Coronin 7, the mammalian POD-1 homologue, localizes to the Golgi apparatus

Coronins constitute an evolutionary conserved family of WD-repeat actin-binding proteins. Their primary function is thought to be regulating the actin cytoskeleton. Apart from that, several coronins were indirectly shown to participate in vesicular transport, establishment of cell polarity and cytokinesis. Here, we report a novel mammalian protein, coronin 7 (crn7), which is significantly different from other mammalian coronins in its domain architecture. Crn7 possesses two stretches of WD repeats in contrast to the other coronins only having one. The protein is expressed throughout the mouse embryogenesis and is strongly upregulated in brain and developing structures of the immune system in the course of development. In adult animals, both crn7 mRNA and protein are abundantly present in most organs, with significantly higher amounts in brain, kidney, thymus and spleen and lower amounts in muscle. At the subcellular level, the bulk of the protein appears to be present in the cytosol and in large cytosolic complexes. However, a significant portion of the protein is detected on vesicle-like cytoplasmic structures as well as on the cis-Golgi. In the Golgi region, crn7 staining appears broader than that of the cis-Golgi markers Erd2p and beta-COP, still, the trans-Golgi network appears predominantly crn7-negative. Importantly, the membrane-associated form of crn7 protein is phosphorylated on tyrosine residues, whereas the cytosolic form is not. Crn7 is the first coronin protein proven to localize to the Golgi membrane. We conclude that it plays a role in the organization of intracellular membrane compartments and vesicular trafficking rather than in remodeling the cytoskeleton.