PPPDE1 promotes hepatocellular carcinoma development by negatively regulate p53 and apoptosis.

We have previously identified that PPPDE1 is a deubiquitinase (DUB) belonging to a cysteine isopeptidase family. Here we sought to explore the biological significance of PPPDE1 in hepatocellular carcinoma and its underlying molecular mechanism. In the present study, we found that amplification and overexpression of PPPDE1 were associated with poor prognosis in hepatocellular carcinoma (HCC). We also demonstrated that knocking down of PPPDE1 could significantly block the clonal growth and tumorigenicity of human HCC cells, which revealed a critical role for PPPDE1 in HCC development. Furthermore, we proved that PPPDE1 is a key modulator of p53 protein level and its down stream apoptosis pathway. Taken together, these results suggested that PPPDE1 is a putative HCC driver gene and extensive studies should be conducted in the future to investigate the role of PPPDE1 in HCC and other tumors.

Identification of USP18 as an important regulator of the susceptibility to IFN-alpha and drug-induced apoptosis.

Gene products that modify the apoptotic susceptibility of cancer cells may offer novel drug response markers or therapeutic targets. In this study, we probed the contribution of 53 different isopeptidases to apoptosis triggered by bortezomib and etoposide. USP18, a type I IFN-induced protein that deconjugates the ubiquitin-like modifier ISG15 from target proteins, was found to limit apoptotic susceptibility to IFN-alpha or bortezomib. Ablating USP18 in cells treated with IFN-alpha increased tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) production; upregulated expression of transcription factors IFN-regulatory factor (IRF)-1, IRF-7, and IRF-9; and promoted the extrinsic pathway of apoptosis. The proapoptotic effects of ablating USP18 were abrogated by FLIP overexpression or TRAIL silencing. However, in bortezomib-treated cells, weak spontaneous signaling from type I IFNs was implicated in the proapoptotic effect of USP18 ablation. Ectopic USP18 repressed apoptotic signaling by IFN-alpha, TRAIL, or bortezomib. Similar effects were produced by a catalytically inactive USP18 mutant, indicating that the antiapoptotic function of USP18 is independent of its catalytic activity. These findings suggest that USP18 may significantly limit operation of the extrinsic apoptotic pathway triggered by type I IFN and drugs.

CSN5 isopeptidase activity links COP9 signalosome activation to breast cancer progression.

CSN5 has been implicated as a candidate oncogene in human breast cancers by genetic linkage with activation of the poor-prognosis, wound response gene expression signature. CSN5 is a subunit of the eight-protein COP9 signalosome, a signaling complex with multiple biochemical activities; the mechanism of CSN5 action in cancer development remains poorly understood. Here, we show that CSN5 isopeptidase activity is essential for breast epithelial transformation and progression. Amplification of CSN5 is required for transformation of primary human breast epithelial cells by defined oncogenes. The transforming effects of CSN5 require CSN subunits for assembly of the full COP9 signalosome and the isopeptidase activity of CSN5, which potentiates the transcriptional activity of MYC. Transgenic inhibition of CSN5 isopeptidase activity blocks breast cancer progression evoked by MYC and RAS in vivo. These results highlight CSN5 isopeptidase activity in breast cancer progression, suggesting it as a therapeutic target in aggressive human breast cancers.

Biodegradation of all stereoisomers of the EDTA substitute iminodisuccinate by Agrobacterium tumefaciens BY6 requires an epimerase and a stereoselective C-N lyase.

Biodegradation tests according to Organization for Economic Cooperation and Development standard 301F (manometric respirometry test) with technical iminodisuccinate (IDS) revealed ready biodegradability for all stereoisomers of IDS. The IDS-degrading strain Agrobacterium tumefaciens BY6 was isolated from activated sludge. The strain was able to grow on each IDS isomer as well as on Fe(2+)-, Mg(2+)-, and Ca(2+)-IDS complexes as the sole carbon, nitrogen, and energy source. In contrast, biodegradation of and growth on Mn(2+)-IDS were rather scant and very slow on Cu(2+)-IDS. Growth and turnover experiments with A. tumefaciens BY6 indicated that the isomer R,S-IDS is the preferred substrate. The IDS-degrading enzyme system isolated from this organism consists of an IDS-epimerase and a C-N lyase. The C-N lyase is stereospecific for the cleavage of R,S-IDS, generating d-aspartic acid and fumaric acid. The decisive enzyme for S,S-IDS and R,R-IDS degradation is the epimerase. It transforms S,S-IDS and R,R-IDS into R,S-IDS. Both enzymes do not require any cofactors. The two enzymes were purified and characterized, and the N-termini were sequenced. The purified lyase and also the epimerase catalyzed the transformation of alkaline earth metal-IDS complexes, while heavy metal-IDS complexes were transformed rather slowly or not at all. The observed mechanism for the complete mineralization of all IDS isomers involving an epimerase offers an interesting possibility of funneling all stereoisomers into a catabolic pathway initiated by a stereoselective lyase.