Title
AAA chaperones related to posttranslational modifications, sumoylation and ubiquitylation

Akinobu Onitake & Yuki Murayama
Department of Molecular Cell Biology, IMEG, Kumamoto University

1.Caenorhabditis elegans  fidgetin homolog FIGL-1, a nuclear-localized AAA ATPase, binds to SUMO

Akinobu Onitake

Abstract: Fidgetin is a member of the AAA (ATPases associated with diverse cellular activities) chaperones. It is well-known that the specific function of a given AAA protein primarily depends upon its subcellular localization and interacting partners. FIGL-1, a  Caenorhabditis elegans  homolog of mammalian fidgetin, is localized in the nucleus. Here, we identified that the N-terminal PKRVK sequence of FIGL-1 functions as a monopartite nuclear localization signal. Nuclear localization of FIGL-1 is required for its function. We also found that FIGL-1 specifically interacted with SMO-1, a  C. elegans homolog of small ubiquitin-like modifier (SUMO), using a yeast two-hybrid assay. Furthermore, the direct physical interaction between FIGL-1 and SMO-1 was demonstrated by pull-down assay using purified proteins as well as immunoprecipitation assay using lysates from epitope-tagged SMO-1-expressing worms. Binding of FIGL-1 to SMO-1 is required for its function. The depletion of FIGL-1 and SMO-1 resulted in developmental defects in  C. elegans  . Taken altogether, our results indicate that FIGL-1 is a nuclear protein and that in concert with SMO-1, FIGL-1 plays an important role in the regulation of  C. elegans  development.

2.Characterization of cellular functions of UFD-2 and UFD-3, C-terminal adaptors for CDC-48, inC. elegans .

Yuki Murayama

Abstract: CDC-48 is a member of the AAA protein family, and is proposed to serve as a molecular chaperone in the ubiquitin signaling pathway. CDC-48 participates in a wide range of cellular activities, including organelle membrane fusion, protein degradation, transcriptional activation, cell-cycle control, apoptosis, and DNA repair. The functional diversity of CDC-48 is determined by differential interactions with a variety of cofactors and adaptors. Several adaptors have been identified in C. elegans , e.g. NPL-4-UFD-1 and UBXN proteins, which bind to the N-terminal domain of CDC-48, and UFD-2 and UFD-3, which bind to the C-terminal portion of CDC-48. However, their cellular functions have not yet been elucidated, especially in multicellular organisms. To clarify cellular functions of the C-terminal adaptors UFD-2 and UFD-3, we analyzed deletion mutants of ufd-2 and ufd-3 of C. elegans in terms of sex determination, ER stress response and meiotic chromosome segregation. Brood size of the ufd-3 mutant dramatically decreased, while that of the ufd-2 mutant was similar to that of wild type. The ufd-2 mutation significantly suppressed the reduced brood size of ufd-3 . On the other hand, the ufd-2 mutant was more sensitive to an ER-stress inducible reagent, tunicamycin, while the ufd-3 mutant and the ufd-2; ufd-3 double mutant showed hyper-resistance to it. These results suggest that UFD-2 and UFD-3 functions in an antagonistic manner. We will discuss the functional diversity of CDC-48 through differential binding of UFD-2 and UFD-3 adaptors.