Human Trim5α has additional activities that are uncoupled from retroviral capsid recognition.

Trim5α is a host antiviral protein that recognizes incoming retroviral capsids in the cytoplasm and prevents productive infections. Although present in most mammals, the state of the Trim5 gene is dynamic in that primates have one copy with several splice variants, while rodents and cows have multiple copies. Mouse Trim30 (one of the mouse Trim5α homologs) has been shown to negatively regulate NF-kappaB activation by targeting upstream signaling intermediates TAB2 and TAB3 for degradation. We show that human Trim5α also affects levels of TAB2, resulting in abrogation of TAB2-dependent NF-kappaB activation. Surprisingly, unlike mouse Trim30, human and rhesus Trim5α are able to activate NF-kappaB-driven reporter gene expression in a dose-dependent manner. We show that Trim5α uses distinct domains for the distinct abilities of affecting TAB2 levels, regulating NF-kappaB, and recognizing retroviral capsids. Our results demonstrate functions of Trim5α that are not dependent on recognizing the retroviral capsid.