Polyubiquitin chain-dependent protein degradation in TRIM30 cytoplasmic bodies

Viral infection induces numerous tripartite motif (TRIM) proteins to control antiviral immune signaling and viral replication. Particularly, SPRY-containing TRIM proteins are found only in vertebrates and they control target protein degradation by their RING-finger and SPRY domains, and proper cytoplasmic localization. To understand TRIM30 function, we analyzed its localization pattern and putative roles of its RING-finger and SPRY domains. We found that TRIM30 is located in actin-mediated cytoplasmic bodies and produces colocalized ubiquitin chains in SPRY domain- and RING-finger domain-dependent ways that are degraded by autophagy and the proteasome. These results suggest a TRIM protein-dependent degradation mechanism by cytoplasmic body formation with actin networks. Immunity: Viral defenses and the cell skeleton A protein involved in antiviral responses forms clusters in mouse cells known as cytoplasmic bodies that help break down viral proteins. Young-Joon Kim and colleagues from Yonsei University in Seoul, South Korea, used fluorescent markers to analyze the subcellular localization pattern of tripartite motif (TRIM)30, a mouse protein that aids in host defenses against viral infections. TRIM30 is a close relative of the human protein TRIM5 that is known to target the coat protein of incoming retroviruses and inhibit their replication. The researchers also examined the functions of each structural region of TRIM30. They observed that the assembly of TRIM30 into cytoplasmic bodies required a particular region of the protein, called SPRY, to interact with the filaments of the cell's internal skeleton. This interaction is essential for the antiviral function of TRIM30.