Stimulation of site-specific phosphorylation of acetyl coenzyme A carboxylase by insulin and epinephrine

32P-labeled acetyl-CoA carboxylase was isolated from 32P-labeled rat epididymal fat pads by avidin-Sepharose affinity chromatography after exposure to epinephrine and insulin. Epinephrine led to an inactivation of the isolated enzyme by a reduction of Vmax, while the insulin stimulation observed in crude extracts did not survive enzyme purification. Both insulin and epinephrine caused only small increases in total 32P content of the enzyme. However, mapping of tryptic 32P-phosphopeptides by high performance liquid chromatography revealed that epinephrine and insulin stimulated the phosphorylation of 32P-peptides specific for each hormone. The major 32P-peptide phosphorylated by epinephrine co-migrated with the major 32P-peptide phosphorylated in vitro by the cAMP-dependent protein kinase, while the 32P-peptide phosphorylated in response to insulin co-migrated with that phosphorylated by casein kinase-I and casein kinase-II. The effects of epinephrine on carboxylase activity and phosphorylation can thus be accounted for by the expected epinephrine-induced activation of the cAMP-dependent protein kinase. While the increase in site-specific phosphorylation caused by insulin cannot be directly linked to insulin-induced activation in crude extracts, these data suggest that casein kinase-I and/or casein kinase-II may mediate the insulin-stimulated phosphorylation of acetyl-CoA carboxylase.     

Regulation of channel gating by AMP-activated protein kinase modulates cystic fibrosis transmembrane conductance regulator activity in lung submucosal cells

Cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel activity is important for fluid and electrolyte transport in many epithelia including the lung, the site of most cystic fibrosis-associated morbidity. CFTR is unique among ion channels in requiring ATP hydrolysis for its gating, suggesting that its activity is coupled to cellular metabolic status. The metabolic sensor AMP-activated kinase (AMPK) binds to and phosphorylates CFTR, co-localizes with it in various tissues, and inhibits CFTR currents in Xenopus oocytes (Hallows, K. R., Raghuram, V., Kemp, B. E., Witters, L. A. & Foskett, J. K. (2000) J. Clin. Invest. 105, 1711-1721). Here we demonstrate that this AMPK-CFTR interaction has functional implications in human lung epithelial cells. Pharmacologic activation of AMPK inhibited forskolin-stimulated CFTR short circuit currents in polarized Calu-3 cell monolayers. In whole-cell patch clamp experiments, the activation of endogenous AMPK either pharmacologically or by the overexpression of an AMPK-activating non-catalytic subunit mutant (AMPK-gamma1-R70Q) dramatically inhibited forskolin-stimulated CFTR conductance in Calu-3 and CFTR-expressing Chinese hamster ovary cells. Plasma membrane expression of CFTR, assessed by surface biotinylation, was not affected by AMPK activation. In contrast, the single channel open probability of CFTR was strongly reduced in cell-attached patch clamp measurements of Calu-3 cells transfected with the AMPK-activating mutant, an effect due primarily to a substantial prolongation of the mean closed time of the channel. As a metabolic sensor in cells, AMPK may be important in tuning CFTR activity to cellular energy charge, thereby linking transepithelial transport and the maintenance of cellular ion gradients to cellular metabolism.     

燕麦EST-SSR标记的开发和利用

为拓展分子标记在燕麦种质资源分析与鉴定中的应用,利用公共数据库中的25376条EST(expressed sequence tags)序列,开展了燕麦EST-SSR功能性标记的开发和利用研究。25376条EST序列经拼接去冗余后获得了11618条序列,从中筛选出含有不同重复基元的SSR且重复次数较多、长度较长的556条EST序列进行引物设计,开发了50对燕麦EST-SSR引物,通过筛选得到40对有效的EST-SSR引物。选取其中4对引物对5个燕麦种质资源进行了PCR扩增及产物测序,结果表明扩增条带多态性是由SSR差异造成的。利用40对ESTSSR引物对15个六倍体燕麦种质资源进行遗传多样性分析,共扩增出89个等位基因,平均每对引物产生2.23个等位基因;UPGMA聚类分析表明,15个六倍体燕麦种质资源在Dice系数为0.93处聚为3支,基本上是按照不同种进行聚类的,在相同种中又根据地理来源分别聚集成支。利用40对EST-SSR引物对31个遗传背景不清的燕麦种质资源进行基因组倍性鉴定,发现这些种质中可能存在有四倍体和二倍体的燕麦新资源。本研究开发的燕麦EST-SSR功能性标记将在燕麦遗传多样性分析、遗传图谱构建及燕麦属内种间基因组鉴定等方面发挥重要作用。     

The Ca2+/calmodulin-dependent protein kinase kinases are AMP-activated protein kinase kinases

The AMP-activated protein kinase (AMPK) is an important regulator of cellular metabolism in response to metabolic stress and to other regulatory signals. AMPK activity is absolutely dependent upon phosphorylation of AMPKalphaThr-172 in its activation loop by one or more AMPK kinases (AMPKKs). The tumor suppressor kinase, LKB1, is a major AMPKK present in a variety of tissues and cells, but several lines of evidence point to the existence of other AMPKKs. We have employed three cell lines deficient in LKB1 to study AMPK regulation and phosphorylation, HeLa, A549, and murine embryo fibroblasts derived from LKB(-/-) mice. In HeLa and A549 cells, mannitol, 2-deoxyglucose, and ionomycin, but not 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR), treatment activates AMPK by alphaThr-172 phosphorylation. These responses, as well as the downstream effects of AMPK on the phosphorylation of acetyl-CoA carboxylase, are largely inhibited by the Ca(2+)/ calmodulin-dependent protein kinase kinase (CaMKK) inhibitor, STO-609. AMPKK activity in HeLa cell lysates measured in vitro is totally inhibited by STO-609 with an IC50 comparable with that of the known CaMKK isoforms, CaMKKalpha and CaMKKbeta. Furthermore, 2-deoxyglucose- and ionomycin-stimulated AMPK activity, alphaThr-172 phosphorylation, and acetyl-CoA carboxylase phosphorylation are substantially reduced in HeLa cells transfected with small interfering RNAs specific for CaMKKalpha and CaMKKbeta. Lastly, the activation of AMPK in response to ionomycin and 2-deoxyglucose is not impaired in LKB1(-/-) murine embryo fibroblasts. These data indicate that the CaMKKs function in intact cells as AMPKKs, predicting wider roles for these kinases in regulating AMPK activity in vivo.