title: Degradation of activated K-Ras orthologue via K-Ras-specific lysine residues is required for cytokinesis.
abstract: Mammalian cells encode three closely related Ras proteins, H-Ras, N-Ras, and K-Ras. Oncogenic K-Ras mutations frequently occur in human cancers, which lead to dysregulated cell proliferation and genomic instability. However, mechanistic role of the Ras isoform regulation have remained largely unknown. Furthermore, the dynamics and function of negative regulation of GTP-loaded K-Ras have not been fully investigated. Here, we demonstrate RasG, the Dictyostelium orthologue of K-Ras, is targeted for degradation by polyubiquitination. Both ubiquitination and degradation of RasG were strictly associated with RasG activity. High resolution tandem mass spectrometry (LC-MS/MS) analysis indicated that RasG ubiquitination occurs at C-terminal lysines equivalent to lysines found in human K-Ras but not in H-Ras and N-Ras homologues. Substitution of these lysine residues with arginines (4KR-RasG) diminished RasG ubiquitination and increased RasG protein stability. Cells expressing 4KR-RasG failed to undergo proper cytokinesis and resulted in multinucleated cells. Ectopically expressed human K-Ras undergoes polyubiquitin-mediated degradation in Dictyostelium, whereas human H-Ras and a Dictyostelium H-Ras homologue (RasC) are refractory to ubiquitination. Our results indicate the existence of GTP-loaded K-Ras orthologue-specific degradation system in Dictyostelium, and further identification of the responsible E3-ligase may provide a novel therapeutic approach against K-Ras-mutated cancers.
authors: From the Division of Hematology Oncology, Department of Internal Medicine, University of Cincinnati Cancer Institute, Department of Neurosurgery, University of Cincinnati Neuroscience Institute, Brain Tumor Center University of Cincinnati, College of Medicine, Cincinnati, Ohio 45267.
authors: Kazutaka
authors: K
authors: Sumita
authors: Hirofumi
authors: H
authors: Yoshino
authors: Mika
authors: M
authors: Sasaki
authors: Nazanin
authors: N
authors: Majd
authors: Emily Rose
authors: ER
authors: Kahoud
authors: Hidenori
authors: H
authors: Takahashi
authors: Koh
authors: K
authors: Takeuchi
authors: Taruho
authors: T
authors: Kuroda
authors: Susan
authors: S
authors: Lee
authors: Pascale G
authors: PG
authors: Charest
authors: Kosuke
authors: K
authors: Takeda
authors: John M
authors: JM
authors: Asara
authors: Richard A
authors: RA
authors: Firtel
authors: Dimitrios
authors: D
authors: Anastasiou
authors: Atsuo T
authors: AT
authors: Sasaki
mesh_terms: D048749:Cytokinesis / Q000502:physiology*; D004023:Dictyostelium / Q000201:enzymology* / Q000235:genetics; D006160:Guanosine Triphosphate / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008239:Lysine / Q000235:genetics / Q000378:metabolism; D055550:Protein Stability; D059748:Proteolysis; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras); D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination / Q000502:physiology*; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D015800:Protozoan Proteins; C424065:rasG protein, Dictyostelium; D006160:Guanosine Triphosphate; D044767:Ubiquitin-Protein Ligases; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins; D008239:Lysine
keywords: Cancer Biology; Cytokinesis; Dictyostelium; Molecular Cell Biology; Ras; Signaling; Ubiquitination