Triad3A, an E3 Ubiquitin-protein Ligase Regulating Toll-like Receptors

Activation of Toll-like receptors (TLRs) results in a proinflammatory response needed to combat infection. Thus, limiting TLR signaling is essential for preventing a protective response from causing injury to the host. Here we describe how a RING finger protein, Triad3A, acts as an E3 ubiquitin-protein ligase and enhances ubiquitination and proteolytic degradation of some TLRs. Triad3A overexpression promoted substantial degradation of TLR4 and TLR9 with a concomitant decrease in signaling, but did not affect TLR2 expression or signaling. Conversely, a reduction in endogenous Triad3A by small interfering RNA increased TLR expression and enhanced TLR activation. Thus, ubiquitination by Triad3A represents one pathway by which the intensity and duration of TLR signaling is controlled.