Binding of IFITM1 enhances the inhibiting effect of caveolin-1 on ERK activation.

Interferon-induced transmembrane protein 1 (IFITM1) is an essential mediator of interferon-g-induced antiproliferation. Here, we reported the interaction between IFITM1 and caveolin-1 (CAV-1), and their inhibitory regulatory function on extracellular signal-regulated kinase (ERK). The immunofluorescence staining result showed that IFITM1 localized in caveolae of the plasma membrane and could interact with CAV-1. Deletion mutagenesis clearly revealed that the hydrophobic transmembrane domains were responsible for the interaction between IFITM1 and CAV-1. It has been reported that CAV-1 has inhibitory effect on the phosphorylation of ERK, and subsequently ERK-mediated transcription. Our study showed the interaction of IFITM1- and CAV-1-enhanced CAV-1's inhibitory effect on ERK activation, whereas the IFITM1 did not activate ERK directly. This inhibitory effect was further confirmed by knocking down the endogenous CAV-1 using RNA interference. These results revealed that the interaction between IFITM1 and CAV-1 could enhance the inhibitory effect of CAV-1 on ERK activation.