USP15 stabilizes TGF-β receptor I and promotes oncogenesis through the activation of TGF-β signaling in glioblastoma

In advanced cancer, including glioblastoma, the transforming growth factor β (TGF-β) pathway acts as an oncogenic factor and is considered to be a therapeutic target. Using a functional RNAi screen, we identified the deubiquitinating enzyme ubiquitin-specific peptidase 15 (USP15) as a key component of the TGF-β signaling pathway. USP15 binds to the SMAD7-SMAD specific E3 ubiquitin protein ligase 2 (SMURF2) complex and deubiquitinates and stabilizes type I TGF-β receptor (TβR-I), leading to an enhanced TGF-β signal. High expression of USP15 correlates with high TGF-β activity, and the USP15 gene is found amplified in glioblastoma, breast and ovarian cancer. USP15 amplification confers poor prognosis in individuals with glioblastoma. Downregulation or inhibition of USP15 in a patient-derived orthotopic mouse model of glioblastoma decreases TGF-β activity. Moreover, depletion of USP15 decreases the oncogenic capacity of patient-derived glioma-initiating cells due to the repression of TGF-β signaling. Our results show that USP15 regulates the TGF-β pathway and is a key factor in glioblastoma pathogenesis.     

Ubiquitin removal in the TGF-β pathway

The transforming growth factor (TGF-β) pathway is regulated by ubiquitin-mediated proteolysis at different levels. Two studies now identify deubiquitinating enzymes (DUBs) for the TGF-β type I receptor. Both ubiquitin-specific peptidase-4 (USP4) and -15 (USP15) extend the life of activated receptors against the negative pressure of receptor-ubiquitinating complexes, but through distinct modes of action.     

Regulation of the TGF-β pathway by deubiquitinases in cancer

The transforming growth factor-β (TGF-β) pathway regulates diverse cellular processes. It signals via serine/threonine kinase receptors and intracellular Smad and non-Smad effector proteins. In cancer cells, aberrant TGF-β signalling can lead to loss of growth inhibition and an increase in invasion, epithelial-to-mesenchymal transition (EMT) and metastasis. Therapeutic targeting of the pro-oncogenic TGF-β responses is currently being explored as a potential therapy against certain invasive and metastatic cancer types. The ubiquitin post-translational regulation system is emerging as a key regulatory mechanism for the control of TGF-β pathway components. In this review, we focus on the role of deubiquitinases (DUBs), which counteract the activity of E3 ubiquitin ligases. We will discuss the mechanisms by which specific DUBs control Smad and non-Smad TGF-β signalling routes, and how perturbation of the expression and function of DUBs contributes to misregulation of TGF-β signalling in cancer.     

Negative regulation of TGF-β signaling in development

The TGF-β superfamily members have important roles in controlling patterning and tissue formation in both invertebrates and vertebrates. Two types of signal transducers, receptors and Smads, mediate the signaling to regulate expression of their target genes. Despite of the relatively simple signal transduction pathway, many modulators have been found to contribute to a tight regulation of this pathway in a variety of mechanisms. This article reviews the negative regulation of TGF-β signaling with focus on its roles in vertebrate development.     

Evolution of the TGF-β signaling pathway and its potential role in the ctenophore, Mnemiopsis leidyi

The TGF-β signaling pathway is a metazoan-specific intercellular signaling pathway known to be important in many developmental and cellular processes in a wide variety of animals. We investigated the complexity and possible functions of this pathway in a member of one of the earliest branching metazoan phyla, the ctenophore Mnemiopsis leidyi. A search of the recently sequenced Mnemiopsis genome revealed an inventory of genes encoding ligands and the rest of the components of the TGF-β superfamily signaling pathway. The Mnemiopsis genome contains nine TGF-β ligands, two TGF-β-like family members, two BMP-like family members, and five gene products that were unable to be classified with certainty. We also identified four TGF-β receptors: three Type I and a single Type II receptor. There are five genes encoding Smad proteins (Smad2, Smad4, Smad6, and two Smad1s). While we have identified many of the other components of this pathway, including Tolloid, SMURF, and Nomo, notably absent are SARA and all of the known antagonists belonging to the Chordin, Follistatin, Noggin, and CAN families. This pathway likely evolved early in metazoan evolution as nearly all components of this pathway have yet to be identified in any non-metazoan. The complement of TGF-β signaling pathway components of ctenophores is more similar to that of the sponge, Amphimedon, than to cnidarians, Trichoplax, or bilaterians. The mRNA expression patterns of key genes revealed by in situ hybridization suggests that TGF-β signaling is not involved in ctenophore early axis specification. Four ligands are expressed during gastrulation in ectodermal micromeres along all three body axes, suggesting a role in transducing earlier maternal signals. Later expression patterns and experiments with the TGF-β inhibitor SB432542 suggest roles in pharyngeal morphogenesis and comb row organization.     

