Lung cancer is the leading cause of
cancer-related death worldwide.
Hypoxia is known to increase
cancer cell migration and invasion. We have previously reported that
hypoxia induces epithelial-mesenchymal transition (EMT) in
lung cancer cells. However, it is unknown whether
hypoxia promotes
lung cancer cell migration and invasion via EMT and whether
cyclic AMP (
cAMP) dependent protein kinase (PKA) plays a role in this process. We found that
hypoxia increased PKA activity and induced
mRNA and
protein expression of PKA catalytic subunit α (PKACA), and regulatory subunits R1A and R1B. Knockdown of HIF-1/2α prevented
hypoxia-mediated induction of PKACA
mRNA expression and PKA activity. Inhibition of PKA activity with chemical inhibitors prevented EMT induced by
hypoxia and
tumor growth factor β1. However, activation of PKA by
forskolin and 8-Br-cAMP did not induce EMT. Furthermore, treatment with
H89 and knockdown of PKACA prevented
hypoxia-mediated, EMT, cell migration, and invasion, whereas overexpression of mouse PKACA rescued
hypoxia-mediated migration and invasion in PKACA deficient
cancer cells. Our results suggest that
hypoxia enhances PKA activity by upregulating PKA gene expression in a HIF dependent mechanism and that PKA plays a key role in
hypoxia-mediated EMT, migration, and invasion in
lung cancer cells.