STAT1 and STAT3 activation by oxidative stress in A431 cells involves Src-dependent EGF receptor transactivation

Different cellular signal transduction cascades are affected by environmental stressors (UV-radiation, gamma-irradiation, hyperosmotic conditions, oxidants). In this study, we examined oxidative stress-evoked signal transduction pathways leading to activation of STATs in A431 carcinoma cells. Oxidative stress, initiated by addition of H2O2 (1-2 mM) to A431 cells, activates STAT3 and, to a lesser extent, STAT1 in dose- and time-dependent manner. Maximum phosphorylation levels were observed after a 2 minutes stimulation at 1-2 mM H2O2. Phosphorylation was blocked by AG1478, a pharmacological inhibitor of the epidermal growth factor receptor tyrosine kinase, implicating intrinsic EGF receptor tyrosine kinase in this process. Consistent with this observation, H2O2-stimulated EGFR tyrosine phosphorylation was abolished by specific Src kinase family inhibitor CGP77675, implicating Src in H2O2-induced EGFR activation. An essential role for Src and JAK2 in STATs activation was suggested by three findings. 1. Src kinase family inhibitor CGP77675 blocked STAT3 and STAT1 activation by H2O2 in a concentration-dependent manner. 2. In Src-/-fibroblasts, activation of both STAT3 and STAT1 by H2O2 was significantly attenuated. 3. Inhibiting JAK2 activity with the specific inhibitor AG490 reduced the level of H2O2-induced STAT3 phosphorylation, but not STAT1 in A431 cells. These data show essential roles for Src and JAK2 inactivation of STAT3. In contrast, H2O2-mediated activation of STAT1 requires only Src kinase activity. Herein, we postulate also that H2O2-induced STAT activation in carcinoma cells involves Src-dependent EGFR transactivation.     

H2O2-induced activation of transcription factors STAT1 and STAT3: the role of EGF receptor and tyrosine kinase JAK2

Reactive oxygen species initiate multiple signal transduction pathways including tyrosine kinase signaling. Here, we demonstrate tyrosine phosphorylation of EGF receptor, STAT3, and, to a lesser extent, STAT1 upon H2O2 treatment of HER14 cells (NIH3T3 fibroblasts transfected with full-length EGF receptor). Maximum phosphorylation levels were observed in 5 min of stimulation at 1-2 mM H2O2. It has been shown that the intrinsic EGF-receptor tyrosine kinase is responsible for the receptor phosphorylation upon H2O2 stimulation. STAT3 and STAT1 activation in HER14 cells was demonstrated to depend on EGF receptor kinase activity, rather than JAK2 activity, while in both K721A and CD126 cells (NIH3T3 transfected with kinase-dead EGF receptor, and EGF receptor lacking major autophosphorylation sites, respectively) STAT1 and STAT3 tyrosine phosphorylation requires JAK2 kinase activity. Furthermore, STAT3 is constitutively phosphorylated in K721A and CD126 cells, and STAT1 H2O2-stimulated activation in these cells is much more prominent than in HER14. In all the cell lines used, Src-kinase activity was demonstrated to be unnecessary for ROS-initiated phosphorylation of STATs. Herein, we postulate that EGF receptor plays a role in H2O2-induced STAT activation in HER14 cells. Our data also prompted a hypothesis of constitutive inhibition of JAK2-dependent STAT activation in this cell line.     

JAK/STAT信号转导通路与淋巴瘤的形成

JAK/STAT信号转导通路的异常激活在多种淋巴瘤的发生发展中发挥重要作用. 该信号通路的抑制剂在淋巴瘤的靶向治疗中具有良好的应用前景．本文对JAK/STAT信号通路与淋巴瘤发生、发展的最新研究进展进行综述,重点介绍该信号通路中各种JAK激酶及STAT分子的异常突变类型,以及它们在各类淋巴瘤形成中的作用、调控机制及其靶向治疗策略,旨在为该信号通路在淋巴瘤发生发展中的影响及作用机制的进一步研究提供借鉴．     

Akt/protein kinase B isoforms are differentially regulated by epidermal growth factor stimulation

Overexpression of epidermal growth factor receptor (EGFR) in certain cancers is well established. There is growing evidence that epidermal growth factor (EGF) activates Akt/protein kinase B (PKB) in a phosphoinositide 3-OH kinase (PI3K)-dependent manner, but it is not yet clear which Akt isoforms are involved in this signal transduction pathway. We investigated the functional regulation of three Akt isoforms, Akt1/PKBalpha, Akt2/PKBbeta, and Akt3/PKBgamma, in esophageal cancer cells where EGFR is frequently overexpressed. Upon EGF simulation, phosphorylation of Akt1 at the Ser-473 residue was remarkably induced. This result was corroborated by in vitro Akt kinase assays using glycogen synthase kinase 3beta as the substrate. PI3K inhibitors, wortmannin or LY294002, significantly blocked the Akt kinase activity induced by EGF. Akt2 activity was evaluated by electrophoretic mobility shift assays. Robust activation of Akt2 by EGF was observed in some cell lines in a PI3K-dependent manner. EGF-induced Akt3 activation was demonstrated by Ser-472 phosphorylation of Akt3 but in a restrictive fashion. In aggregate, EGF-mediated activation of Akt isoforms is overlapping and distinctive. The mechanism by which EGFR recruits the PI3K/Akt pathway was in part differentially regulated at the level of Ras but independent of heterodimerization of EGFR with either ErbB2 or ErbB3 based upon functional dissection of pathways in esophageal cancer cell lines.     

Prolactin-stimulated activation of ERK1/2 mitogen-activated protein kinases is controlled by PI3-kinase/Rac/PAK signaling pathway in breast cancer cells

There is strong evidence that deregulation of prolactin (PRL) signaling contributes to pathogenesis and chemoresistance of breast cancer. Therefore, understanding cross-talk between distinct signal transduction pathways triggered by activation of the prolactin receptor (PRL-R), is essential for elucidating the pathogenesis of metastatic breast cancer.In this study, we applied a sequential inhibitory analysis of various signaling intermediates to examine the hierarchy of protein interactions within the PRL signaling network and to evaluate the relative contributions of multiple signaling branches downstream of PRL-R to the activation of the extracellular signal-regulated kinases ERK1 and ERK2 in T47D and MCF-7 human breast cancer cells.Quantitative measurements of the phosphorylation/activation patterns of proteins showed that PRL simultaneously activated Src family kinases (SFKs) and the JAK/STAT, phosphoinositide-3 (PI3)-kinase/Akt and MAPK signaling pathways. The specific blockade or siRNA-mediated suppression of SFK/FAK, JAK2/STAT5, PI3-kinase/PDK1/Akt, Rac/PAK or Ras regulatory circuits revealed that (1) the PI3-kinase/Akt pathway is required for activation of the MAPK/ERK signaling cascade upon PRL stimulation; (2) PI3-kinase-mediated activation of the c-Raf-MEK1/2-ERK1/2 cascade occurs independent of signaling dowstream of STATs, Akt and PKC, but requires JAK2, SFKs and FAK activities; (3) activated PRL-R mainly utilizes the PI3-kinase-dependent Rac/PAK pathway rather than the canonical Shc/Grb2/SOS/Ras route to initiate and sustain ERK1/2 signaling. By interconnecting diverse signaling pathways PLR may enhance proliferation, survival, migration and invasiveness of breast cancer cells.