Downregulation of p57kip2 promotes cell invasion via LIMK/cofilin pathway in human nasopharyngeal carcinoma cells

The members of Rho family are well known for their regulation of actin cytoskeleton to control cell migration. The Cip/kip members of cyclin‐dependent (CDK) inhibitors have shown to implicate in cell migration and cytoskeletal dynamics. p57^kip2, a CDK inhibitor, is frequently down‐regulated in several malignancy tumors. However, its biological roles in human nasopharyngeal carcinoma (NPC) cells remained to be investigated. Here, we found p57^kip2 has nuclear and cytoplasm distributions and depletion of endogenous p57^kip2 did not change the cell‐cycle progression. Inhibition of cell proliferation by mitomycin C promoted FBS‐mediated cell migration and accompanied with the downregulation of ΔNp63α and p57^kip2, but did not change the level of p27^kip1, another CDK inhibitor. By using siRNA transfection and cell migration/invasion assays, we found that knockdown of p57^kip2, but not ΔNp63α, involved in promotion of NPC cell migration and invasion via decrease of phospho‐cofilin (p‐cofilin). Treatment with Y‐27632, a specific ROCK inhibitor, we found that dysregulation of ROCK/cofilin pathway decreased p‐cofilin expression and induced cell migration. This change of p‐cofilin induced actin remodeling and pronounced increase of membrane protrusions. Further, silence of p57^kip2 not only decreased the interaction between p57^kip2 and LIMK‐1 assayed by immunoprecipitation but also reduced the level of phospho‐LIMK1/2. Therefore, this study indicated that dysregulation of p57^kip2 promoted cell migration and invasion through modulation of LIMK/cofilin signaling and suggested this induction of inappropriate cell motility might contribute to promoting tumor cell for metastasis. J. Cell. Biochem. 112: 3459–3468, 2011. © 2011 Wiley Periodicals, Inc.     

ER-localized adenine nucleotide transporter ER-ANT1: an integrator of energy and stress signaling in rice

Most environmental perturbations have a direct or indirect deleterious impact on photosynthesis, and, in consequence, the overall energy status of the cell. Despite our increased understanding of convergent energy and stress signals, the connections between photosynthesis, energy and stress signals through putative common nodes are still unclear. Here we identified an endoplasmic reticulum (ER)-localized adenine nucleotide transporter1 (ER-ANT1), whose deficiency causes seedling lethality in air but viable under high CO₂, exhibiting the typical photorespiratory phenotype. Metabolic analysis suggested that depletion of ER-ANT1 resulted in circadian rhythm disorders in sucrose synthesis and induced sucrose signaling pathways, indicating that the ER is involved in the regulation of vital energy metabolism in plants. In addition, the defect of ER-ANT1 triggers ER stress and activates the unfolded protein response in plant cells, suggesting ER stress and photorespiration are closely linked. These findings provide an important evidence for a key role of ER-localized ER-ANT1 in convergent energy and stress signals in rice. Our findings support the idea that ATP is a central signal involved in the plant response to a variety of stresses.     

Natural variation in GmGBP1 promoter affects photoperiod control of flowering time and maturity in soybean

The present study screened for polymorphisms in coding and non‐coding regions of the GmGBP1 gene in 278 soybean accessions with variable maturity and growth habit characteristics under natural field conditions in three different latitudes in China. The results showed that the promoter region was highly diversified compared with the coding sequence of GmGBP1. Five polymorphisms and four haplotypes were closely related to soybean flowering time and maturity through association and linkage disequilibrium analyses. Varieties with the polymorphisms SNP_‐796G, SNP_‐770G, SNP_‐307T, InDel_‐242normal, SNP_353A, or haplotypes Hap‐3 and Hap‐4 showed earlier flowering time and maturity in different environments. The shorter growth period might be largely due to higher GmGBP1 expression levels in soybean that were caused by the TCT‐motif with SNP_‐796G in the promoter. In contrast, the lower expression level of GmGBP1 in soybean caused by RNAi interference of GmGBP1 resulted in a longer growth period under different day lengths. Furthermore, the gene interference of GmGBP1 also caused a reduction in photoperiod response sensitivity (PRS) before flowering in soybean. RNA‐seq analysis on GmGBP1 underexpression in soybean showed that 94 and 30 predicted genes were significantly upregulated and downregulated, respectively. Of these, the diurnal photoperiod‐specific expression pattern of three significant flowering time genes GmFT2a, GmFT5a, and GmFULc also showed constantly lower mRNA levels in GmGBP1‐i soybean than in wild type, especially under short day conditions. Together, the results showed that GmGBP1 functioned as a positive regulator upstream of GmFT2a and GmFT5a to activate the expression of GmFULc to promote flowering on short days.     

Effects of high temperature on the chlorophyll a fluorescence of Alhagi sparsifolia at the southern Taklamakan Desert

Climate change is expected to result in an increase in the frequency and magnitude of extreme weather events. Alhagi sparsifolia is an important factor for wind prevention and sand fixation in the forelands of the Taklamakan Desert. The effects of high temperature on desert plants remain widely unknown. In this work, chlorophyll a fluorescence induction kinetics were investigated at different time stresses of 5, 20, 40, and 60 min at temperature gradients of 38–44 °C at 2 °C intervals. A pronounced K-step was found, and the values of the maximum quantum yield for primary photochemistry, the quantum yield of electron transport, the density of reaction centers and the performance index on absorption basis were lowest after 60 min at 44 °C, thus indicating that the oxygen-evolving complex was damaged, the inactivated reaction centers increased, and the activity of the photosystem II (PSII) reaction center in leaves was seriously limited. Therefore, we suggest that under normal temperature (below 42 °C), the PSII of A. sparsifolia would be unaffected. When such temperature is maintained for 40 min, the activity of PSII would be limited, and when retained for 60 min, PSII may be severely damaged.