Ubiquitin-mediated proteasomal degradation in normal and malignant hematopoiesis

SF3B4 Depletion Retards the Growth of A549 Non-Small Cell Lung Cancer Cells via UBE4B-Mediated Regulation of p53/p21 and p27 Expression

Splicing factor B subunit 4 (SF3B4), a component of the U2-pre-mRNA spliceosomal complex, contributes to tumorigenesis in several types of tumors. However, the oncogenic potential of SF3B4 in lung cancer has not yet been determined. The in vivo expression profiles of SF3B4 in non-small cell lung cancer (NSCLC) from publicly available data revealed a significant increase in SF3B4 expression in tumor tissues compared to that in normal tissues. The impact of SF3B4 deletion on the growth of NSCLC cells was determined using a siRNA strategy in A549 lung adenocarcinoma cells. SF3B4 silencing resulted in marked retardation of the A549 cell proliferation, accompanied by the accumulation of cells at the G0/G1 phase and increased expression of p27, p21, and p53. Double knockdown of SF3B4 and p53 resulted in the restoration of p21 expression and partial recovery of cell proliferation, indicating that the p53/p21 axis is involved, at least in part, in the SF3B4-mediated regulation of A549 cell proliferation. We also provided ubiquitination factor E4B (UBE4B) is essential for p53 accumulation after SF3B4 depletion based on followings. First, co-immunoprecipitation showed that SF3B4 interacts with UBE4B. Furthermore, UBE4B levels were decreased by SF3B4 depletion. UBE4B depletion, in turn, reproduced the outcome of SF3B4 depletion, including reduction of polyubiquitinated p53 levels, subsequent induction of p53/p21 and p27, and proliferation retardation. Collectively, our findings indicate the important role of SF3B4 in the regulation of A549 cell proliferation through the UBE4B/p53/p21 axis and p27, implicating the therapeutic strategies for NSCLC targeting SF3B4 and UBE4B.

Differential Degradation of TRA2A and PYCR2 Mediated by Ubiquitin E3 Ligase E4B

E4B belongs to the U-box E3 ligase family and functions as either an E3 or an E4 enzyme in protein ubiquitination. Transformer2A (TRA2A) and Pyrroline-5-carboxylate reductase 2 (PYCR2) are related to cancer development and are overexpressed in many cancer cells. The degradation of TRA2A and PYCR2 mediated by the ubiquitin-proteasome system (UPS) has not been reported. This study validated that E4B could ubiquitinate TRA2A and PYCR2 as an E3 ligase both in vitro and in the HEK293 cells. E4B mediated the degradation by forming K11- and K48- linked polyubiquitin chains on TRA2A and PYCR2, respectively. E4B regulated the alternative splicing function of TRA2A and affected RSRC2 transcription in the HEK293 cells. Although E4B is highly expressed, it hardly degrades TRA2A and PYCR2 in hepatocellular carcinoma (HCC) cells, suggesting other mechanisms exist for degradation of TRA2A and PYCR2 in the HCC cells. We finally reported that E4B interacted with substrates via its variable region.

RNF34 ablation promotes cerebrovascular remodeling and hypertension by increasing NADPH-derived ROS generation

Cerebrovascular remodeling is the most common cause of hypertension and stroke. Ubiquitin E3 ligase RING finger protein 34 (RNF34) is suggested to be associated with the development of multiple neurological diseases. However, the importance of RNF34 in cerebrovascular remodeling and hypertension is poorly understood. Herein, we used mice with a global RNF34 knockout as well as RNF34 floxed mice to delete RNF34 in endothelial cells and smooth muscle cells (SMCs). Our results showed that global RNF34 knockout mice substantially promoted angiotensin II (AngII)-induced middle cerebral artery (MCA) remodeling, hypertension, and neurological dysfunction. Endothelial cell RNF34 did not regulate the development of hypertension. Rather, SMC RNF34 expression is a critical regulator of hypertension and MCA remodeling. Loss of RNF34 enhanced AngII-induced mouse brain vascular SMCs (MBVSMCs) proliferation, migration and invasion. Furthermore, MCA and MBVSMCs from SMC RNF34-deficient mice showed increased superoxide anion and reactive oxygen species (ROS) generation as well as nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, but exhibited no marked effect on mitochondria-derived ROS. Knockout of RNF34 promoted p22^phox expression, leading to increased binding of p22^phox/p47^phox and p22^phox/NOX2, and eventually NADPH oxidase complex formation. Immunoprecipitation assay identified that RNF34 interacted with p22^phox. RNF34 deletion increased p22^phox protein stability by inhibiting ubiquitin-mediated degradation. Blockade of NADPH oxidase activity or knockdown of p22phox significantly abolished the effects of RNF34 deletion on cerebrovascular remodeling and hypertension. Collectively, our study demonstrates that SMC RNF34 deficiency promotes cerebrovascular SMC hyperplasia and remodeling by increased NADPH-derived ROS generation via reducing p22^phox ubiquitin-dependent degradation.

