Protein-coding and microRNA biomarkers of recurrence of prostate cancer following radical prostatectomy.

An important challenge in prostate cancer research is to develop effective predictors of tumor recurrence following surgery to determine whether immediate adjuvant therapy is warranted. To identify biomarkers predictive of biochemical recurrence, we isolated the RNA from 70 formalin-fixed, paraffin-embedded radical prostatectomy specimens with known long-term outcomes to perform DASL expression profiling with a custom panel that we designed of 522 prostate cancer-relevant genes. We identified a panel of 10 protein-coding genes and two miRNA genes (RAD23B, FBP1, TNFRSF1A, CCNG2, NOTCH3, ETV1, BID, SIM2, LETMD1, ANXA1, miR-519d, and miR-647) that could be used to separate patients with and without biochemical recurrence (P < 0.001), as well as for the subset of 42 Gleason score 7 patients (P < 0.001). We performed an independent validation analysis on 40 samples and found that the biomarker panel was also significant at prediction of biochemical recurrence for all cases (P = 0.013) and for a subset of 19 Gleason score 7 cases (P = 0.010), both of which were adjusted for relevant clinical information including T-stage, prostate-specific antigen, and Gleason score. Importantly, these biomarkers could significantly predict clinical recurrence for Gleason score 7 patients. These biomarkers may increase the accuracy of prognostication following radical prostatectomy using formalin-fixed specimens.

Effects of partner proteins on BCA2 RING ligase activity.

BACKGROUND: BCA2 is an E3 ligase linked with hormone responsive breast cancers. We have demonstrated previously that the RING E3 ligase BCA2 has autoubiquitination activity and is a very unstable protein. Previously, only Rab7, tetherin, ubiquitin and UBC9 were known to directly interact with BCA2. METHODS: Here, additional BCA2 binding proteins were found using yeast two-hybrid and bacterial-II-hybrid screening techniques with Human breast and HeLa cDNA libraries. Co-expression of these proteins was analyzed through IHC of TMAs. Investigation of the molecular interactions and effects were examined through a series of in vivo and in vitro assays. RESULTS: Ten unique BCA2 interacting proteins were identified, two of which were hHR23a and 14-3-3sigma. Both hHR23a and 14-3-3sigma are co-expressed with BCA2 in breast cancer cell lines and patient breast tumors (n = 105). hHR23a and BCA2 expression was significantly correlated (P = < 0.0001 and P = 0.0113) in both nucleus and cytoplasm. BCA2 expression showed a statistically significant correlation with tumor grade. High cytoplasmic hHR23a trended towards negative nodal status. Binding to BCA2 by hHR23a and 14-3-3sigma was confirmed in vitro using tagged partner proteins and BCA2. hHR23a and 14-3-3sigma effect the autoubiquitination and auto-degradation activity of BCA2. Ubiquitination of hHR23a-bound BCA2 was found to be dramatically lower than that of free BCA2, suggesting that hHR23a promotes the stabilization of BCA2 by inactivating its autoubiquitination activity, without degradation of hHR23a. On the other hand, phosphorylated BCA2 protein is stabilized by interaction with 14-3-3sigma both with and without proteasome inhibitor MG-132 suggesting that BCA2 is regulated by multiple degradation pathways. CONCLUSIONS: The interaction between BCA2 and hHR23a in breast cancer cells stabilizes BCA2. High expression of BCA2 is correlated with grade in breast cancer, suggesting regulation of this E3 ligase is important to cancer progression.

The RING finger protein11 binds to Smad4 and enhances Smad4-dependant TGF-beta signalling.

BACKGROUND: In breast carcinomas, prolonged signalling through the TGF-beta receptor promotes latent tumour progression, metastasis and the epithelial-to-mesenchymal transition of tumour cells. Previously, it has been found that the 154 amino acid RING finger protein, RNF11, was overexpressed in high-grade breast tumours and was capable of modulating TGF-beta signalling. MATERIALS AND METHODS: Utilizing cellular and biochemical assays, key interactions and molecular roles for the RNF11 protein in the TGF-beta pathway were explored. RESULTS: It is shown that RNF11 is required for TGF-beta signalling and is capable of enhancing the Smad-TGF-beta signalling pathway directly. Further, that endogenous RNF11 and Smad4 proteins associate and co-localize in a TGF-beta-enhanced manner. This study indicates that RNF11 induces an increase in Smad4 protein levels. In functional assays, it is observed that RNF11 enhances Smad4-dependant TGF-beta signalling and that RNF11 alone can recapitulate Smad4-dependant apoptosis in cellular assays. CONCLUSION: RNF11 acts directly on Smad4 to enhance Smad4 function, and plays a role in prolonged TGF-beta signalling and possibly in latent tumour progression.

