Speckle type POZ adaptor protein (SPOP) and its role in cancer / La proteína adaptadora Speckle-type POZ (SPOP) y su papel en cáncer

Abstract Proteasomal degradation is an essential regulatory mechanism for cellular homeostasis maintenance. The speckle-type POZ adaptor protein (SPOP) is part of the ubiquitin ligase E3 cullin-3 RING-box1 complex, responsible for the ubiquitination and proteasomal degradation of biomolecules involved in cell cycle control, proliferation, response to DNA damage, epigenetic control, and hormone signaling, among others. Changes in SPOP have been associated with the development of different types of cancer, since it can act as a tumor suppressor mainly in prostate, breast, colorectal, lung cancer and liver cancer, due to point mutations and/or reduced expression, or as an oncogene in kidney cancer by protein overexpression. In endometrial cancer it has a dual role, since it can act as a tumor suppressor or as an oncogene. SPOP is a potential prognostic biomarker and a promising therapeutic target.

Resumen La degradación proteosómica es un mecanismo de regulación esencial para el mantenimiento de la homeostasis celular. La proteína adaptadora Speckle-type POZ (SPOP) hace parte del complejo ubiquitin ligasa E3 cullin-3 RING-box1, encargado de la ubiquitinación y degradación proteosomal de biomoléculas involucradas en el control del ciclo celular, proliferación, respuesta al daño de ADN, control epigenético, señalización hormonal, entre otros. Las alteraciones en SPOP han sido asociadas al desarrollo de diferentes tipos de cáncer, ya que puede actuar como supresor tumoral principalmente en cáncer de próstata, mama, colorrectal y pulmón, debido a mutaciones puntuales y/o expresión reducida o como oncogén en cáncer riñón por sobreexpresión de la proteína. En cáncer endometrial tiene un rol dual, ya que puede actuar como supresor tumoral o como oncogén. SPOP es considerado como un potencial biomarcador pronóstico y un objetivo terapéutico prometedor.

DDB1- and CUL4-associated factor 8 plays a critical role in spermatogenesis / 医学前沿

Cullin-RING E3 ubiquitin ligase (CRL)-4 is a member of the large CRL family in eukaryotes. It plays important roles in a wide range of cellular processes, organismal development, and physiological and pathological conditions. DDB1- and CUL4-associated factor 8 (DCAF8) is a WD40 repeat-containing protein, which serves as a substrate receptor for CRL4. The physiological role of DCAF8 is unknown. In this study, we constructed Dcaf8 knockout mice. Homozygous mice were viable with no noticeable abnormalities. However, the fertility of Dcaf8-deficient male mice was markedly impaired, consistent with the high expression of DCAF8 in adult mouse testis. Sperm movement characteristics, including progressive motility, path velocity, progressive velocity, and track speed, were significantly lower in Dcaf8 knockout mice than in wild-type (WT) mice. However, the total motility was similar between WT and Dcaf8 knockout sperm. More than 40% of spermatids in Dcaf8 knockout mice showed pronounced morphological abnormalities with typical bent head malformation. The acrosome and nucleus of Dcaf8 knockout sperm looked similar to those of WT sperm. In vitro tests showed that the fertilization rate of Dcaf8 knockout mice was significantly reduced. The results demonstrated that DCAF8 plays a critical role in spermatogenesis, and DCAF8 is a key component of CRL4 function in the reproductive system.

Molecular Mechanism of CRBN in the Activity of Lenalidomid eagainst Myeloma--Review / 中国实验血液学杂志

