When stimulated by its hormone, gastrin-releasing peptide, GRPR triggers cell proliferation typically seen in lung cancer. The Pittsburgh-based research team also discovered that nicotine found in cigarettes stimulates expression of the GRPR gene in lung cells. This study also validates previous population studies suggesting that women are at substantially increased risk of smoking-related lung cancer. The scientists looked at normal lung tissue samples from 38 women and 40 men, including 58 patients with lung cancer. The difference between the sexes is related to the location of the GRPR gene on the X chromosome, according to the investigators.
Women have two X chromosomes, whereas men have one copy.
Normally in a woman, genes are inactivated on one of the X chromosomes. However, both copies of the GRPR gene are active in women. Women may be at increased risk because they have two copies of the GRPR gene that are inducible by nicotine, whereas men only have one nicotine-inducible copy. Another possibility is that one GRPR gene in women is chronically active, even before exposure to nicotine. Because they did not measure exposure to passive smoke, the scientists could not distinguish the role that such exposure might play in activating the GRPR gene in women.