AMBRA1 Interplay with Cullin E3 Ubiquitin Ligases Regulates Autophagy Dynamics

The suppressor of cytokine signalling (SOCS) box was first identified in the SH2-containing SOCS box family (cytokine-inducible SH2-containing protein, SOCS1-7) and is a 40-amino acid motif, which functions to recruit an E3 ubiquitin ligase complex consisting of the adapter proteins elongins B and C, Rbx2 and the scaffold protein Cullin5. The SOCS box is found in a diverse array of intracellular signalling molecules, many of which contain different protein interaction domains such as SPRY and WD40 domains, leucine and ankyrin repeats or other functional domains such as GTPases. In general, the SOCS box-containing proteins are thought to act as substrate-recognition modules to mediate the polyubiquitination and subsequent degradation of substrate proteins by the 26S proteasome.

https://iubmb.onlinelibrary.wiley.com/doi/pdf/10.1002/iub.1011

The SOCS box-adapting proteins for ubiquitination and proteasomal degradation.

The Elongin complex was originally identified as a positive regulator of RNA polymerase II and is composed of a transcriptionally active subunit (A) and two regulatory subunits (B and C). The Elongin BC complex enhances the transcriptional activity of Elongin A. “Classical” SOCS box-containing proteins interact with the Elongin BC complex and have ubiquitin ligase activity. They also interact with the scaffold protein Cullin (Cul) and the RING domain protein Rbx and thereby are members of the Cullin RING ligase (CRL) superfamily. The Elongin BC complex acts as an adaptor connecting Cul and SOCS box proteins. Recently, it was demonstrated that classical SOCS box proteins can be further divided into two groups, Cul2- and Cul5-type proteins. The classical SOCS box-containing protein pVHL is now classified as a Cul2-type protein. The Elongin BC complex containing CRL family is now considered two distinct protein assemblies, which play an important role in regulating a variety of cellular processes such as tumorigenesis, signal transduction, cell motility, and differentiation.

/pdf/the-role-of-elongin-bc-containing-ubiquitin-ligases-2gl09tfa9g.pdf

The Role of Elongin BC-Containing Ubiquitin Ligases.

Extracellular vesicles (EVs) are commonly used by normal and tumor cells for communication at long distances to exchange by complex molecular messages and deliver a variety of essential biomolecules. EVs (exosomes and microvesicles) released in large numbers by glioma cells represent a key mechanism of intercellular signaling. Tumor-derived EVs are produced to regulate all vital functions of tumor cells including growth, proliferation, migration, survival, malignancy, invasion, and resistance to host anti-tumor immunity and anti-cancer drugs. Glioma EVs were shown to carry a variety of biomolecules such as oncogenic growth factors, receptors, enzymes, transcription factors, signaling and immunomodulatory molecules, DNA of mutated and nonmutated oncogenes, RNA transcripts, and noncoding RNA including retrotransposons, vault RNA, and microRNAs. Glioma-derived EVs can be useful as a source of potential tumor-associated biomarkers essential for development and validation of new diagnostic and prognostic tools for glioma and glioblastoma. Tumor EVs are enriched with glioma antigens that could be helpful, for example, for development of new advanced anti-tumor immune vaccines based on autologous dendritic cells stimulated by tumor-specific antigens.

Extracellular vesicles shed by glioma cells: pathogenic role and clinical value.

The suppressor of cytokine signaling (SOCS) box consists of the BC box and the cullin 5 (Cul5) box, which interact with Elongin BC and Cul5, respectively. SOCS box-containing proteins have ubiquitin ligase activity mediated by the formation of a complex with the scaffold protein Cul5 and the RING domain protein Rbx2, and are thereby members of the cullin RING ligase superfamily. Cul5-type ubiquitin ligases have a variety of substrates that are targeted for polyubiquitination and proteasomal degradation. Here, we review the current knowledge on the identification of Cul5 and the regulation of its expression, as well as the signaling pathways regulated by Cul5 and how viruses highjack the Cul5 system to overcome antiviral responses.