Cereblon（CRBN) is a brain-associated protein with ionic protease activity, which interacts with DNA damage-binding protein-1 (DDB1), Cullin 4 (Cul4A or Cul4B), and regulator of Cullins 1 (RoC1) to form the functional E3 ubiquitin ligase complex(CRBN-CRL4) that performs proteolysis via the ubiquitin-proteasome pathway. And CRBN is a necessary target protein for the anti-myeloma effect of immunomodulators. The combination of lenalidomide and CRBN recruited a new substrate that binds to the CRBN-CRL4 complex, leading to increased ubiquitination and proteasome-dependent degradation, thus resulting in anti-myeloma activity. The substrates binding to this complex are IKZF1, IKZF3 proteins and GS, etc. The CRBN-dependent degradation of IKZF1 and IKZF3 after lenalidomide treatment is also the result of HO-mediated oxidative stress. In addition to ubiquitination, lenalidomide also mediates ubiquitin-independent pathways that prevent CRBN from binding to CD147-MCT1 in a competitive manner to regulate its antitumor activity. Lenalidomide can also play a role in multiple myeloma(MM) cells by modulating miRNA levels and CRBN binding to downstream protein AGO2 expression. Thus, there are many molecular mechanisms of lenalidomide anti-myeloma activity. This review summarizes the molecular mechanisms of CRBN in lenalidomide against myeloma activity in terms of ubiquitin-dependent and ubiquitin-independent pathways.

The CUL4A ubiquitin ligase is a potential therapeutic target in skin cancer and other malignancies / 癌症

Cullin 4A (CUL4A) is an E3 ubiquitin ligase that directly affects DNA repair and cell cycle progression by targeting substrates including damage-specific DNA-binding protein 2 (DDB2), xeroderma pigmentosum complementation group C (XPC), chromatin licensing and DNA replication factor 1 (Cdt1), and p21. Recent work from our laboratory has shown that Cul4a-deficient mice have greatly reduced rates of ultraviolet-induced skin carcinomas. On a cellular level, Cul4a-deficient cells have great capacity for DNA repair and demonstrate a slow rate of proliferation due primarily to increased expression of DDB2 and p21, respectively. This suggests that CUL4A promotes tumorigenesis (as well as accumulation of skin damage and subsequent premature aging) by limiting DNA repair activity and expediting S phase entry. In addition, CUL4A has been found to be up-regulated via gene amplification or overexpression in breast cancers, hepatocellular carcinomas, squamous cell carcinomas, adrenocortical carcinomas, childhood medulloblastomas, and malignant pleural mesotheliomas. Because of its oncogenic activity in skin cancer and up-regulation in other malignancies, CUL4A has arisen as a potential candidate for targeted therapeutic approaches. In this review, we outline the established functions of CUL4A and discuss the E3 ligase's emergence as a potential driver of tumorigenesis.

Research update of Cullin protein in reproductive system / 中国医学科学院学报

Culling protein is a member of Cullin-Ring-based E3-ligases ( CRLs family) , which belong to E3 ubiquitin ligases. Cullin plays diverse and essential roles in many biological processes through mediating the ubiquitination of target proteins. This article summarizes the potential functions of Culling proteins in gamete genesis and maturation, embryo development, and reproductive related disorders.

Phosphorylation of Rictor at Thr1135 impairs the Rictor/Cullin-1 complex to ubiquitinate SGK1

The Rictor/mTOR complex plays a pivotal role in a variety of cellular functions including cellular metabolism, cell proliferation and survival by phosphorylating Akt at Ser473 to fully activate the Akt kinase. However, its upstream regulatory pathways as well as whether it has additional function(s) remain largely unknown. We recently reported that Rictor contains a novel ubiquitin E3 ligase activity by forming a novel complex with Cullin-1, but not with other Cullin family members. Furthermore, we identified SGK1 as its downstream target. Interestingly, Rictor, but not Raptor or mTOR, promotes SGK1 ubiquitination. As a result, SGK1 expression is elevated in Rictor(-/-) MEFs. We further defined that as a feedback mechanism, Rictor can be phosphorylated by multiple AGC family kinases including Akt, S6K and SGK1. Phosphorylation of Rictor at the Thr1135 site did not affect its kinase activity towards phosphorylating its conventional substrates including Akt and SGK1. On the other hand, it disrupted the interaction between Rictor and Cullin-1. Consequently, T1135E Rictor was defective in promoting SGK1 ubiquitination and destruction. This finding further expands our knowledge of Rictor's function. Furthermore, our work also illustrates that Rictor E3 ligase activity could be governed by specific signaling kinase cascades, and that misregulation of this process might contribute to SGK overexpression which is frequently observed in various types of cancers.

