Tobacco smoke control of mucin production in lung cells requires oxygen radicals AP-1 and JNK

In smokers' lungs, excessive mucus clogs small airways, impairing respiration and promoting recurrent infection. A breakthrough in understanding this pathology was the realization that smoke could directly stimulate mucin synthesis in lung epithelial cells and that this phenomenon was dependent on the cell surface receptor for epidermal growth factor, EGFR. Distal steps in the smoke-triggered pathway have not yet been determined. We report here that the predominant airway mucin (MUC5AC) undergoes transcriptional up-regulation in response to tobacco smoke; this is mediated by an AP-1-containing response element, which binds JunD and Fra-2. These transcription factors require phosphorylation by upstream kinases JNK and ERK, respectively. Whereas ERK activation results from the upstream activation of EGFR, JNK activation is chiefly EGFR-independent. Our experiments demonstrated that smoke activates JNK via a Src-dependent, EGFR-independent signaling cascade initiated by smoke-induced reactive oxygen species. Taken together with our earlier results, these data indicate that the induction of mucin by smoke is the combined effect of mutually independent, reactive oxygen species activation of both EGFR and JNK.

Mechanisms by which gram-positive bacteria and tobacco smoke stimulate mucin induction through the epidermal growth factor receptor (EGFR)

Mucin, the major macromolecular component of mucus, is generally considered to be a protective substance. When overproduced in a variety of lung diseases, however, mucin gives rise to clinical problems such as airway obstruction and recurrent infection. Our approach to identifying drug targets for the control of mucin overproduction is the analysis of cellular signalling pathways linking stimuli in the diseased lung to mucin transcription. Here we show that mucin transcription in response to both gram-positive bacteria and tobacco smoke is mediated through activation of the epidermal growth factor receptor (EGFR). The mode of activation of EGFR in response to bacterial lipoteichoic acid involves cleavage of the transmembrane ligand HBEGF by ADAM 10, whereas the activation of EGFR in response to smoke involves cleavage of amphiregulin by ADAM 17.

Control of mucin transcription by diverse injury-induced signaling pathways

Mucin production is an evolutionarily ancient defense mechanism that is retained in mammals and operates at all mucosal surfaces to protect the host against pathogens and irritants. As in lower organisms, the mammalian mucosa (epithelium) produces mucin in response to diverse insults. Our studies aim to understand the intracellular signaling and gene regulation mechanisms mediating mucin production in response to clinically important insults. To date, we find that the signaling pathway triggered by each type of insult is distinct. Relatively common, however, is the involvement of the protein tyrosine kinase c-Src, the MAP kinase kinase MEK 1/2, and the transcription factor NF-kappaB. Basbaum C, Lemjabbar H, Longphre M, Li D, Gensch E, McNamara N. Control of mucin transcription by diverse injury-induced signaling pathways.

A C. elegans mutant that lives twice as long as wild type

We have found that mutations in the gene daf-2 can cause fertile, active, adult Caenorhabditis elegans hermaphrodites to live more than twice as long as wild type. This lifespan extension, the largest yet reported in any organism, requires the activity of a second gene, daf-16. Both genes also regulate formation of the dauer larva, a developmentally arrested larval form that is induced by crowding and starvation and is very long-lived. Our findings raise the possibility that the longevity of the dauer is not simply a consequence of its arrested growth, but instead results from a regulated lifespan extension mechanism that can be uncoupled from other aspects of dauer formation. daf-2 and daf-16 provide entry points into understanding how lifespan can be extended.