Persistent Nicotine Treatment Potentiates Amplification of the Dihydrofolate Reductase Gene in Rat Lung Epithelial Cells as a Consequence of Ras Activation

Abstract

Although nicotine has been suggested to promote lung carcinogenesis, the mechanism of its action in this process remains unknown. The present investigation demonstrates that the treatment of rat lung epithelial cells with nicotine for various periods differentially mobilizes multiple intracellular pathways. Protein kinase C and phosphoinositide 3-OH-kinase are transiently activated after the treatment. Also, Ras and its downstream effector ERK1/2 are activated after long term exposure to nicotine. The activation of Ras by nicotine treatment is responsible for the subsequent perturbation of the methotrexate (MTX)-mediated G 1 cell cycle restriction as well as an increase in production of reactive oxygen species. When p53 expression is suppressed by introducing E6, persistent exposure to nicotine enables dihydrofolate reductase gene amplification in the presence of methotrexate (MTX) and the formation of the MTX-resistant colonies. Altering the activity of phosphoinositide 3-OH-kinase has no effect on dihydrofolate reductase amplification. However, the suppression of protein kinase C dramatically affects the colony formation in soft agar. Thus, our data suggest that persistent exposure to nicotine perturbs the G 1 checkpoint and causes DNA damage through the increase of the production of reactive oxygen species. However, a third element rendered by loss of p53 is required for the initiation of the process of gene amplification. Under p53-deficient conditions, the establishment of a full oncogenic transformation, in response to long term nicotine exposure, is achieved through the cooperation of multiple signaling pathways.

Nicotine-induced memory impairment by increasing brain oxidative stress

“…The present findings support the hypothesis that decreased SOD activity can lead to an accumulation of H 2 O 2 which, in the absence of a simultaneous increase in GPX activity, could increase the Fenton reaction, leading to the stimulation of lipid peroxidation and protein oxidation resulting, in cellular damage [44][45][46]. Also, we observed a significant increase in ROS production in rat temporal cortex which is comparable to other previously reported data [47,48].…”

Modulation of Intracellular Signaling Pathways to Induce Apoptosis in Prostate Cancer Cells

“…Samples were incubated for 10 min at room temperature and analyzed immediately by a flow cytometer (57).…”

Transgenerational Effects of Maternal Nicotine Exposure During Gestation and Lactation on the Respiratory System

“…This can be achieved in two ways: by having a direct effect on cells and/or by reducing the nutrient supply to the fetus during gestation and lactation. It has been shown that long-term nicotine exposure results in a predisposition for genetic instability [22,33,34]. This may result in changes in the genetic "program" that controls lung development, maintenance of lung structure and aging of lung tissue, which may render the lungs more prone to disease.…”

“…It has been shown that long-term nicotine exposure results in a predisposition for the induction of genetic instability [32,34,45]. Gene amplification is a hallmark of gene instability.…”