mm aggregates increased with depth, while that of <5 mm aggregates was in adverse. Under straw mulching, the total contents of > 0.25 mm mechanical stable aggregates (DR0.25) and of > 0.25 mm water stable aggregates (WR0.25) were significantly higher than the control, with an increase of 13.0%-26.4% and 18.6%-45.6%, respectively and the largest increment in the treatment 6000 kg x hm(-2) of straw mulching. Straw mulching increased the soil organic matter content, and the latter had a significant positive correlation with the WR0.25 content. All the straw mulching treatments decreased the soil unstable aggregate index (E(LT)) which was the lowest in treatment 6000 kg x hm(-2) of straw mulching. This study showed that straw mulching could increase the >0.25 mm aggregates and organic matter contents in 0-40 cm soil layer and improve the soil structural stability, and mulching with an amount of 6000 kg x hm(-2) had the best effect, being a reasonable straw mulching mode to be applied in the agricultural production in Weibei Loess Plateau.

[Effects of rotational tillage during summer fallow on wheat field soil water regime and grain yield].

In 2007-2010, a field experiment was conducted to study the effects of different rotational tillage practices during summer follow on the soil water regime and grain yield in a winter wheat field in Southern Ningxia arid area. Three treatments were installed, i.e., T1 (no-tillage in first year, subsoiling in second year, and no-tillage in third year), T2 (subsoiling in first year, notillage in second year, and subsoiling in third year), and CT (conventional tillage in the 3 years). Through the three years of the tillage practices, the soil water storage efficiency in treatments T1 and T2 was increased averagely by 15.2% and 26.5%, respectively, as compared to CT. In treatments T1 and T2, the potential rainfall use rate was higher, being 37.8% and 38.5%, respectively, and the rainfall use efficiency was increased averagely by 9.9% and 10.7%, respectively, as compared to CT. Rotational tillage during summer fallow could decrease the soil ineffective evaporation significantly, and save the soil water effectively in wheat growth season. At early growth stage, the water storage in 0-200 cm soil layer in treatments T1 and T2 was increased averagely by 6.8% and 9. 4%, as compared to CT; at jointing, heading, and filling stages, the water storage in 0-200 cm soil layer in treatments T1 and T2 had a significant increase, giving greater contribution to the wheat yield than the control. Different rotational tillage practices increased the water consumption by wheat, but in the meantime, increased the grain yield and water use efficiency. In treatments T1 and T2, the water consumption by wheat through the three years was increased averagely by 5.2% and 6.1%, whereas the grain yield and the water use efficiency were increased averagely by 9.9% and 10.6%, and by 4.5% and 4.3%, respectively, as compared to CT. Correlation analysis showed that in Southern Ningxia arid area, the soil water storage at sowing, jointing, heading, and filling stages, especially at heading stage, could have significant effects on the winter wheat grain yield.