Phosphorylation of epidermal growth factor receptor at serine 1047 by MAP kinase-activated protein kinase-2 in cultured lung epithelial cells treated with flagellin

The impact of nitric oxide on HER family post-translational modification and downstream signaling in cancer

The human epidermal growth factor receptor (HER) family consists of four members, activated by two families of ligands. They are known for mediating cell-cell interactions in organogenesis, and their deregulation has been associated with various cancers, including breast and esophageal cancers. In particular, aberrant epidermal growth factor receptor (EGFR) and HER2 signaling drive disease progression and result in poorer patient outcomes. Nitric oxide (NO) has been proposed as an alternative activator of the HER family and may play a role in this aberrant activation due to its ability to induce s-nitrosation and phosphorylation of the EGFR. This review discusses the potential impact of NO on HER family activation and downstream signaling, along with its role in the efficacy of therapeutics targeting the family.

Regulation of epidermal growth factor receptor expression and morphology of lung epithelial cells by interleukin-1β

Accumulating evidences suggested that the overactivation of epidermal growth factor receptor (EGFR) was involved in the development of adult respiratory distress syndrome and pulmonary fibrosis. Elucidation of the mechanisms that regulate EGFR residence on the plasma membrane during inflammatory lung conditions is important for identifying potential therapies. We have demonstrated that flagellin phosphorylated EGFR at Ser1047 and induced transient EGFR internalization. In this study, we examined the molecular pathway and effect of interleukin 1 beta (IL-1β) on EGFR in alveolar epithelial cells. Treatment of A549 cells with IL-1β induced the activation of p38 mitogen-activated protein kinase (MAP kinase) and MAP kinase-activated protein kinase-2 (MAPKAPK-2), as well as EGFR phosphorylation at serine 1047. Both MAPKAPK-2 activation and EGFR phosphorylation were inhibited by SB203580, a p38 MAP kinase inhibitor. In addition, MK2a inhibitor (a MAPKAPK-2 inhibitor) suppressed EGFR phosphorylation. Assessment of the biotinylation of cell surface proteins indicated that IL-1β induced EGFR internalization. Furthermore, long-term treatment of A549 cells with IL-1β caused morphological changes and loss of cell-cell contact. Moreover, IL-1β augmented the effect of transforming growth factor beta 1 on the epithelial-mesenchymal transition. These results suggested that IL-1β regulates EGFR functions and induces morphological changes of alveolar epithelial cells.

Increased expression of EGR1 and KLF4 by polysulfide via activation of the ERK1/2 and ERK5 pathways in cultured intestinal epithelial cells

Sodium trisulfide (Na₂S₃) releases hydrogen polysulfide (H₂S_n) and is useful for the investigation of the effects of H₂S_n on the cell functions. In the present study, we first examined the effects of Na₂S₃ on the gene expression of IEC-6 cells, a rat intestinal epithelial cell line. Microarray analysis and reverse transcription-polymerase chain reaction analysis revealed that Na₂S₃ increased the gene expression of early growth response 1 (EGR1) and Kruppel-like transcription factor 4 (KLF4). It was interesting that U0126, an inhibitor of the activation of extracellular signal-regulated kinase 1 (ERK1), ERK2, and ERK5, inhibited the Na₂S₃-induced gene expression of EGR1 and KLF4. Na₂S₃ activated ERK1 and ERK2 (ERK1/2) within 15 min. In addition to ERK1/2, Na₂S₃ activated ERK5. We noticed that the electrophoretic mobility of ERK5 was decreased after Na₂S₃ treatment. Phos-tag analysis and in vitro dephosphorylation of the cell extracts indicated that the gel-shift of ERK5 was due to its phosphorylation. The gel-shift of ERK5 was inhibited completely by both U0126 and ERK5-IN-1, a specific inhibitor of ERK5. From these results, we concluded that the gel-shift of ERK5 was induced through autophosphorylation by activated ERK5 after Na₂S₃ treatment. The present study suggested that H₂S_n affected various functions of intestinal epithelial cells through the activation of the ERK1/2 and ERK5 pathways.

