ULK2 Export from Nuclear by CRM1 Enhances its Autophagy Activity

Author(s): Kiwol Kim, Eun Jeoung Lee, Otgonnamjil Davaadorj, Do Won Kyoung Park, Sung Hwa Shin, Sunghee Hyun, Sang Sun Kang

Uncoordinated 51-like kinase 2 (ULK2) which plays an essential role in the regulation of autophagy in mammalian cells is a member of the serine/threonine kinase family. Because of the role of autophagy in normal cellular homeostasis and multiple diseases, better mechanistic insights into this process may result in the development of novel therapeutic approaches. Previously, we reported a potential NES motif in the N-terminal domain of ULK2, which is required to import into the nuclear. Here, we present evidence that ULK2 associates with chromosome region maintenance 1(CRM1) for its export from the nucleus, reversely. The potential NES motif (³⁸iksinkknlsksqill⁵³) in the protein kinase domain of ULK2 is noticed; this motif is similar to the consensus NES motif (Φx_2-3Φx_2-3LxL/I). Using a pull-down approach, we observed that ULK2 interacts physically with CRM1 both in vivo and in vitro. Confocal microscopy confirmed the co-localization of ULK2 and CRM1. Localization of ULK2 to the nuclear region was disrupted by mutations in the putative CRM1-binding motif (³⁸iksinkknlsksqill⁵³→³⁸iksinkknlsksqDll⁵³; I51D). Furthermore, in transient transfection assays, absence of the CRM1 binding site mutant (nuclear localization form) was associated with a substantial decrease in autophagy activity (but decrease in the in vitro serine-phosphorylation) compared with ULK2 wild type. Thus, we suggest that CRM1 interacts with ULK2 through ULK2’s putative NES motif and exports it from the nucleus to the cytoplasm thereby playing a role as a shuttle protein.