Genetic and expression aberrations of E3 ubiquitin ligases in human breast cancer.

Recent studies revealed that E3 ubiquitin ligases play important roles in breast carcinogenesis. Clinical research studies have found that (epi)-genetic (deletion, amplification, mutation, and promoter methylation) and expression aberration of E3s are frequent in human breast cancer. Furthermore, many studies have suggested that many E3s are either oncogenes or tumor suppressor genes in breast cancer. In this review, we provide a comprehensive summary of E3s, which have genetic and/or expression aberration in breast cancer. Most cancer-related E3s regulate the cell cycle, p53, transcription, DNA repair, cell signaling, or apoptosis. An understanding of the oncogenic potential of the E3s may facilitate identifying and developing individual E3s as diagnosis markers and drug targets in breast cancer.

IL-6 enhances the nuclear translocation of DNA cytosine-5-methyltransferase 1 (DNMT1) via phosphorylation of the nuclear localization sequence by the AKT kinase.

The epigenetic programming of genomic DNA is accomplished, in part, by several DNA cytosine-5-methyltransferases that act by covalently modifying cytosines with the addition of a methyl group. This covalent modification is maintained by the DNA cytosine-5-methyltransferase-1 enzyme (DNMT1), which is capable of acting in concert with other similar enzymes to silence important tumor suppressor genes. IL-6 is a multifunctional mediator of inflammation, acting through several major signaling cascades, including the phosphatidylinositol-3-kinase pathway (PI-3-K), which activates protein kinase B (AKT/PKB) downstream. Here, we show that the subcellular localization of DNMT1 can be altered by the addition of IL-6, increasing the rate of nuclear translocation of the enzyme from the cytosolic compartment. The mechanism of nuclear translocation of DNMT1 is greatly enhanced by phosphorylation of the DNMT1 nuclear localization signal (NLS) by PKB/AKT kinase. Mutagenic alteration of the two AKT target amino acids within the NLS results in a major loss of DNMT1 nuclear translocation, while the creation of a "phospho-mimic" amino acid (mutation to acidic residues) restores this compartmentation ability. These observations suggest an interesting hypothesis regarding how mediators of chronic inflammation may disturb the delicate balance of cellular compartmentalization of important proteins, and reveals a potential mechanism for the induction or enhancement of tumor growth via alteration of the components involved in the epigenetic programming of a cell.

A novel RING-type ubiquitin ligase breast cancer-associated gene 2 correlates with outcome in invasive breast cancer.

The RING finger family of proteins possess ubiquitin ligase activity and play pivotal roles in protein degradation and receptor-mediated endocytosis. In this study, we examined whether the breast cancer-associated gene 2 (BCA2), a novel RING domain protein, has E3 ubiquitin ligase activity and investigated its expression status in breast tumors. The full-length BCA2 gene was cloned from the human breast cancer cell line MDA-MB-468. It encodes an open reading frame of 304 amino acids and contains a RING-H2 domain. BCA2 maps to chromosome 1q21.1, a region known to harbor cytogenetic aberrations in breast cancers. We found that the BCA2 protein has an intrinsic autoubiquitination activity, the hallmark of E3 ligases, whereas mutant RING protein is not autoubiquitinated. This indicates that the BCA2 ubiquitin ligase activity is dependent on the RING-H2 domain. Using tissue microarrays and immunohistochemistry, we found strong to intermediate BCA2 staining in 56% of 945 invasive breast cancers cases, which was significantly correlated with positive estrogen receptor status [odds ratio (OR), 1.51; P = 0.004], negative lymph node status (OR, 0.73; P = 0.02), and an increase in disease-free survival for regional recurrence (OR, 0.45; P = 0.03). Overexpression of BCA2 increased proliferation and small interfering RNA inhibited growth of T47D human breast cancer cells and NIH3T3 mouse cells. The autoubiquitination activity of BCA2 indicates that it is a novel RING-type E3 ligase. Its association with clinical measures and its effects on cell growth indicate that BCA2 may be important for the ubiquitin modification of proteins crucial to breast carcinogenesis and growth.

Essential roles of IGFBP-3 and IGFBP-rP1 in breast cancer.

