Other effects of smoking on cell-specific gene expression included: (1) transcriptional regulation (ATF4 - increased in BC; PAX5, HES1 - decreased in mucin-producing cells); (2) growth factors (CTGF, IL33 - increased in BC); (3) receptors (CD55 - increased in mucous-producing cells; PIGR – decreased in intermediate, club and ciliated cells); (4) ionic balance (CLCA2 – decreased in BC; AQP3 – increased in intermediate cells); and (5) signal transduction (ERRFI1 - increased in intermediate and club cells; DKK3 - increased in BC; Fig. 4b, Supplemental Tables S5 and S6). Here, ERRFI1 is linked to breast cancer.