The Roles of Ubiquitination Factor E4B (UBE4B) in the Postoperative Prognosis of Patients with Renal Cell Carcinoma and in Renal Tumor Cells Growth and Metastasis

Object

This study aimed at investigating the clinical significance and biological function of ubiquitination factor E4B (UBE4B) in human renal cell carcinoma (RCC).

Methods

19 paired clear cell renal cell carcinoma (ccRCC) tumor samples and the matched neighboring non-tumor samples were used to detect the expression of UBE4B in RCC tumor by Western blotting and RT-qPCR. UBE4B expression was also detected in 151 ccRCC paraffin-embedded tumor samples by using immunohistochemistry. Overall survival (OS) in different UBE4B expression groups were compared with Log rank test. The prognostic value of UBE4B expression in OS was evaluated with the univariate and multivariate Cox regression models. UBE4B was knocked down by small interfering RNA (siRNA) technology, and the effect of UBE4B on cell proliferation, colony formation, metastasis, apoptosis and cell cycle of RCC cells were examined in vitro.

Results

Both protein and mRNA levels of UBE4B were up-regulated in ccRCC tumor tissues in contrast to the corresponding adjacent nontumor ones. UBE4B expression was positively associated with tumor-node-metastasis (TNM) stage and distant metastasis in ccRCC patients. Survival analyses indicated that low expression of UBE4B was associated with increased OS in ccRCC patients. Functional analyses demonstrated that siRNA silencing of UBE4B expression in SKRC39 and ACHN cells further reduced the growth, motility and invasiveness of RCC cells. Moreover, siRNA silencing of UBE4B in the RCC cell lines did not induce apoptosis, and an increase in the cell population was observed during the G₀/G₁ phase of the cell cycle.

Conclusion

UBE4B might act as an oncogene in regulating RCC development. Therefore it could be served as an effective indicator to predict OS and a potential biomarker for targeted therapy of RCC patients.

Silencing UBE4B induces nasopharyngeal carcinoma apoptosis through the activation of caspase3 and p53

Aim

The human ubiquitination factor E4B (UBE4B) gene is frequently amplified in some solid cancers. However, the role of UBE4B in nasopharyngeal carcinoma (NPC) has not yet been investigated.

Methods

Firstly, we analyzed the expression of UBE4B in NPC samples using real-time quantitative PCR and Western blot analysis. After knocking down UBE4B using small interfering RNA technology, the functions of UBE4B on cell proliferation, apoptosis, and cell cycle, as well as underlying mechanism, were investigated.

Results

Compared with matched adjacent non-tumor tissues, both protein and mRNA levels of UBE4B were much higher in most NPC cancerous specimens. Deficiency of UBE4B could significantly inhibit tumor cell growth and induce cell apoptosis. Knocking down UBE4B could promote the expression of cleaved caspase3 and p53, and inhibition of caspase3 could prevent cell apoptosis induced by the deficiency of UBE4B.

Conclusion

These results indicate that expression of UBE4B was higher in most NPC tissues compared to adjacent non-tumoral tissues, and that knockdown of UBE4B inhibited the cell growth and induced apoptosis in NPC cells. This process was regulated by the activation of caspase3 and p53. Thus, UBE4B gene might act as a potential molecular target to develop novel strategy for NPC patients.

E3 Ubiquitin ligase RNF183 Is a Novel Regulator in Inflammatory Bowel Disease

BACKGROUND AND AIMS

Specific members of the RING finger [RNF] protein family serve as E3 ubiquitin ligases and play important roles in the regulation of inflammation. However, their roles in the pathogenesis of inflammatory bowel disease [IBD] have not been explored.

