Asbestos-mediated CREB phosphorylation is regulated by protein kinase A and extracellular signal-regulated kinases 1/2

Abstract

Asbestos is a ubiquitous, naturally occurring fiber that has been linked to the development of malignant and fibrotic lung diseases. Asbestos exposure leads to apoptosis, followed by compensatory proliferation, yet many of the signaling cascades coupled to these outcomes are unclear. Because CREs (Ca2+/cAMP-response elements) are found in the promoters of many genes important for regulation of proliferation and apoptosis, CREB (CRE binding protein) is likely to play an important role in the development of asbestos-mediated lung injury. To explore this possibility, we tested the hypotheses that asbestos exposure leads to CREB phosphorylation in lung epithelial cells and that protein kinase A (PKA) and extracellular signal-regulated kinases 1/2 (ERK1/2) are central regulators of the CREB pathway. Persistent CREB phosphorylation was observed in lung sections from mice following inhalation of crocidolite asbestos. Exposure of C10 lung epithelial cells to crocidolite asbestos led to rapid CREB phosphorylation and apoptosis that was decreased by the inhibition of PKA or ERK1/2 using the specific inhibitors H89 and U0126, respectively. Furthermore, crocidolite asbestos selectively induced a sustained increase in MAP kinase phosphatase-1 mRNA and protein. Silencing CREB protein dramatically reduced asbestos-mediated ERK1/2 phosphorylation, yet significantly increased the number of cells undergoing asbestos-induced apoptosis. These data reveal a novel and selective role for CREB in asbestos-mediated signaling through pathways regulated by PKA and ERK1/2, further providing evidence that CREB is an important regulator of apoptosis in asbestos-induced responses of lung epithelial cells.

Activated cAMP Response Element Binding Protein Is Overexpressed in Human Mesotheliomas and Inhibits Apoptosis

“…43 Increased MKP1 mRNA levels by asbestos is puzzling in LP9 cells but may represent a compensatory response to increases in phosphorylated mitogen-activated protein kinase by asbestos in these and other cell types. 25,28,29,31,42 Other recent data support additional roles of activated CREB in other tumor types. For example, CREB levels are elevated in blast cells from patients with acute myeloid leukemia, resulting in abnormal proliferation and survival of myeloblast cells in vitro and in vivo via a cyclin A1 pathway.…”

“…35 We previously demonstrated activation of CREB by asbestos in murine lung epithelial cells via EGFR, PKA, and ERK1/2 cascades. 31 However, in human mesothelial cells, ERK1/2, CaM kinase II, and PKC inhibitors had no effect on asbestos-induced CREB activation, suggesting that CREB signaling may be cell type-and/or species-dependent. Our findings here show that CREB activation by asbestos either alone or in conjunction with other signaling pathways activated by asbestos may augment the development of mesothelioma.…”

Alterations in Gene Expression in Human Mesothelial Cells Correlate with Mineral Pathogenicity

“…In addition, trends in production of VEGF, a known important angiogenic peptide and independent prognostic factor in human mesotheliomas (33), were observed. We have recently shown that an extracellular signal-related CREB pathway in C10 lung epithelial cells modulates apoptosis after asbestos exposure (34), and recent studies are focusing on the effects of silencing CREB or ATF3 on other functional and phenotypic changes in human mesothelial and mesothelioma cells (A. Shukla and colleagues, unpublished data).…”

A Protein Kinase Cδ-Dependent Protein Kinase D Pathway Modulates ERK1/2 and JNK1/2 Phosphorylation and Bim-Associated Apoptosis by Asbestos

“…40 Results showed that increased apoptosis by asbestos was unaffected by Bay11-7082 at 5 or 10 mol/L ( Figure 6D). Since we have previously used ERK1/2 small molecule inhibitors, including U0126, to show that the duration of ERK1/2 signaling by asbestos determines proliferative versus apoptopic responses in C10 cells, 17,42 experiments using UO126 were not repeated here.…”

“…8 -10 Asbestos-induced signaling mechanisms governing these cell responses appear to involve a broad variety of cascades including the mitogen-activated protein kinases (MAPK), 3,7,11,12 nuclear factor-B (NF-B), 9,13,14 and the protein kinase (PK)C 10,12,15,16 and A families. 17 A critical signaling protein involved in asbestos signaling is PKC␦, which is known to be activated in bronchiolar and alveolar epithelial cells in vivo and in vitro 10,12,16 via increased formation of diacylglycerol. 18 We have shown that PKC␦ governs apoptosis via an oxidant-dependent mitochondrial pathway after exposure of lung epithelial cells to asbestos fibers.…”