NEDD4: a promising target for cancer therapy

E3 ubiquitin ligase NEDD4 induces endocytosis and lysosomal sorting of connexin43 to promote loss of gap junctions

Intercellular communication via gap junctions has an important role in controlling cell growth and in maintaining tissue homeostasis. Connexin43 is the most abundantly expressed gap junction channel protein in humans and acts as a tumor suppressor in multiple tissue types. Connexin43 is often dysregulated at the post-translational level during cancer development, resulting in loss of gap junctions. However, the molecular basis underlying the aberrant regulation of connexin43 in cancer cells has remained elusive. Here, we demonstrate that the oncogenic E3 ubiquitin ligase NEDD4 regulates the connexin43 protein level in HeLa cells, both under basal conditions and in response to protein kinase C activation. Furthermore, overexpression of NEDD4, but not a catalytically inactive form of NEDD4, was found to result in nearly complete loss of gap junctions and increased lysosomal degradation of connexin43 in both HeLa and C33A cervical carcinoma cells. Collectively, the data provide new insights into the molecular basis underlying the regulation of gap junction size and represent the first evidence that an oncogenic E3 ubiquitin ligase promotes loss of gap junctions and connexin43 degradation in human carcinoma cells.

A quinazoline-based HDAC inhibitor affects gene expression pathways involved in cholesterol biosynthesis and mevalonate in prostate cancer cells

Chronic inflammation can lead to the development of cancers and resolution of inflammation is an ongoing challenge. Inflammation can result from dysregulation of the epigenome and a number of compounds that modify the epigenome are in clinical use. In this study the anti-inflammatory and anti-cancer effects of a quinazoline epigenetic-modulator compound were determined in prostate cancer cell lines using a non-hypothesis driven transcriptomics strategy utilising the Affymetrix PrimeView® Human Gene Expression microarray. GATHER and IPA software were used to analyse the data and to provide information on significantly modified biological processes, pathways and networks. A number of genes were differentially expressed in both PC3 and DU145 prostate cancer cell lines. The top canonical pathways that frequently arose across both cell lines at a number of time points included cholesterol biosynthesis and metabolism, and the mevalonate pathway. Targeting of sterol and mevalonate pathways may be a powerful anticancer approach.

Indole-3-carbinol (I3C) analogues are potent small molecule inhibitors of NEDD4-1 ubiquitin ligase activity that disrupt proliferation of human melanoma cells

The HECT domain-containing E3 ubiquitin ligase NEDD4-1 (Neural precursor cell Expressed Developmentally Down regulated gene 4-1) is frequently overexpressed in human cancers and displays oncogenic-like properties through the ubiquitin-dependent regulation of multiple protein substrates. However, little is known about small molecule enzymatic inhibitors of HECT domain-containing ubiquitin ligases. We now demonstrate that indole-3-carbinol (I3C), a natural anti-cancer phytochemical derived from cruciferous vegetables such as cabbage and broccoli, represents a new chemical scaffold of small molecule enzymatic inhibitors of NEDD4-1. Using in vitro ubiquitination assays, I3C, its stable synthetic derivative 1-benzyl-I3C and five novel synthetic analogues were shown to directly inhibit NEDD4-1 ubiquitination activity. Compared to I3C, which has an IC50 of 284μM, 1-benzyl-I3C was a significantly more potent NEDD4-1 enzymatic inhibitor with an IC50 of 12.3μM. Compounds 2242 and 2243, the two indolecarbinol analogues with added methyl groups that results in a more nucleophilic benzene ring π system, further enhanced potency with IC50s of 2.71μM and 7.59μM, respectively. Protein thermal shift assays that assess small ligand binding, in combination with in silico binding simulations with the crystallographic structure of NEDD4-1, showed that each of the indolecarbinol compounds bind to the purified catalytic HECT domain of NEDD4-1. The indolecarbinol compounds inhibited human melanoma cell proliferation in a manner that generally correlated with their effectiveness as NEDD4-1 enzymatic inhibitors. Taken together, we propose that I3C analogues represent a novel set of anti-cancer compounds for treatment of human melanomas and other cancers that express indolecarbinol-sensitive target enzymes.

