MAPK3 and diabetes mellitus: Reduced level of transcription factor FOXO1 and β2 arrestin, along with increased ERK1/2 in CF cells. FOXO1 reduction is linked to loss of CFTR function and increased after insulin-like growth factor 1 (IGF-1) administration. Reduced FOXO1 may explain insulin insensitivity in CF, with IGF-1 constituting a potential treatment of CF-related diabetes