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 epitheliall 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 perinuclear area of control cells. Upon cigarette smoke exposure, Scavenger Receptor B1 first translocated to the cell surface (within the first 12 h of exposure) and then cell levels (protein and mRNA levels) decreased significantly at 24 h. 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.