METHODS

Genomic microarray of inflamed colon samples from Crohn's disease [CD] patients was performed to identify potential up-regulated genes. Expression of the identified highly up-regulated RNF183 gene was subsequently examined by quantitative reverse transcription polymerase chain reaction [qRT-PCR], western blotting and immunohistochemistry of the intestinal tissues of IBD patients and the colons of trinitrobenzene sulphonic acid [TNBS]-induced colitic mice. RNF183-mediated interaction with the NF-κB pathway and ubiquitination of IκBα were examined by siRNA, plasmid transfection, and immunoprecipitation. The miRNA predicted to target RNF183 was explored and its role in the RNF183/ NF-κB pathway was investigated.

RESULTS

RNF183 was up-regulated in intestinal epithelial cells in IBD patients and in colitic mice. RNF183 promoted intestinal inflammation via the activation of the NF-κB pathway by increasing the ubiquitination and degradation of IκBα. Computational analysis identified putative binding of miR-7 to RNF183. Transfection of intestinal cells with a miR-7 mimic or inhibitor confirmed its negative regulatory effect on RNF183 expression and ubiquitination of IκBα. miR-7 was down-regulated in inflamed colon tissues of IBD patients and colitic mice.

CONCLUSIONS

RNF183, which is negatively regulated by miR-7, is a novel regulator promoting intestinal inflammation by increasing the ubiquitination and degradation of IκBα, thereby inducing NF-κB activation. The interaction between RNF183-mediated ubiquitination and miRNA may be an important novel epigenetic mechanism in the pathogenesis of IBD.

NEDD4 Regulates PAX7 Levels Promoting Activation of the Differentiation Program in Skeletal Muscle Precursors

The transcription factor Pax7 regulates skeletal muscle stem cell (satellite cells) specification and maintenance through various mechanisms, including repressing the activity of the muscle regulatory factor MyoD. Hence, Pax7-to-MyoD protein ratios can determine maintenance of the committed-undifferentiated state or activation of the differentiation program. Pax7 expression decreases sharply in differentiating myoblasts but is maintained in cells (re)acquiring quiescence, yet the mechanisms regulating Pax7 levels based on differentiation status are not well understood. Here we show that Pax7 levels are directly regulated by the ubiquitin-ligase Nedd4. Our results indicate that Nedd4 is expressed in quiescent and activated satellite cells, that Nedd4 and Pax7 physically interact during early muscle differentiation-correlating with Pax7 ubiquitination and decline-and that Nedd4 loss of function prevented this effect. Furthermore, even transient nuclear accumulation of Nedd4 induced a drop in Pax7 levels and precocious muscle differentiation. Consequently, we propose that Nedd4 functions as a novel Pax7 regulator, which activity is temporally and spatially controlled to modulate the Pax7 protein levels and therefore satellite cell fate.

Expression and prognostic role of ubiquitination factor E4B in primary hepatocellular carcinoma

Ubiquitination factor E4B (UBE4B) has been speculated to have contradictory functions upon tumorigenesis as an oncogene or tumor suppressor in different types of cancers. We investigated the expression and prognostic role of UBE4B in primary hepatocellular carcinoma (HCC) using cell lines and 149 archived HCC samples. Correlation between the functions of UBE4B in HCC was also explored. We used human HCC cell lines (HepG2, Hep3B, SK-Hep1, Huh7, SMMC-7721, BEL-7402) and a normal hepatocyte cell line (LO2) along with HCC samples from patients who had undergone resection for HCC previously at our hospital. A battery of methods (real-time quantitative polymerase chain reaction; Western blotting; immunohistochjemical analyses; cell proliferation and colony formation assays; cell migration and cell invasion assays) were employed to assess various aspects of UBE4B.We found that UBE4B expression was upregulated aberrantly at mRNA and protein levels in human primary HCC tissues. Amplified expression of UBE4B was highly correlated with poor outcome. Silencing of UBE4B expression by siRNA inhibited the proliferation, colony formation, migration and invasion of HCC cells in vitro, and resulted in significant apoptosis that was associated with downregulation of expression of Bcl-2 and upregulation of expression of total p53, p-p53, Bax and Cleaved-Caspase3 in HCC cells. Our findings suggested that UBE4B might have an oncogenic role in human primary HCC, and that it could be used as a prognostic marker (as well as a potential molecular target) for the treatment of HCC.

RING finger proteins are involved in the progression of barrett esophagus to esophageal adenocarcinoma: a preliminary study

BACKGROUND/AIMS

To investigate the differential expression of RING finger (RNF) proteins in Barrett esophagus (BE) and esophageal adenocarcinoma (EAC).