Adenovirus early region 3 RIDα protein limits NFκB signaling through stress-activated EGF receptors

The host limits adenovirus infections by mobilizing immune systems directed against infected cells that also represent major barriers to clinical use of adenoviral vectors. Adenovirus early transcription units encode a number of products capable of thwarting antiviral immune responses by co-opting host cell pathways. Although the EGF receptor (EGFR) was a known target for the early region 3 (E3) RIDα protein encoded by nonpathogenic group C adenoviruses, the functional role of this host-pathogen interaction was unknown. Here we report that incoming viral particles triggered a robust, stress-induced pathway of EGFR trafficking and signaling prior to viral gene expression in epithelial target cells. EGFRs activated by stress of adenoviral infection regulated signaling by the NFκB family of transcription factors, which is known to have a critical role in the host innate immune response to infectious adenoviruses and adenovirus vectors. We found that the NFκB p65 subunit was phosphorylated at Thr254, shown previously by other investigators to be associated with enhanced nuclear stability and gene transcription, by a mechanism that was attributable to ligand-independent EGFR tyrosine kinase activity. Our results indicated that the adenoviral RIDα protein terminated this pathway by co-opting the host adaptor protein Alix required for sorting stress-exposed EGFRs in multivesicular endosomes, and promoting endosome-lysosome fusion independent of the small GTPase Rab7, in infected cells. Furthermore RIDα expression was sufficient to down-regulate the same EGFR/NFκB signaling axis in a previously characterized stress-activated EGFR trafficking pathway induced by treatment with the pro-inflammatory cytokine TNF-α. We also found that cell stress activated additional EGFR signaling cascades through the Gab1 adaptor protein that may have unappreciated roles in the adenoviral life cycle. Similar to other E3 proteins, RIDα is not conserved in adenovirus serotypes associated with potentially severe disease, suggesting stress-activated EGFR signaling may contribute to adenovirus virulence.

Cytotoxic activity of the MK2 inhibitor CMPD1 in glioblastoma cells is independent of MK2

MAPK-activated protein kinase 2 (MK2) is a checkpoint kinase involved in the DNA damage response. MK2 inhibition enhances the efficacy of chemotherapeutic agents; however, whether MK2 inhibition alone, without concurrent chemotherapy, would attenuate survival of cancer cells has not been investigated. CMPD1 is a widely used non-ATP competitive inhibitor that prevents MK2 phosphorylation. We employed CMPD1 together with MK2 knock-down and ATP-competitive MK2 inhibitor III (MK2i) in a panel of glioblastoma cells to assess whether MK2 inhibition could induce cancer cell death. While CMPD1 was effective at selective killing of cancer cells, MK2i and MK2 knock-down had no effect on viability of glioblastoma cells. CMPD1 treatment induced a significant G2/M arrest but MK2i-treated cells were only minimally arrested at G1 phase. Intriguingly, at doses that were cytotoxic to glioblastoma cells, CMPD1 did not inhibit phosphorylation of MK2 and of its downstream substrate Hsp27. These results suggest that CMPD1 exhibits cytotoxic activity independently of MK2 inhibition. Indeed, we identified tubulin as a primary target of the CMPD1 cytotoxic activity. This study demonstrates how functional and mechanistic studies with appropriate selection of test compounds, combining genetic knock-down and pharmacological inhibition, coordinating timing and dose levels enabled us to uncover the primary target of an MK2 inhibitor commonly used in the research community. Tubulin is emerging as one of the most common non-kinase targets for kinase inhibitors and we propose that potential tubulin-targeting activity should be assessed in preclinical pharmacology studies of all novel kinase inhibitors.

Desensitization by different strategies of epidermal growth factor receptor and ErbB4

Four transmembrane tyrosine kinases constitute the ErbB protein family: epidermal growth factor receptor (EGFR) or ErbB1, ErbB2, ErbB3, and ErbB4. In general, the structure and mechanism of the activation of these members are similar. However, significant differences in homologous desensitization are known between EGFR and ErbB4. Desensitization of ligand-occupied EGFR occurs by endocytosis, while that of ErbB4 occurs by selective cleavage at the cell surface. Because ErbB4 is abundantly expressed in neurons from fetal to adult brains, elucidation of the desensitization mechanism is important to understand neuronal development and synaptic functions. Recently, it has become clear that heterologous desensitization of EGFR and ErbB4 are induced by endocytosis and cleavage, respectively, similar to homologous desensitization. It has been reported that heterologous desensitization of EGFR is induced by serine phosphorylation of EGFR via the p38 mitogen-activated protein kinase (p38 MAP kinase) pathway in various cell lines, including alveolar epithelial cells. In contrast, the protein kinase C pathway is involved in ErbB4 cleavage. In this review, we will describe recent advances in the desensitization mechanisms of EGFR and ErbB4, mainly in alveolar epithelial cells and hypothalamic neurons, respectively.