Role of UBE4B in the Ubiquitination of the HTLV-1 Tax Oncoprotein and NF-kappaB Activation

[摘要] Human T-cell leukemia virus type 1 (HTLV-1) is the etiological agent of adult T-cell leukemia and lymphoma (ATLL), an aggressive CD4+CD25+ malignancy. The HTLV-1 genome encodes the Tax protein that plays essential regulatory roles in oncogenic transformation of T lymphocytes by deregulating different cellular pathways, most notably NF-κB. Lysine 63 (K63)-linked polyubiquitination of Tax provides an important regulatory mechanism that promotes Tax-mediated interaction with the IKK complex and activation of NF-κB. However, the E3 ligase(s) and other host proteins regulating Tax ubiquitination are currently unknown. To identify novel Tax interacting proteins that may regulate its ubiquitination we conducted a yeast two-hybrid screen using Tax as bait. This screen yielded the E3/E4 ligase ubiquitin conjugation E4 B (UBE4B) as a novel binding partner for Tax. Here, we confirmed the interaction between Tax and UBE4B in mammalian cells by co-immunoprecipitation assays and demonstrated that they co-localized in the cytoplasm by confocal microscopy. Overexpression of UBE4B specifically enhanced Tax-induced NF-κB activation, whereas knockdown of UBE4B impaired Tax-induced NF-κB activation and induction of NF-κB target genes in Jurkat T cells and ATL cell lines. Although the UBE4B promoter contains putative NF-κB binding sites, its expression was not upregulated by Tax. Furthermore, depletion of UBE4B with shRNA promoted apoptotic cell death and diminished the proliferation of ATL cell lines. Finally, overexpression of UBE4B enhanced Tax polyubiquitination and knockdown of UBE4B suppressed the K63-linked polyubiquitination of Tax. Collectively, these results implicate UBE4B in Tax-induced NF-κB activation, cell survival and Tax K63-linked polyubiquitination.

[发布机构] Johns Hopkins University

[效力级别] Tax

[关键词] HTLV-1;Tax;NF-κB;UBE4B;Immunology