Expression of ubiquitin and cullin-1 and its clinicopathological significance in benign and malignant lesions of the lung / 中南大学学报(医学版)

OBJECTIVE@#To investigate the expression of ubiquitin and cullin-1 (cul-1) in benign and malignant lesions of the lung and to determine their clinicopathological significance.@*METHODS@#EnVison immunohistochemistry was used to detect the expression of ubiquitin and cul-1 in the conventional paraffin-embedded sections from the specimens of lung cancer (n = 80) and benign lesion tissues of the lung (n = 20). We also analyzed the relation of the expression of ubiquitin and cul-1 with the clinical stage, differentiation, and with or without lymphatic metastasis.@*RESULTS@#The positive rates of ubiquitin and cul-1 were significantly higher in lung cancer (51.3% and 60.0%) than those in benign lesion tissues of the lung (20.0% and 30.0%; P < 0.05). Positive rates of ubiquitin and cul-1 were all significantly lower in the middle and high-differentiated, Stage I approximately II, and no lymphatic metastasis patients with lung cancer than those in no- or low-differentiated, Stage III approximately IV, and lymphatic metastasis patients with lung cancer tissues (P < 0.01 approximately 0.05). High consistency was found between the positive expression of ubiquitin and cul-1 in lung cancer tissues (chi(2) = 4.04, P < 0.05).@*CONCLUSION@#Expression of ubiquitin and cul-1 in lung cancer tissues may be closely related to the carcinogenesis, progression, clinical biological behaviors, and prognosis of lung cancer.

Cullin4B/E3-ubiquitin ligase negatively regulates beta-catenin.

Beta-catenin is the key transducer of Wingless-type MMTV integration site family member (Wnt) signalling, upregulation of which is the cause of cancer of the colon and other tissues. In the absence of Wnt signals, beta-catenin is targeted to ubiquitin-proteasome-mediated degradation. Here we present the functional characterization of E3-ubiquitin ligase encoded by cul4B. RNAi-mediated knock-down of Cul4B in a mouse cell line C3H T10 (1/2) results in an increase in beta-catenin levels. Loss-of-function mutation in Drosophila cul4 also shows increased beta-catenin/Armadillo levels in developing embryos and displays a characteristic naked-cuticle phenotype. Immunoprecipitation experiments suggest that Cul4B and beta-catenin are part of a signal complex in Drosophila, mouse and human. These preliminary results suggest a conserved role for Cul4B in the regulation of beta-catenin levels.

Identification and characterization of cul-3b, a novel hominine CUL-3 transcript variant / 亚洲男科学杂志(英文版)

<p><b>AIM</b>To identify genes related to the human testis development by substrate hybridization technique.</p><p><b>METHODS</b>A human testis cDNA microarray was constructed and hybridized with probes prepared from human adult and fetal testes and spermatozoa mRNAs by reverse transcription reactions. The differentially expressed genes were sequenced. And a newly identified cullin-3 (CUL-3) transcript variant (designated cul-3b) was bio-informatically analyzed with an online GenBank database. Multi-tissue reverse transcription polymerase chain reaction (RT-PCR) was used to determine the tissue expression profile of cul-3b.</p><p><b>RESULTS</b>Cul-3b, a novel CUL-3 transcript variant, was identified. The expression level of cul-3b in adult testes was 3.79-fold higher than that in fetal ones. Cul-3b differed from cul-3 (including NM_003590 and AY337761) in the opening reading frame and had three internal ribosomal entry sites IRESes in the 5'-UTR. These led to a 24 amino acid (aa) truncation at N-terminus of CUL-3b as compared with CUL-3 and a more motivated expression pattern of cul-3b under some strict circumstances. Additionally, cul-3b expressed ubiquitously in human tissues according to multi-tissue RT-PCR.</p><p><b>CONCLUSION</b>Cul-3b is a novel transcript variant of CUL-3, which may be important not only for the development of human testis but also for that of other organs.</p>