/pdf/the-role-of-cullin-5-containing-ubiquitin-ligases-qlpr9atfh1.pdf

The role of cullin 5-containing ubiquitin ligases.

Notch signaling controls multiple developmental processes, thus demanding versatile functions. We have previously shown that this may be partly achieved by accelerating ubiquitin-mediated degradation of important regulators of differentiation. However, the underlying mechanism was unknown. We now find that Notch signaling transcriptionally activates the gene encoding ankyrin-repeat SOCS box-containing protein 2 (Asb2). Asb2 promotes the ubiquitination of Notch targets such as E2A and Janus kinase (Jak) 2, and a dominant-negative (DN) mutant of Asb2 blocks Notch-induced degradation of these proteins. Asb2 likely binds Jak2 directly but associates with E2A through Skp2. We next provide evidence to suggest that Asb2 bridges the formation of non-canonical cullin-based complexes through interaction with not only ElonginB/C and Cullin (Cul) 5, but also the F-box-containing protein, Skp2, which is known to associate with Skp1 and Cul1. Consistently, ablating the function of Cul1 or Cul5 using DN mutants or siRNAs protected both E2A and Jak2 from Asb2-mediated or Notch-induced degradation. By shifting monomeric E3 ligase complexes to dimeric forms through activation of Asb2 transcription, Notch could effectively control the turnover of a variety of substrates and it exerts diverse effects on cell proliferation and differentiation.

/pdf/notch-induced-asb2-expression-promotes-protein-2tpuqx0mr9.pdf

Notch-induced Asb2 expression promotes protein ubiquitination by forming non-canonical E3 ligase complexes

Simple Summary Outcomes for patients with osteosarcoma have remained stagnant for more than 3 decades. Novel therapeutic agents are desperately needed. Osteosarcoma cells often express abnormal form of the p53, p63, and p73 genes, which promote glucose uptake, cell glycolysis, and rapid proliferation. Pramlintide, an FDA-approved drug for type 2 diabetes, interfered with tumor glycolysis leading to decreased cell growth and increased cell death. When we injected Pramlintide into osteosarcoma tumor nodules of the mice, the tumors were significantly smaller after 21 days while the control tumors continued to grow. Tumor hypoxia was also decreased. This is the first report showing the potential efficacy of Pramlintide against osteosarcoma, indicating that Pramlintide may be a novel therapeutic approach for patients with relapsed osteosarcoma. Abstract Despite aggressive combination chemotherapy and surgery, outcomes for patients with osteosarcoma have remained stagnant for more than 25 years, and numerous clinical trials have identified no new therapies. p53 deletion or mutation is found in more than 80% of osteosarcoma tumors. In p53-deficient cancers with structurally altered p63 and p73, interfering with tumor cell metabolism using Pramlintide (an FDA-approved drug for type 2 diabetes) results in tumor regression. Pramlintide response is mediated through upregulation of islet amyloid polypeptide (IAPP). Here, we showed that osteosarcoma cells have altered p63, p73, and p53, and decreased IAPP expression but have the two main IAPP receptors, CalcR and RAMP3, which inhibit glycolysis and induce apoptosis. We showed that in osteosarcoma cells with high- or mid-range glycolytic activity, Pramlintide decreased cell glycolysis, resulting in decreased proliferation and increased apoptosis in vitro. In contrast, Pramlintide had no effect in osteosarcoma cells with low glycolytic activity. Using a subcutaneous osteosarcoma mouse model, we showed that intratumoral injection of Pramlintide-induced tumor regression. Tumor sections showed increased apoptosis and a decrease in Ki-67 and HIF-1α. These data suggest that in osteosarcoma cells with altered p53, p63, and p73 and a high glycolytic function, Pramlintide therapy can modulate metabolic programming and inhibit tumor growth.

/pdf/pramlintide-a-novel-therapeutic-approach-for-osteosarcoma-21adyis9.pdf

Yuan Zheng Yang

Papers

Notch-induced Asb2 expression promotes protein ubiquitination by forming non-canonical E3 ligase complexes

Pramlintide: A Novel Therapeutic Approach for Osteosarcoma through Metabolic Reprogramming