The PIAS3-Smurf2 sumoylation pathway suppresses breast cancer organoid invasiveness

AMPK induces PIAS3 mediated SUMOylation of E3 ubiquitin ligase Smurf1 impairing osteogenic differentiation and traumatic heterotopic ossification

AMP-activated protein kinase (AMPK) is a typical sensor of intracellular energy metabolism. Our previous study revealed the role of activated AMPK in the suppression of osteogenic differentiation and traumatic heterotopic ossification, but the underlying mechanism remains poorly understood. The E3 ubiquitin ligase Smurf1 is a crucial regulator of osteogenic differentiation and bone formation. We report here that Smurf1 is primarily SUMOylated at a C-terminal lysine residue (K324), which enhances its activity, facilitating ALK2 proteolysis and subsequent bone morphogenetic protein (BMP) signaling pathway inhibition. Furthermore, SUMOylation of the SUMO E3 ligase PIAS3 and Smurf1 SUMOylation was suppressed during the osteogenic differentiation and traumatic heterotopic ossification. More importantly, we found that AMPK activation enhances the SUMOylation of Smurf1, which is mediated by PIAS3 and increases the association between PIAS3 and AMPK. Overall, our study revealed that Smurf1 can be SUMOylated by PIAS3, Furthermore, Smurf1 SUMOylation mediates osteogenic differentiation and traumatic heterotopic ossification through suppression of the BMP signaling pathway. This study revealed that promotion of Smurf1 SUMOylation by AMPK activation may be implicated in traumatic heterotopic ossification treatment.

In Vitro Organoid-Based Assays Reveal SMAD4 Tumor-Suppressive Mechanisms for Serrated Colorectal Cancer Invasion

Colon cancer is the third most prominent cancer and second leading cause of cancer-related deaths in the United States. Up to 20% of colon cancers follow the serrated tumor pathway driven by mutations in the MAPK pathway. Loss of SMAD4 function occurs in the majority of late-stage colon cancers and is associated with aggressive cancer progression. Therefore, it is important to develop technology to accurately model and better understand the genetic mechanisms behind cancer invasion. Organoids derived from tumors found in the Smad4KO BRAFV600E/+ mouse model present multiple phenotypes characteristic of invasion both in ex vivo and in vivo systems. Smad4KO BRAFV600E/+ tumor organoids can migrate through 3D culture and infiltrate through transwell membranes. This invasive behavior can be suppressed when SMAD4 is re-expressed in the tumor organoids. RNA-Seq analysis reveals that SMAD4 expression in organoids rapidly regulates transcripts associated with extracellular matrix and secreted proteins, suggesting that the mechanisms employed by SMAD4 to inhibit invasion are associated with regulation of extracellular matrix and secretory pathways. These findings indicate new models to study SMAD4 regulation of tumor invasion and an additional layer of complexity in the tumor-suppressive function of the SMAD4/Tgfβ pathway.

The SUMOylation and ubiquitination crosstalk in cancer

BACKGROUND

The cancer occurrence and progression are largely affected by the post-translational modifications (PTMs) of proteins. Currently, it has been shown that the relationship between ubiquitination and SUMOylation is highly complex and interactive. SUMOylation affects the process of ubiquitination and degradation of substrates. Contrarily, SUMOylation-related proteins are also regulated by the ubiquitination process thus altering their protein levels or activity. Emerging evidence suggests that the abnormal regulation between this crosstalk may lead to tumorigenesis.

PURPOSE

In this review, we have discussed the study of the relationship between ubiquitination and SUMOylation, as well as the possibility of a corresponding application in tumor therapy.

METHODS

The relevant literatures from PubMed have been reviewed for this article.

CONCLUSION

The interaction between ubiquitination and SUMOylation is crucial for the occurrence and development of cancer. A greater understanding of the crosstalk of SUMOylation and ubiquitination may be more conducive to the development of more selective and effective SUMOylation inhibitors, as well as a promotion of synergy with other tumor treatment strategies.

Sumoylated SnoN interacts with HDAC1 and p300/CBP to regulate EMT-associated phenotypes in mammary organoids

Protein post-translational modification by the small ubiquitin-like modifier (SUMO) regulates the stability, subcellular localization, and interactions of protein substrates with consequences on cellular responses including epithelial-mesenchymal transition (EMT). Transforming growth factor beta (TGFβ) is a potent inducer of EMT with implications for cancer invasion and metastasis. The transcriptional coregulator SnoN suppresses TGFβ-induced EMT-associated responses in a sumoylation-dependent manner, but the underlying mechanisms have remained largely unknown. Here, we find that sumoylation promotes the interaction of SnoN with the epigenetic regulators histone deacetylase 1 (HDAC1) and histone acetylase p300 in epithelial cells. In gain and loss of function studies, HDAC1 suppresses, whereas p300 promotes, TGFβ-induced morphogenetic changes associated with EMT-related events in three-dimensional multicellular organoids derived from mammary epithelial cells or carcinomas. These findings suggest that sumoylated SnoN acts via the regulation of histone acetylation to modulate EMT-related effects in breast cell organoids. Our study may facilitate the discovery of new biomarkers and therapeutics in breast cancer and other epithelial cell-derived cancers.