Expression of Oct4 in HCC and modulation to wnt/β-catenin and TGF-β signal pathways

Hepatocellular carcinoma (HCC) is considered as a disease of dysfunction of the stem cells. Studies on stem cells have demonstrated that Oct4 plays a pivotal role in embryo regulation. In order to understand the role of Oct4 in HCC and the relationship among Oct4 and wnt/β-catenin and TGF-β signal pathways, we have detected the expression of Oct4, Nanog, Sox2, STAT3 as well as the genes in wnt/β-catenin, and TGF-β families in HCC cell lines and in tumor specimens from HCC patients. The authors found that Oct4 was expressed in all of the four HCC cell lines and the tumor specimens from HCC patients. Some other genes were also expressed in them with different level including Nanog, Sox2, STAT3 and TCF3, wnt10b, β-catenin, ELF, Smad3 and Smad4. The ability of the clone formation and migration of the HepG2 decreased after Oct4 was knockdowned. Silencing of Oct4 and TCF3 in HCC cell line HepG2 revealed that there were complicated relationships among Oct4, wnt/β-catenin family and TGF-β family genes. Knockdowning Oct4 reduced the expression of TGF-β family genes ELF, Smad3, Smad4 and wnt/β-catenin family genes, wnt10b, and β-catenin but increased TCF3. In reverse, knockdowning TCF3 led to the increased expression of Oct4 and TGF-β family genes. In conclusion, the expression of Oct4 in HCC may play an important role as in stem cell. Because Oct4 improves not only the function of wnt/β-catenin, but also the TGF-β signal pathways, the significance of its expression in HCC might be more complicated than we evinced before.     

TRAF4 mediates activation of TGF-β signaling and is a biomarker for oncogenesis in breast cancer

The tumor-promoting arm of transforming growth factor beta(TGF-β)receptor signaling contributes to advanced cancer progression and is considered a master regulator of breast cancer metastasis.In mammals,there are six distinct members in the tumor-necrosis factor receptor(TNFR)-associated factor(TRAF)family(TRAF1–TRAF6),with the function of TRAF4 not being extensively studied in the past decade.Although numerous studies have suggested that there is elevated TRAF4 expression in human cancer,it is still unknown in which oncogenic pathway TRAF4 is mainly implicated.This review highlights TGF-β-induced SMAD-dependent signaling and non-SMAD signaling as the major pathways regulated by TRAF4 involved in breast cancer metastasis.     

Emergence, development and diversification of the TGF- β signalling pathway within the animal kingdom

Background  

The question of how genomic processes, such as gene duplication, give rise to co-ordinated organismal properties, such as emergence of new body plans, organs and lifestyles, is of importance in developmental and evolutionary biology. Herein, we focus on the diversification of the transforming growth factor- β (TGF- β) pathway – one of the fundamental and versatile metazoan signal transduction engines.     

Loss of TGF-β responsiveness in prostate stromal cells alters chemokine levels and facilitates the development of mixed osteoblastic/osteolytic bone lesions

Loss of TGF-β type II receptor (TβRII, encoded by Tgfbr2) expression in the prostate stroma contributes to prostate cancer initiation, progression, and invasion. We evaluated whether TβRII loss also affected prostate cancer bone metastatic growth. Immunohistologic analysis revealed that TβRII expression was lost in cancer-associated fibroblasts in human prostate cancer bone metastatic tissues. We recapitulated the human situation with a conditional stromal Tgfbr2 knockout (Tgfbr2-KO) mouse model. Conditioned media from primary cultured Tgfbr2-KO or control Tgfbr2-flox prostatic fibroblasts (koPFCM or wtPFCM, respectively) were applied to C4-2B prostate cancer cells before grafting the cells tibially. We found that koPFCM promoted prostate cancer cell growth in the bone and development of early mixed osteoblastic/osteolytic bone lesions. Furthermore, the koPFCM promoted greater C4-2B adhesion to type-I collagen, the major component of bone matrix, compared to wtPFCM-treated C4-2B. Cytokine antibody array analysis revealed that koPFCM had more than two-fold elevation in granulocyte colony-stimulating factor and CXCL1, CXCL16, and CXCL5 expression relative to wtPFCM. Interestingly, neutralizing antibodies of CXCL16 or CXCL1 were able to reduce koPFCM-associated C4-2B type-I collagen adhesion to that comparable with wtPFCM-mediated adhesion. Collectively, our data indicate that loss of TGF-β responsiveness in prostatic fibroblasts results in upregulation of CXCL16 and CXCL1 and that these paracrine signals increase prostate cancer cell adhesion in the bone matrix. These microenvironment changes at the primary tumor site can mediate early establishment of prostate cancer cells in the bone and support subsequent tumor development at the metastatic site.     

