INDUCTION OF C-FOS EXPRESSION FOLLOWING STIMULATION OF PULMONARY NEUROENDOCRINE CELL-PROLIFERATION BY ALTERATIONS IN CO2 O-2 CONCENTRATION/

Pulmonary neuroendocrine (PNE) cells were harvested and cultivated fro m peripheral lung tissue of 15 day old fetal hamsters under selective growth conditions, including a 10% CO2 atmosphere. Following 24 h of s erum starvation under 10% CO2, PNE cells placed in a 5% CO2 atmosphere failed to proliferate over the next 24 h, while cells kept at 10% CO2 showed a 2.7-fold increase in cell number. Addition of nicotine to th e cell culture medium resulted in an additional concentration-dependen t increase in cell number under a 10% CO2 atmosphere, while nicotine d id not stimulate the proliferation of cells maintained at 5% CO2. The nicotinic receptor antagonist hexamethonium completely blocked the sti mulatory effect of nicotine on cell growth. As a first step towards de termining the molecular mechanisms regulating the mitogenic stimulatio n of PNE cells by alterations in CO2/O-2 and nicotine, cells that had been serum starved under a 10% CO2 atmosphere for 24 h were removed fr om the incubator and either left untreated or treated with 1 mu M nico tine under ambient air. The cells were then returned to either a 5% or 10% CO2 atmosphere. Removal of the cells from a 10% CO2 environment a nd subsequent reintroduction to a high CO2 concentration resulted in a 3- to 4-fold increase in c-Sos RNA expression within 15-30 min upon r eturn to the cell culture incubator. c-fos RNA levels their decreased back to control values by 1 h. Reintroduction into a 5% CO2 atmosphere , which failed to stimulate cell growth in the proliferation assay, ca used only a 2-fold increase in the levels of c-fos transcripts. The CO 2-mediated increases in c-Sos transcripts were observed both in the pr esence and absence of nicotine, suggesting that the effects of nicotin e were mediated through a fos-independent pathway. Neither the alterat ions in CO2/O-2 concentration or treatment with nicotine altered the l evels of c-myc or c-jun gene transcripts. Nicotine thus acts indirectl y but synergistically with high CO2 concentrations to stimulate PNE ce ll proliferation.