The ubiquitin ligase HERC4 mediates c-Maf ubiquitination and delays the growth of multiple myeloma xenografts in nude mice

Abstract

Key Points• HERC4 is the first identified ubiquitin ligase that mediates c-Maf ubiquitination and degradation.• HERC4 suppresses MM cell proliferation and delays MM tumor growth.The transcription factor c-Maf is extensively involved in the pathophysiology of multiple myeloma (MM), a fatal malignancy of plasma cells. In the present study, affinity chromatography and mass spectrometry were used to identify c-Maf ubiquitination-associated proteins, from which the E3 ligase HERC4 was found to interact with c-Maf and catalyzed its polyubiquitination and subsequent proteasome-mediated degradation. HERC4 mediated polyubiquitination at K85 and K297 in c-Maf, and this polyubiquitination could be prevented by the isopeptidase USP5. Further analysis on the NCI-60 cell line collection revealed that RPMI 8226, a MM-derived cell line, expressed the lowest level of HERC4. Primary bone marrow analysis revealed HERC4 expression was high in normal bone marrow, but was steadily decreased during myelomagenesis. These findings suggested HERC4 played an important role in MM progression. Moreover, ectopic HERC4 expression decreased MM proliferation in vitro, and delayed xenograft tumor growth in vivo. Therefore, modulation of c-Maf ubiquitination by targeting HERC4 may represent a new therapeutic modality for MM. (Blood. 2016;127(13):1676-1686

The transmembrane protein TMEPAI induces myeloma cell apoptosis by promoting degradation of the c-Maf transcription factor

“…Multiple myeloma (MM) is an incurable hematological malignancy derived from plasma cells, and it is the second highest blood cancer and accounts for 2% overall cancer cases. MM is featured with chromosomal translocations which lead to overexpression of several key genes, including the transcription factor c-Maf (13,14) which promotes MM cell proliferation and development (15,16). In the present study, we found that TMEPAI induces the ubiquitination and degradation of c-Maf and induces MM cell apoptosis independent of TGF-β signaling.…”

“…Our previous studies have showed that ubiquitin ligase HERC4 and ubiquitin-conjugating enzyme UBE2O lead to c-Maf degradation (13,18). To find out whether there were any other enzymes that might mediate c-Maf degradation, a small collection of plasmids (The Hopsital for Sick Children, Toronto, Canada) that were involved in proteolysis was screened.…”

“…The Antibodies against GAPDH, HA, Myc and Flag were purchased from MBL (Tokyo, Japan). The c-Maf, MafA and MafB plasmids were prepared as described previously (13). The TMEPAI gene was cloned from A549 cells and then subcloned into a pcDNA3.1 vector with a Flag or a Myc tag.…”

“…Informed consent was obtained in accordance with the Declaration of Helsinki. Mono-nuclear cells were isolated by Lympholyte® Cell Separation (Cedarlane, Canada) as described previously (13).…”

HERC4 Is Overexpressed in Hepatocellular Carcinoma and Contributes to the Proliferation and Migration of Hepatocellular Carcinoma Cells

“…Previous works have shown that HERC4 contributes to the occurrence and development of cancer. HERC4 plays an important role in myeloma (Zhang et al, 2016). In addition, some investigators verified that HERC4 highly expresses in lung cancer and breast cancer (Zhou et al, 2013;Zeng et al, 2015).…”