Epidermal growth factor receptor exposed to cigarette smoke is aberrantly activated and undergoes perinuclear trafficking.

Exposure to hydrogen peroxide (H2O2), one of the reactive oxidants in the gas phase of cigarette smoke (CS), induces aberrant phosphorylation of the epidermal growth factor receptor (EGFR), resulting in the lack of ubiquitination by c-Cbl, and impaired degradation. EGFR activation without the feedback regulation of normal degradation leads to uncontrolled cell growth and tumor promotion. Using immunoprecipitation, immunoblotting, and confocal microscopy, we now demonstrate that the pattern of EGFR activation by CS is similar to H2O2. We found that exposure of human airway epithelial cells to CS, as with exposure to H2O2, not only results in an increase in EGFR activation over time, but the EGFR activated by H2O2 or CS is neither ubiquitinated nor subsequently degraded due to its inability to bind the E3 ubiquitin ligase, c-Cbl, either directly or indirectly via the Grb2 adapter protein. Moreover, the stabilized H2O2- and CS-activated EGFR remains plasma membrane-bound, while a population of the receptor is trafficked to a perinuclear region. Concomitantly, CS exposure results in the activation of downstream Akt and ERK1/2 survival and proliferation pathways. Therefore, exposure to CS, like exposure to H2O2, results in prolonged signaling by the EGFR and may contribute to uncontrolled lung cell growth.

Cigarette smoke exposure causes changes in Scavenger Receptor B1 level and distribution in lung cells.

Scavenger Receptor B1 has been shown to play a prominent role in the uptake and delivery of vitamin E from HDL and is likely involved in regulating vitamin E in the lung. We have previously demonstrated that lung Scavenger Receptor B1 levels (protein and mRNA) are modulated by cigarette smoke in mice and this was accompanied by changes in lung vitamin E. To further characterize the molecular mechanism(s) involved in this process, human alveolar epithelial cells were exposed to cigarette smoke and Scavenger Receptor B1 cellular levels and distribution were assessed. Results demonstrated that Scavenger Receptor B1 localizes in patches on the cellular membrane and in the per nuclear area of control cells. Upon cigarette smoke exposure, Scavenger Receptor B1 first translocated to the cell surface (within the first 12h of exposure) and then cell levels (protein and mRNA levels) decreased significantly at 24h. This decline was accompanied by increased Scavenger Receptor B1 ubiquitination which may explain the decrease in the protein levels. Cigarette smoke induced changes in both sub-cellular redistribution and ubiquitination of Scavenger Receptor B1 together with our previous in vivo data provides evidence that cigarette smoke exposure may alter lung's ability to control its tocopherol levels.