Dynamic panel estimation and homogeneity testing under cross section dependence*

Summary. This paper deals with cross section dependence, homogeneity restrictions and small sample bias issues in dynamic panel regressions. To address the bias problem we develop a panel approach to median unbiased estimation that takes account of cross section dependence. The estimators given here considerably reduce the effects of bias and gain precision from estimating cross section error correlation. This paper also develops an asymptotic theory for tests of coefficient homogeneity under cross section dependence, and proposes a modified Hausman test to test for the presence of homogeneous unit roots. An orthogonalization procedure, based on iterated method of moments estimation, is developed to remove cross section dependence and permit the use of conventional and meta unit root tests with panel data. Some simulations investigating the finite sample performance of the estimation and test procedures are reported.     

Unit root tests and structural change when the initial observation is drawn from its unconditional distribution

Summary Following Elliott (1999; International Economic Review 40, 767–83.) and Perron and Rodríguez (2003; Journal of Econometrics 115,1–27), we develop unit root tests in the context of structural change models using GLS detrended data ( Elliott, Rothenberg and Stock 1996 ; Econometrica 64, 813–39) when the initial observation is drawn from its unconditional distribution. We derive the limiting distributions of the M‐tests ( Stock, 1999 cointegration, causality and forecasting; Oxford University Press, 137–67; Perron and Ng 1996 ; Review of Economics Studies 63, 435–463), the ADF statistic and a feasible optimal point test from which we derive the power envelope. Asymptotic power functions are calculated and compared with the case where the initial condition is not random. Finite sample size and power simulations under various forms of error processes are performed using different lag selection methods and two different methods to select the break point. Empirical applications are also provided.     

circ_0000619通过调控miR-595/GLS轴对食管鳞状细胞癌细胞增殖及谷氨酰胺代谢的影响

目的:探讨circ_0000619/miR-595/GLS轴对人食管鳞状细胞癌（esophageal squamous cell carcinoma,ESCC）KYSE150细胞增殖、迁移、侵袭和谷氨酰胺代谢的影响及其可能的机制。方法:采用qPCR法检测KYSE150细胞中circ_0000619、miR-595、谷氨酰胺酶（glutaminase,GLS）mRNA等表达水平,Western blot检测KYSE150细胞中GLS蛋白的表达情况,使用细胞计数试剂盒-8（cell counting kit-8,CCK-8）试剂盒、Transwell法分别检测KYSE150细胞增殖、迁移及侵袭能力,使用相应的检测试剂盒检测KYSE150细胞谷氨酰胺消耗、谷氨酸产生及ATP产生水平,利用生物信息学分析技术及双荧光素酶报告基因实验分析并检测circ_0000619、miR-595与GLS mRNA之间的相互作用关系。结果:circ_0000619在ESCC细胞系中呈现高表达,其亲本基因DENND4A mRNA在食管癌组织中呈高表达（P<0.01）;敲减circ_0000619显著抑制KYSE150细胞的增殖、侵袭和迁移能力（P<0.01）,并显著抑制KYSE150细胞的谷氨酰胺消耗、谷氨酸及ATP产生水平（P<0.01）;敲减circ_0000619显著上调miR-595表达（P<0.01）,抑制GLS mRNA（P<0.01）及蛋白的表达;双荧光素酶报告基因实验显示在KYSE150细胞中,circ_0000619与miR-595存在靶向结合、miR-595与GLS存在靶向结合（P<0.01）。circ_0000619敲低显著降低了KYSE150细胞谷氨酰胺代谢和细胞增殖,并且这些作用被miR-595抑制或GLS过表达部分逆转。结论:circ_0000619能通过靶向调控miR-595/GLS轴增强ESCC细胞谷氨酰胺代谢及细胞增殖,并可能成为潜在的ESCC治疗靶点。