Mimicking the phosphorylation of Rsp5 in PKA site T761 affects its function and cellular localization

Rsp5 ubiquitin ligase belongs to the Nedd4 family of proteins, which affect a wide variety of processes in the cell. Here we document that Rsp5 shows several phosphorylated variants of different mobility and the migration of the phosphorylated forms of Rsp5 was faster for the tpk1Δ tpk3Δ mutant devoid of two alternative catalytic subunits of protein kinase A (PKA), indicating that PKA possibly phosphorylates Rsp5 in vivo. We demonstrated by immunoprecipitation and Western blot analysis of GFP-HA-Rsp5 protein using the anti-phospho PKA substrate antibody that Rsp5 is phosphorylated in PKA sites. Rsp5 contains the sequence 758-RRFTIE-763 with consensus RRXS/T in the catalytic HECT domain and four other sites with consensus RXXS/T, which might be phosphorylated by PKA. The strain bearing the T761D substitution in Rsp5 which mimics phosphorylation grew more slowly at 28°C and did not grow at 37°C, and showed defects in pre-tRNA processing and protein sorting. The rsp5-T761D strain also demonstrated a reduced ability to form colonies, an increase in the level of reactive oxygen species (ROS) and hypersensitivity to ROS-generating agents. These results indicate that PKA may downregulate many functions of Rsp5, possibly affecting its activity. Rsp5 is found in the cytoplasm, nucleus, multivesicular body and cortical patches. The rsp5-T761D mutation led to a strongly increased cortical localization while rsp5-T761A caused mutant Rsp5 to locate more efficiently in internal spots. Rsp5-T761A protein was phosphorylated less efficiently in PKA sites under specific growth conditions. Our data suggests that Rsp5 may be phosphorylated by PKA at position T761 and that this regulation is important for its localization and function.

Elevated expression of NEDD9 is associated with metastatic activity in gastric cancer

Objective

To investigate the protein and mRNA expression of NEDD9 in gastric cancer (GC) tissues, adjacent atypical hyperplasia tissues, and normal gastric mucosa tissues, and analyze its relationship with the pathological features and prognosis of GC.

Methods

Forty cases of GC tissues, 20 cases of adjacent atypical hyperplasia tissues, and 40 cases of normal gastric mucous tissues were collected. Immunohistochemistry and Western blot were used to examine the expression of NEDD9 protein in various tissues. Situ hybridization and reverse transcription polymerase chain reaction were applied to detect the expression of NEDD9 mRNA in various tissues. The correlation of NEDD9 expression with invasion and metastasis of GC was analyzed.

Results

The protein expression level of NEDD9 was significantly higher in GC tissues than in adjacent atypical hyperplasia tissues and normal gastric mucous tissues (P<0.05). The protein expression level of NEDD9 was positively related to the invasion depth of carcinoma and tumor lymph node metastasis (P<0.05), but unrelated to age, sex, tumor size, and clinical classification of cancer (P<0.05). The mRNA expression level of NEDD9 was also significantly higher in GC tissues than in adjacent atypical hyperplasia tissues and normal gastric mucous tissues (P<0.05), and positively related with the tumor lymph node metastasis and invasion depth of carcinoma (P<0.05).

Conclusion

NEDD9 is involved in the occurrence and development of GC, and it may be an important biological marker of GC metastasis and infiltration.

