title: Ubiquitin-associated (UBA) domain in human Fas associated factor 1 inhibits tumor formation by promoting Hsp70 degradation.
abstract: Human Fas associated factor 1 (hFAF1) is a pro-apoptotic scaffolding protein containing ubiquitin-associating (UBA), ubiquitin like 1 and 2 (UBL1, UBL2), and ubiquitin regulatory X (UBX) domains. hFAF1 interacts with polyubiquitinated proteins via its N-terminal UBA domain and with valosin containing protein (VCP) via its C-terminal UBX domain. Overexpression of hFAF1 or its N-terminal UBA domain significantly increases cell death by increasing the degradation of polyubiquitinated proteins. In this study, we investigated whether hFAF1, whose expression level is reduced in cervical cancer, plays a role in tumor formation. We found that HeLa cells overexpressing full-length hFAF1 or the hFAF1 UBA domain alone, significantly suppressed the anchorage independent tumor growth in soft agar colony formation, increased cell death, and activated JNK and caspase 3. Employing UBA-specific tandem immunoprecipitation, we identified moieties specifically interacting with UBA domain of hFAF1, and found that polyubiquitinated Hsp70s are recruited to UBA domain. We also demonstrated that hFAF1 overexpression promotes Hsp70 degradation via the proteasome. We further found that mutating the UBA domain (I41N), as well as knocking down hFAF1 with specific RNAi, abolishs its ability to increase the proteasomal degradation of Hsp70. These findings suggest that hFAF1 inhibits tumor formation by increasing the degradation of Hsp70 mediated via its UBA domain.
authors.affiliation: Division of Life and Pharmaceutical Sciences, Department of Bioinspired Science, Drug Discovery Research, College of Pharmacy, Center for Cell Signaling, Ewha Womans University, Seoul, Korea.
authors.forename: Jae-Jin
authors.initials: JJ
authors.lastname: Lee
authors.forename: Young Mee
authors.initials: YM
authors.lastname: Kim
authors.forename: Jaeho
authors.initials: J
authors.lastname: Jeong
authors.forename: Duk Soo
authors.initials: DS
authors.lastname: Bae
authors.forename: Kong-Joo
authors.initials: KJ
authors.lastname: Lee
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051017:Apoptosis Regulatory Proteins; D016923:Cell Death / Q000235:genetics; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D015870:Gene Expression; D020868:Gene Silencing; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs / Q000235:genetics; D059748:Proteolysis; D054875:Ubiquitination
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C490780:FAF1 protein, human; D018840:HSP70 Heat-Shock Proteins; D047908:Intracellular Signaling Peptides and Proteins