Model of PR-scaffolding interactions. Previously reported interactions between PR (PxxP, proline-rich domain) and/or ER (phospho-tyrosine 537) and c-Src (SH3 domain with PR, SH2 domain with ER), as well as interactions between PR (ERID, estrogen receptor interaction domain) and ER (LBD, ligand-binding domain) have been shown to be necessary for progesterone-induced c-Src/MAPK activation [23–25,36,37]. Additionally, complex formation between PR (CD domain) and MEK1 (D domain) may be necessary for MEK1 docking and subsequent PR posttranslational modification and activation.