Insulin and insulin-like growth factors (IGFs) have critical functions in growth regulatory signalling pathways. They are part of a tightly controlled network of ligands, receptors, binding proteins and their proteases. However, the system becomes uncontrolled in neoplasia. The insulin-like growth factor binding protein 3 (IGFBP-3) and the insulin-like growth factor binding protein-related protein 1 (IGFBP-rP1) have unique properties among the sixteen known members of the IGFBP superfamily. IGFBP-3 has very high affinity for IGFs (k(d) approximately 10(-10) M), it transports >75% of serum IGF-I and -II, whereas it's affinity for insulin is very low. On the other hand, IGFBP-rP1 binds insulin with very high affinity (500-fold higher compared to other IGFBPs), but has low affinity for IGF-I and -II proteins (k(d) = 3 x 10(-8) M). In this review, we have examined the roles of IGFBP-3 and IGFBP-rP1 in breast cancer, and discuss the potential impact of these two proteins in mammary carcinoma risk assessment and the development of treatments for breast cancer.

The ubiquitin-mediated protein degradation pathway in cancer: therapeutic implications.

The highly conserved eukaryotic ubiquitin-proteasome system (UP-S) plays a pivotal role in protein homeostasis and is critical in regulating normal and cancer-related cellular processes. The hierarchical nature of the UP-S provides a rich source of molecular targets for specific intervention and has therefore arisen as a promising approach to innovative anticancer therapies. The first in class proteasome inhibitory agent Bortezomib (Velcade) has recently obtained regulatory approval for the treatment of multiple myeloma. Ubiquitin-mediated degradation is a complex process that is comprised of well defined steps involving ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s) and ubiquitin ligases (E3s). Although a single E1 activates the ubiquitin conjugation machinery, a large number of E2 conjugating enzymes and E3 ligases are now known to exist. Proteins tagged with ubiquitin are subsequently recognised by the proteasome for digestion and fragmentation. The enzymatic nature, multitude of E3s and their specific substrate recognition predestines them as therapeutic targets. This article will review known inhibitors of the proteasome and their molecular mechanisms as well as ongoing developments and promising avenues for targeting substrate-specific E3 ligases that are likely to yield a new class of therapeutics that will serve and complement the armamentarium of anticancer drugs.

Global transcriptome analysis of formalin-fixed prostate cancer specimens identifies biomarkers of disease recurrence.

Prostate cancer remains the second leading cause of cancer death in American men and there is an unmet need for biomarkers to identify patients with aggressive disease. In an effort to identify biomarkers of recurrence, we performed global RNA sequencing on 106 formalin-fixed, paraffin-embedded prostatectomy samples from 100 patients at three independent sites, defining a 24-gene signature panel. The 24 genes in this panel function in cell-cycle progression, angiogenesis, hypoxia, apoptosis, PI3K signaling, steroid metabolism, translation, chromatin modification, and transcription. Sixteen genes have been associated with cancer, with five specifically associated with prostate cancer (BTG2, IGFBP3, SIRT1, MXI1, and FDPS). Validation was performed on an independent publicly available dataset of 140 patients, where the new signature panel outperformed markers published previously in terms of predicting biochemical recurrence. Our work also identified differences in gene expression between Gleason pattern 4 + 3 and 3 + 4 tumors, including several genes involved in the epithelial-to-mesenchymal transition and developmental pathways. Overall, this study defines a novel biomarker panel that has the potential to improve the clinical management of prostate cancer.

Regulation of metformin response by breast cancer associated gene 2.

Adenosine monophosphate-activated protein kinase (AMPK), a master regulator of cellular energy homeostasis, has emerged as a promising molecular target in the prevention of breast cancer. Clinical trials using the United States Food and Drug Administration (FDA)-approved, AMPK-activating, antidiabetic drug metformin are promising in this regard, but the question of why metformin is protective for some women but not others still remains. Breast cancer associated gene 2 (BCA2/Rabring7/RNF115), a novel Really Interesting New Gene (RING) finger ubiquitin E3 ligase, is overexpressed in >50% of breast tumors. Herein, we report that BCA2 is an endogenous inhibitor of AMPK activation in breast cancer cells and that BCA2 inhibition increases the efficacy of metformin. BCA2 overexpression inhibited both basal and inducible Thr172 phosphorylation/activation of AMPKα1, while BCA2-specific small interfering RNA (siRNA) enhanced phosphorylated AMPKα1 (pAMPKα1). The AMPK-suppressive function of BCA2 requires its E3 ligase-specific RING domain, suggesting that BCA2 targets some protein controlling (de)phosphorylation of AMPKα1 for degradation. Activation of AMPK by metformin triggered a growth inhibitory signal but also increased BCA2 protein levels, which correlated with AKT activation and could be curbed by an AMPK inhibitor, suggesting a potential feedback mechanism from pAMPKα1 to pAkt to BCA2. Finally, BCA2 siRNA, or inhibition of its upstream stabilizing kinase AKT, increased the growth inhibitory effect of metformin in multiple breast cancer cell lines, supporting the conclusion that BCA2 weakens metformin's efficacy. Our data suggest that metformin in combination with a BCA2 inhibitor may be a more effective breast cancer treatment strategy than metformin alone.

