HERC3 binding to and regulation by ubiquitin

Abstract

Members of the HERC (domain homologous to E6 associated protein carboxy-terminus and RCC1 domain protein) family may function both as guanine nucleotide exchange factors and E3 ubiquitin ligases. Here we identify an unstudied member, HERC3. This protein was recognized by specific antibodies in different cell types. HERC3 was located in the cytosol and in vesicular-like structures containing L L-COP, ARF and Rab5 proteins. Involvement of HERC3 in the ubiquitin system was suggested by its ability to interact with ubiquitin. The conserved cysteine in HECT proteins was not essential for this non-covalent binding. Moreover, HERC3 was a substrate of ubiquitination being degraded by the proteasome. These observations indicate a fine regulation of HERC3 and suggest a role in vesicular traffic and ubiquitin-dependent processes. ß

HERC5, a HECT E3 ubiquitin ligase tightly regulated in LPS activated endothelial cells

“…The protein belongs to the HERC family as it contains both a HECT (homologous to E6-AP C-terminus) domain necessary for transfer of ubiquitin and RCC1 (regulator of chromosome condensation) repeats with putative GTP exchange activity and is termed HERC5 (Cruz et al, 2001). The cDNA obtained by us is similar to the Ceb1 cDNA identified in a yeast two-hybrid screen for cyclin-E-binding proteins (Mitsui et al, 1999) and both represent HERC5.…”

“…HERC1 and HERC2 are closely related, giant proteins of more than 500 kDa and are both suggested to play a role in vesicular trafficking (Lehman et al, 1998;Rosa and Barbacid, 1997;Rosa et al, 1996). HERC3 is a ubiquitously expressed gene and the encoded protein is located both in the cytosol and in vesicular-like structures (Cruz et al, 2001). Although all HERC family members contain a HECT domain, ubiquitin Journal of Cell Science 117 (20) ligase activity was hitherto shown only for HERC3 (Cruz et al, 2001;Huibregtse et al, 1995).…”

“…HERC3 is a ubiquitously expressed gene and the encoded protein is located both in the cytosol and in vesicular-like structures (Cruz et al, 2001). Although all HERC family members contain a HECT domain, ubiquitin Journal of Cell Science 117 (20) ligase activity was hitherto shown only for HERC3 (Cruz et al, 2001;Huibregtse et al, 1995). The E2 enzymes UbcH5a and UbcH7 have been reported to transfer ubiquitin to HECT domain proteins; in fact, UbcH7 is used by HERC3 (Schwarz et al, 1998).…”

“…With respect to the putative guanine exchange factor (GEF) activity of the RCC1 repeats in HERCs, GEF activity was shown only for HERC1 on ARF1, Rab3A and Rab5, consistent with its vesicular localization (Rosa et al, 1996). For HERC3 such a function was not detectable (Cruz et al, 2001). HERC5 does not localize to cytosolic vesicles (Mitsui et al, 1999) (data not shown) and therefore, a role as GEF for Rab and Rho GTPases is unlikely.…”

Positive Regulation of Interferon Regulatory Factor 3 Activation by Herc5 via ISG15 Modification

“…HERC proteins are suggested to have E3 ligase activity. In particular, HERC3 has been shown to be a ubiquitin binding protein (5). The expression of HERC5 is especially high in testis and fetal brain but low in most tissues (22).…”