Article

Herc5, an interferon-induced HECT E3 enzyme, is required for conjugation of ISG15 in human cells

Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, Texas, United States
Journal of Biological Chemistry (Impact Factor: 4.57). 03/2006; 281(7):4334-8. DOI: 10.1074/jbc.M512830200
Source: PubMed

ABSTRACT ISG15 is an interferon (IFN)-alpha/beta-induced ubiquitin-like protein that is conjugated to cellular proteins during innate immune responses to viral and bacterial infections. A recent proteomics study identified 158 human proteins targeted for ISG15 conjugation, including the ISG15 E1 and E2 enzymes (Ube1L and UbcH8, respectively) and a HECT E3 enzyme, Herc5. Like the genes encoding Ube1L and UbcH8, expression of Herc5 was also induced by IFN-beta, suggesting that Herc5 might be a component of the ISG15 conjugation system. Consistent with this, small interfering RNAs targeting Herc5 had a dramatic effect on overall ISG15 conjugation in human cells, abrogating conjugation to the vast majority of ISG15 target proteins in vivo. In addition, co-transfection of plasmids expressing ISG15, Ube1L, UbcH8, and Herc5 resulted in robust ISG15 conjugation in non-IFN-treated cells, while the active-site cysteine mutant of Herc5 or a mutant lacking the RCC1 repeat region did not support ISG15 conjugation. These results demonstrate that Herc5 is required for conjugation of ISG15 to a broad spectrum of target proteins in human cells.

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    • "HERC5 is ubiquitously expressed in many cell types and tissues including, but not limited to, effector and central memory T cells, dendritic cells, CD14+ monocytes, monocyte-derived macrophages, embryonic and induced pluripotent stem cells, hematopoietic and granulopoietic stem cells, testis (germ and leydig cells), ovary, liver and lung [5-17]. HERC5 expression is up-regulated in response to IFN [18,19], in vitro and in vivo virus infection [1,20-25], lipopolysaccharide, tumor necrosis factor α, and interleukin-1β [26]. "
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    • "They are characterized by having a C-terminal HECT domain, involved in both accepting ubiquitin from an ubiquitin-conjugating protein and catalyzing its transfer to the protein to be ubiquitinated [16]. It has been also shown that a few mammalian HECT proteins may attach the ubiquitin-like protein ISG15, instead of ubiquitin, to its substrates [17]–[19]. The functions of animal HECTs have been studied in detail. "
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