The Novel Functions of High-Molecular-Mass Complexes Containing Insulin Receptor Substrates in Mediation and Modulation of Insulin-Like Activities: Emerging Concept of Diverse Functions by IRS-Associated Proteins

Insulin-like peptides, such as insulin-like growth factors (IGFs) and insulin, induce a variety of bioactivities, such as growth, differentiation, survival, increased anabolism, and decreased catabolism in many cell types and in vivo. In general, IGFs or insulin bind to IGF-I receptor (IGF-IR) or insulin receptor (IR), activating the receptor tyrosine kinase. Insulin receptor substrates (IRSs) are known to be major substrates of receptor kinases, mediating IGF/insulin signals to direct bioactivities. Recently, we discovered that IRSs form high-molecular-mass complexes (referred to here as IRSomes) even without IGF/insulin stimulation. These complexes contain proteins (referred to here as IRSAPs; IRS-associated proteins), which modulate tyrosine phosphorylation of IRSs by receptor kinases, control IRS stability, and determine intracellular localization of IRSs. In addition, in these complexes, we found not only proteins that are involved in RNA metabolism but also RNAs themselves. Thus, IRSAPs possibly contribute to modulation of IGF/insulin bioactivities. Since it is established that disorder of modulation of insulin-like activities causes various age-related diseases including cancer, we could propose that the IRSome is an important target for treatment of these diseases.

Regulation of the Tumor-Suppressor Function of the Class III Phosphatidylinositol 3-Kinase Complex by Ubiquitin and SUMO

The occurrence of cancer is often associated with a dysfunction in one of the three central membrane-involution processes—autophagy, endocytosis or cytokinesis. Interestingly, all three pathways are controlled by the same central signaling module: the class III phosphatidylinositol 3-kinase (PI3K-III) complex and its catalytic product, the phosphorylated lipid phosphatidylinositol 3-phosphate (PtdIns3P). The activity of the catalytic subunit of the PI3K-III complex, the lipid-kinase VPS34, requires the presence of the membrane-targeting factor VPS15 as well as the adaptor protein Beclin 1. Furthermore, a growing list of regulatory proteins associates with VPS34 via Beclin 1. These accessory factors define distinct subunit compositions and thereby guide the PI3K-III complex to its different cellular and physiological roles. Here we discuss the regulation of the PI3K-III complex components by ubiquitination and SUMOylation. Especially Beclin 1 has emerged as a highly regulated protein, which can be modified with Lys11-, Lys48- or Lys63-linked polyubiquitin chains catalyzed by distinct E3 ligases from the RING-, HECT-, RBR- or Cullin-type. We also point out other cross-links of these ligases with autophagy in order to discuss how these data might be merged into a general concept.

NEDD4: The founding member of a family of ubiquitin-protein ligases

Ubiquitination plays a crucial role in regulating proteins post-translationally. The focus of this review is on NEDD4, the founding member of the NEDD4 family of ubiquitin ligases that is evolutionarily conserved in eukaryotes. Many potential substrates of NEDD4 have been identified and NEDD4 has been shown to play a critical role in the regulation of a number of membrane receptors, endocytic machinery components and the tumour suppressor PTEN. In this review we will discuss the diverse pathways in which NEDD4 is involved, and the patho-physiological significance of this important ubiquitin ligase.

Targeting the ubiquitin pathway for cancer treatment

Proteasome-mediated degradation is a common mechanism by which cells renew their intracellular proteins and maintain protein homeostasis. In this process, the E3 ubiquitin ligases are responsible for targeting specific substrates (proteins) for ubiquitin-mediated degradation. However, in cancer cells, the stability and the balance between oncoproteins and tumor suppressor proteins are disturbed in part due to deregulated proteasome-mediated degradation. This ultimately leads to either stabilization of oncoprotein(s) or increased degradation of tumor suppressor(s), contributing to tumorigenesis and cancer progression. Therefore, E3 ubiquitin ligases including the SCF types of ubiquitin ligases have recently evolved as promising therapeutic targets for the development of novel anti-cancer drugs. In this review, we highlighted the critical components along the ubiquitin pathway including E1, E2, various E3 enzymes and DUBs that could serve as potential drug targets and also described the available bioactive compounds that target the ubiquitin pathway to control various cancers.