RNF115/BCA2 E3 ubiquitin ligase promotes breast cancer cell proliferation through targeting p21Waf1/Cip1 for ubiquitin-mediated degradation.

The E3 ubiquitin ligase RING finger protein 115 (RNF115), also known as breast cancer-associated gene 2 (BCA2), has previously been reported to be overexpressed in estrogen receptor α (ERα)-positive breast tumors and to promote breast cell proliferation; however, its mechanism is unknown. In this study, we demonstrated that silencing of BCA2 by small interfering RNAs (siRNAs) in two ERα-positive breast cancer cell lines, MCF-7 and T47D, decreases cell proliferation and increases the protein levels of the cyclin-dependent kinase inhibitor p21Waf/Cip1. The protein stability of p21 was negatively regulated by BCA2. BCA2 directly interacts with p21 and promotes p21 ubiquitination and proteasomal degradation. Knockdown of p21 partially rescues the cell growth arrest induced by the BCA2 siRNA. These results suggest that BCA2 promotes ERα-positive breast cancer cell proliferation at least partially through downregulating the expression of p21.

Role of the BCA2 ubiquitin E3 ligase in hormone responsive breast cancer.

The BCA2 protein contains a RING H2 finger and a Zn finger near the N-terminus and has E3 ligase activity. RING finger proteins play critical roles in mediating the transfer of ubiquitin and ubiquitin like modifiers to heterologous substrates as well as to the RING finger proteins themselves. Protein modification by ubiquitin and small ubiquitin-related modifier (SUMO) plays a pivotal role in protein homeostasis and is critical to regulating basic cellular processes such as proliferation, differentiation, apoptosis, intracellular signaling, and gene-transcriptional regulation. The addition of ubiquitin or SUMO can modulate the ability of proteins to interact with their partners, alter their patterns of sub-cellular localization and control their stability. It is clear that SUMO influences many different biological processes however recent data suggest that it is specifically important in the regulation of transcription. BCA2 is an E3 ligase that interacts with the SUMO conjugating enzyme Ubc9. It could therefore function as an E3 in the sumoylation of various transcription factors. We have found that the BCA2 is co-expressed with the estrogen receptor in 74% of ER-positive invasive ductal carcinomas from a 635 member breast cancer cohort (p = 0.004). At the cellular level, BCA2 co-localizes with ER and it appears that at the transcriptional level BCA2 mRNA expression is regulated by estrogen. Bioinformatic analysis of the BCA2 promoter region revealed ER and PR binding sites as well as that of other more general transcription factors. The data presented here provides an overview of the potential involvement of the BCA2 in hormone responsive breast cancer and opens up avenues that should be exploited to better understand the regulation of ER expression, growth of breast cancer cells, and the importance of BCA2.

Novel RING E3 ubiquitin ligases in breast cancer.

Defects in ubiquitin E3 ligases are implicated in the pathogenesis of several human diseases, including cancer, because of their central role in the control of diverse signaling pathways. RING E3 ligases promote the ubiquitination of proteins that are essential to a variety of cellular events. Identification of which ubiquitin ligases specifically affect distinct cellular processes is essential to the development of targeted therapeutics for these diseases. Here we discuss two novel RING E3 ligases, BCA2 and RNF11, that are closely linked to human breast cancer. BCA2 E3 ligase is coregulated with estrogen receptor and plays a role in the regulation of epidermal growth factor receptor (EGF-R) trafficking. RNF11 is a small RING E3 ligase that affects transforming growth factorbeta and EGF-R signaling and is overexpressed in invasive breast cancers. These two proteins demonstrate the complexity of RING E3 ligase interactions in breast cancer and are potential targets for therapeutic interventions.