METHODS

The differential expression of RNFs in normal esophagus (NE), BE, and EAC was screened using microarray assay. Real-time quantitative polymerase chain reaction (PCR), tissue micro-array assay, and Western blot analysis were independently performed to detect the mRNA and protein expression of screened RNFs.

RESULTS

The expression of nine RNFs in the BE or EAC was 2-fold higher than those in NE. Among these proteins, the RNF32 and RNF121 expression in BE was 20.3-fold and 16.4-fold higher, respectively, than that in NE, and the expression of RNF24, RNF130, RNF141, RNF139, RNF11, RNF14, and RNF159 was upregulated more than 2-fold compared with NE. The expression of nine RNFs was not only upregulated in the EAC but was also positively related to the RNF expression in BE. The PCR results also indicated increased expression of these RNFs in BE and EAC compared to NE. Furthermore, the mRNA expression of all RNFs, except for RNF141 in EAC, was dramatically higher than those in the BE. Similar results were also obtained from the Western blot analysis.

CONCLUSIONS

A total of nine RNFs play critical roles in the progression of BE to EAC.

Differential regulation of PML-RARα stability by the ubiquitin ligases SIAH1/SIAH2 and TRIAD1

The ubiquitin proteasome system plays an important role in normal and malignant hematopoiesis and relies on the concerted action of three enzyme families. The E2 ubiquitin conjugase UBCH8 (ubiquitin conjugating enzyme [human] 8) cooperates with the E3 ubiquitin ligases SIAH1 and SIAH2 (seven in absentia homolog 1/2) to mediate the proteasomal degradation of oncoproteins. One such protein is the leukemia fusion protein PML-RARα (promyelocytic leukemia-retinoic acid receptorα) that is associated with acute promyelocytic leukemia. A limited number of UBCH8 interaction partners that participate in the UBCH8-dependent depletion of cancer-relevant proteins are known. We report here that TRIAD1 (two RING fingers and DRIL [double RING finger linked] 1), an E3 ubiquitin ligase relevant for the clonogenic growth of myloid progenitors, binds UBCH8 as well as PML-RARα. Moreover, there is concurrent induction of TRIAD1 and UBCH8 upon combinatorial treatment of acute promyelocytic leukemia cells with the pro-apoptotic epigenetic modulator valproic acid and the differentiation inducing agent all-trans retinoic acid. However, in sharp contrast to SIAH1/SIAH2 and UBCH8, TRIAD1 binding to PML-RARα has no effect on its turnover. In summary, our data exclude TRIAD1 as crucial regulator of the leukemic determinant PML-RARα, but highlight the prominence of the UBCH8/SIAH axis in PML-RARα degradation.

Identification of copy number alterations by array comparative genomic hybridization in patients with late chronic or accelerated phase chronic myeloid leukemia treated with imatinib mesylate

The outcome of treating chronic myeloid leukemia (CML) with imatinib mesylate (IM) is inferior when therapy is commenced in late chronic or accelerated phase as compared to early chronic phase. This may be attributed to additional genomic alterations that accumulate during disease progression. We sought to identify such lesions in patients showing suboptimal response to IM by performing array-CGH analysis on 39 sequential samples from 15 CML patients. Seventy-four cumulative copy number alterations (CNAs) consisting of 35 losses and 39 gains were identified. Alterations flanking the ABL1 and BCR genes on chromosomes 9 and 22, respectively, were the most common identified lesions with 5 patients losing variable portions of 9q34.11 proximal to ABL1. Losses involving 1p36, 5q31, 17q25, Y and gains of 3q21, 8q24, 22q11, Xp11 were among other recurrent lesions identified. Aberrations were also observed in individual patients, involving regions containing known leukemia-associated genes; CDKN2A/2B, IKZF1, RB1, TLX1, AFF4. CML patients in late stages of their disease, harbor pre-existing and evolving sub-microscopic CNAs that may influence disease progression and IM response.

Protacs for treatment of cancer

Protein degradation is the cell's mechanism of eliminating misfolded or unwanted proteins. The pathway by which proteins are degraded occurs through the ubiquitin-proteasome system. Ubiquitin is a small 9-kD (kDa) protein that is attached to proteins. A minimum of four ubiquitins are required for proteins to be recognized by the degradation machinery, known as the 26S proteasome. Defects in ubiquitination have been identified in a number of diseases, including cancer, neurodegenerative diseases, and metabolic disorders. We sought to exploit the delicate balance between protein synthesis and degradation to treat cancer by designing a chimeric molecule, known as Protac (Proteolysis Targeting Chimeric molecule). Protacs are heterobifunctional nanomolecules that are approximately 10 nm in size and can recruit proteins that cause cancer to the ubiquitin-proteasome machinery for degradation. In this review, we discuss the development of this novel technology for the treatment of cancer.

