The Journal of biological chemistry
-
Glycogen synthase kinase-3beta (GSK-3beta) activity is suppressed when it becomes phosphorylated on serine 9 by protein kinase B (Akt). To determine how GSK-3beta activity opposes Akt function we used various methods to alleviate GSK-3beta suppression in prostate carcinoma cells. In some experiments, LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (a kinase involved in activating Akt) and tumor necrosis factor-alpha (TNF-alpha) were used to activate GSK-3beta. ⋯ When transcription factors activator protein-1 and cyclic AMP-response element (CRE)-binding protein were analyzed as targets of GSK-3beta activity, overexpression of wild-type GSK-3beta suppressed AP1-mediated transcription and activated CRE-mediated transcription. Overexpression of GSK-3betadelta9 caused an (80-fold) increase in CRE-mediated transcription, which was further amplified (up to 130-fold) by combining GSK-3betadelta9 overexpression with the suppression of Jun activity. This study also demonstrated for the first time that expression of constitutively active GSK-3betadelta9 results in the phosphorylation of CRE-binding protein on serine 129 and enhancement of CRE-mediated transcription in intact cell nuclei.
-
Keloid fibroproliferation appears to be influenced by epithelial-mesenchymal interactions between keloid keratinocytes (KKs) and keloid fibroblasts (KFs). Keloid and normal fibroblasts exhibit accelerated proliferation and collagen I and III production in co-culture with KKs compared with single cell culture or co-culture with normal keratinocytes. ERK and phosphatidylinositol 3-kinase (PI3K) pathway activation has been observed in excessively proliferating KFs in co-culture with KKs. ⋯ These data strongly suggest that synchronous activation of both the ERK and PI3K pathways is essential for collagen I-III and laminin beta2 production. These pathways additionally appear to affect the side chain attachments of fibronectin. Modulation of these pathways may suggest a direction for keloid therapy.
-
Hyperoxia induces growth arrest, apoptosis, necrosis, and morphological changes (spreading and adhesion) in various types of cells. The mechanism of hyperoxia-induced cell growth arrest has not been well elucidated, especially in macrophages. One possible mechanism is a role of cell adhesion in hyperoxia-induced cell cycle arrest. ⋯ These effects of hyperoxia were attenuated under low adhesion conditions, suggesting a role for integrin-dependent signaling. The induction of p21Cip1 and activation of retinoblastoma protein occurred via a p53-independent mechanism. These results suggest that adhesion-dependent pathways are required for hyperoxia-induced cell cycle arrest in macrophages.
-
The mitochondrial respiratory chain is a major source of reactive oxygen species (ROS) under pathological conditions including myocardial ischemia and reperfusion. Limitation of electron transport by the inhibitor rotenone immediately before ischemia decreases the production of ROS in cardiac myocytes and reduces damage to mitochondria. We asked if ROS generation by intact mitochondria during the oxidation of complex I substrates (glutamate, pyruvate/malate) occurred from complex I or III. ⋯ ROS are produced from complex I by the NADH dehydrogenase located in the matrix side of the inner membrane and are dissipated in mitochondria by matrix antioxidant defense. However, in submitochondrial particles devoid of antioxidant defense ROS from complex I are available for detection. In mitochondria, complex III is the principal site for ROS generation during the oxidation of complex I substrates, and rotenone protects by limiting electron flow into complex III.
-
Diacylglycerol kinase alpha (DAGK alpha), like all type I DAGKs, has calcium regulatory motifs that act as negative regulators of enzyme activity and localization. Accordingly, DAGK alpha is activated by phospholipase C-coupled receptors in a calcium-dependent manner. One of the first functions attributed to DAGK alpha in lymphocytes was that of regulating interleukin 2-induced cell cycle entry. ⋯ Our results demonstrate that, in vivo, the increase in cellular levels of PI3K products is sufficient to induce DAGK alpha activation, allowing DAGK alpha relocation to the intact lymphocyte plasma membrane. This activation is isoform-specific, because other type I DAGKs are not subject to this type of regulation. These studies are the first to describe a pathway in which, in the absence of receptor-regulated calcium increase, DAGK alpha activation and membrane localization is a direct consequence of PI3K activation.