TGFβ signalling in the development of ovarian function

Ovarian development begins back in the embryo with the formation of primordial germ cells and their subsequent migration and colonisation of the genital ridges. Once the ovary has been defined structurally, the primordial germ cells transform into oocytes and become housed in structures called follicles (in this case, primordial follicles), a procedure that, in most mammals, occurs either shortly before or during the first few days after birth. The growth and differentiation of follicles from the primordial population is termed folliculogenesis. Primordial follicles give rise to primary follicles that transform into preantral follicles, then antral follicles (secondary follicles) and, finally (preovulatory) Graafian follicles (tertiary follicles) in a co-ordinated series of transitions regulated by hormones and local intraovarian factors. Members of the transforming growth factor-β (TGFβ) superfamily have been shown to play important roles in this developmental process starting with the specification of primordial germ cells by the bone morphogenetic proteins through to the recruitment of primordial follicles by anti-Mullerian hormone and, potentially, growth and differentiation factor-9 (GDF9) and, finally, their transformation into preantral and antral follicles in response to activin and TGF-β. Developmental and mutant mouse models have been used to show the importance of this family of growth factors in establishing the first wave of folliculogenesis.The author thanks the NHMRC of Australia for funding (Regkey 241000).     

TMEPAI inhibits TGF-β signaling by promoting lysosome degradation of TGF-β receptor and contributes to lung cancer development

Transforming growth factor-β (TGF-β) signaling plays important roles in embryogenesis and tumorigenesis by controlling cell growth, differentiation and migration. The transmembrane prostate androgen-induced protein (TMEPAI) is elevated in several cancers. TMEPAI expression is induced by TGF-β signaling, and in turn, expression of TMEPAI negatively regulates TGF-β signaling, but the molecular mechanisms of TMEPAI induced TGF-β signaling inhibition are not well understood. Here we report that TMEPAI is localized to the lysosome and late endosome, and that association of TMEPAI with the E3 ubiquitin ligase Nedd4 is required for its transport to the lysosome. TMEPAI associates with the TGF-β type I receptor (TβRI) and promotes its degradation in the lysosome. Depletion of TMEPAI in A549 lung cancer cells inhibits cell proliferation, migration and invasion, while TMEPAI expression in nude mice promotes tumorigenesis. These results reveal a novel function for TMEPAI in regulating TGF-β signaling through the modulation of TβRI levels, which has important implications for cancer development in vivo.     

Role of TGF-β signaling in the mechanisms of tamoxifen resistance

The transforming growth factor beta (TGF-β) signaling pathway plays complex role in the regulation of cell proliferation, apoptosis and differentiation in breast cancer. TGF-β activation can lead to multiple cellular responses mediating the drug resistance evolution, including the resistance to antiestrogens. Tamoxifen is the most commonly prescribed antiestrogen that functionally involved in regulation of TGF-β activity. In this review, we focus on the role of TGF-β signaling in the mechanisms of tamoxifen resistance, including its interaction with estrogen receptors alfa (ERα) pathway and breast cancer stem cells (BCSCs). We summarize the current reported data regarding TGF-β signaling components as markers of tamoxifen resistance and review current approaches to overcoming tamoxifen resistance based on studies of TGF-β signaling.     

Pathogenic role of TGF-β in the progression of podocyte diseases

In patients with progressive podocyte diseases, such as focal segmental glomerulosclerosis and membranous nephropathy, there is enhanced expression of transforming growth factor (TGF-β) in podocytes. Biomechanical strain in these diseases may cause overexpression of TGF-β and angiotensin II (Ang II) by podocytes. Oxidative stress induced by Ang II may activate the latent TGF-β. Increased TGF-β activity by podocytes may induce not only the thickening of the glomerular basement membrane (GBM), but also podocyte apoptosis and/or detachment from the GBM, initiating the development of glomerulosclerosis. Furthermore, mesangial matrix expansion frequently occurs in podocyte diseases in association with the development of glomerulosclerosis. This review examines open questions on the pathogenic role of TGF-β that links podocyte injury to GBM thickening, podocyte loss, mesangial matrix expansion and glomerulosclerosis in podocyte diseases. It also describes paracrine regulatory mechanisms of podocyte TGF-β on mesangial cells leading to increased matrix synthesis.