Implications of endoplasmic reticulum stress, the unfolded protein response and apoptosis for molecular cancer therapy. Part II: targeting cell cycle events, caspases, NF-κB and the proteasome

BACKGROUND

Endoplasmic reticulum stress (ERS), the unfolded protein response (UPR) and apoptosis signal transduction pathways are fundamental to normal cellular homeostasis and survival, but are exploited by cancer cells to promote the cancer phenotype.

OBJECTIVE

Collateral activation of ERS and UPR role players impact on cell growth, cell cycle arrest or apoptosis, genomic stability, tumour initiation and progression, tumour aggressiveness and drug resistance. An understanding of these processes affords promising prospects for specific cancer drug targeting of the ERS, UPR and apoptotic pathways.

METHOD

This review (Part II of II) brings forward the latest developments relevant to the molecular connections among cell cycle regulators, caspases, NF-κB, and the proteasome with ERS and UPR signalling cascades, their functions in apoptosis induction, apoptosis resistance and oncogenesis, and how these relationships can be exploited for targeted cancer therapy.

CONCLUSION

Overall, ERS, the UPR and apoptosis signalling cascades (the molecular therapeutic targets) and the development of drugs that attack these targets signify a success story in cancer drug discovery, but a more reductionist approach is necessary to determine the precise molecular switches that turn on antiapoptotic and pro-apoptotic programmes.

The ubiquitin conjugating enzyme, UbcM2, engages in novel interactions with components of cullin-3 based E3 ligases

The class III ubiquitin conjugating enzymes (E2s) are distinguished from other E2s by the presence of unique N-terminal domains, and the utilization of importin-11 for transport into the nucleus in an activation dependent fashion. To begin determining the physiological roles of these enzymes, we carried out a yeast two-hybrid screen with the class III E2, UbcM2. This screen retrieved RCBTB1, a putative substrate adaptor for a cullin3 (CUL3) E3 ligase. We initially established through biochemical studies that RCBTB1 has the properties of a CUL3 substrate adaptor. Further analysis of the UbcM2-RCBTB1 complex led to the discovery and characterization of the following novel interactions: (i) UbcM2 binds an N-terminal domain of CUL3 requiring the first 57 amino acids, the same domain that binds to RCBTB1 and other substrate adaptors; (ii) UbcM2 does not bind mutants of CUL3 that are deficient in substrate adaptor recruitment; (iii) UbcM2 interacts with CUL3 independent of a bridging RING-finger protein; and (iv) can engage the neddylated (i.e., activated) form of CUL3. We also present evidence that UbcM2 can bind to the N-terminal halves of multiple cullins, implying that this E2 is a general cofactor for this class of ligases. Together, these studies represent the first evidence that UbcM2, in concert with substrate adaptors, engages activated CUL3 ligases, thus suggesting that class III E2s are novel regulators of cullin ligases.

ASB2 targets filamins A and B to proteasomal degradation

The ordered series of proliferation and differentiation from hematopoietic progenitor cells is disrupted in leukemia, resulting in arrest of differentiation at immature proliferative stages. Characterizing the molecular basis of hematopoietic differentiation is therefore important for understanding and treating disease. Retinoic acid induces expression of ankyrin repeat-containing protein with a suppressor of cytokine signaling box 2 (ASB2) in acute promyelocytic leukemia cells, and ASB2 expression inhibits growth and promotes commitment, recapitulating an early step critical for differentiation. ASB2 is the specificity subunit of an E3 ubiquitin ligase complex and is proposed to exert its effects by regulating the turnover of specific proteins; however, no ASB2 substrates had been identified. Here, we report that ASB2 targets the actin-binding proteins filamin A and B for proteasomal degradation. Knockdown of endogenous ASB2 in leukemia cells delays retinoic acid-induced differentiation and filamin degradation; conversely, ASB2 expression in leukemia cells induces filamin degradation. ASB2 expression inhibits cell spreading, and this effect is recapitulated by knocking down both filamin A and filamin B. Thus, we suggest that ASB2 may regulate hematopoietic cell differentiation by modulating cell spreading and actin remodeling through targeting of filamins for degradation.