Single-Cell and Spatial Analysis of Emergent Organoid Platforms

Organoids have emerged as a promising advancement of the two-dimensional (2D) culture systems to improve studies in organogenesis, drug discovery, precision medicine, and regenerative medicine applications. Organoids can self-organize as three-dimensional (3D) tissues derived from stem cells and patient tissues to resemble organs. This chapter presents growth strategies, molecular screening methods, and emerging issues of the organoid platforms. Single-cell and spatial analysis resolve organoid heterogeneity to obtain information about the structural and molecular cellular states. Culture media diversity and varying lab-to-lab practices have resulted in organoid-to-organoid variability in morphology and cell compositions. An essential resource is an organoid atlas that can catalog protocols and standardize data analysis for different organoid types. Molecular profiling of individual cells in organoids and data organization of the organoid landscape will impact biomedical applications from basic science to translational use.

Cancer-Associated Dysregulation of Sumo Regulators: Proteases and Ligases

SUMOylation is a post-translational modification that has emerged in recent decades as a mechanism involved in controlling diverse physiological processes and that is essential in vertebrates. The SUMO pathway is regulated by several enzymes, proteases and ligases being the main actors involved in the control of sumoylation of specific targets. Dysregulation of the expression, localization and function of these enzymes produces physiological changes that can lead to the appearance of different types of cancer, depending on the enzymes and target proteins involved. Among the most studied proteases and ligases, those of the SENP and PIAS families stand out, respectively. While the proteases involved in this pathway have specific SUMO activity, the ligases may have additional functions unrelated to sumoylation, which makes it more difficult to study their SUMO-associated role in cancer process. In this review we update the knowledge and advances in relation to the impact of dysregulation of SUMO proteases and ligases in cancer initiation and progression.

3D and organoid culture in research: physiology, hereditary genetic diseases and cancer

In nature, cells reside in tissues subject to complex cell–cell interactions, signals from extracellular molecules and niche soluble and mechanical signaling. These microenvironment interactions are responsible for cellular phenotypes and functions, especially in normal settings. However, in 2D cultures, where interactions are limited to the horizontal plane, cells are exposed uniformly to factors or drugs; therefore, this model does not reconstitute the interactions of a natural microenvironment. 3D culture systems more closely resemble the architectural and functional properties of in vivo tissues. In these 3D cultures, the cells are exposed to different concentrations of nutrients, growth factors, oxygen or cytotoxic agents depending on their localization and communication. The 3D architecture also differentially alters the physiological, biochemical, and biomechanical properties that can affect cell growth, cell survival, differentiation and morphogenesis, cell migration and EMT properties, mechanical responses and therapy resistance. This latter point may, in part, explain the failure of current therapies and affect drug discovery research. Organoids are a promising 3D culture system between 2D cultures and in vivo models that allow the manipulation of signaling pathways and genome editing of cells in a body-like environment but lack the many disadvantages of a living system. In this review, we will focus on the role of stem cells in the establishment of organoids and the possible therapeutic applications of this model, especially in the field of cancer research.

The Role of SUMO E3 Ligases in Signaling Pathway of Cancer Cells

Small ubiquitin-like modifier (SUMO)ylation is a reversible post-translational modification that plays a crucial role in numerous aspects of cell physiology, including cell cycle regulation, DNA damage repair, and protein trafficking and turnover, which are of importance for cell homeostasis. Mechanistically, SUMOylation is a sequential multi-enzymatic process where SUMO E3 ligases recruit substrates and accelerate the transfer of SUMO onto targets, modulating their interactions, localization, activity, or stability. Accumulating evidence highlights the critical role of dysregulated SUMO E3 ligases in processes associated with the occurrence and development of cancers. In the present review, we summarize the SUMO E3 ligases, in particular, the novel ones recently identified, and discuss their regulatory roles in cancer pathogenesis.

Therapeutic Potential of Targeting the SUMO Pathway in Cancer

SUMOylation is a dynamic and reversible post-translational modification, characterized more than 20 years ago, that regulates protein function at multiple levels. Key oncoproteins and tumor suppressors are SUMO substrates. In addition to alterations in SUMO pathway activity due to conditions typically present in cancer, such as hypoxia, the SUMO machinery components are deregulated at the genomic level in cancer. The delicate balance between SUMOylation and deSUMOylation is regulated by SENP enzymes possessing SUMO-deconjugation activity. Dysregulation of SUMO machinery components can disrupt the balance of SUMOylation, contributing to the tumorigenesis and drug resistance of various cancers in a context-dependent manner. Many molecular mechanisms relevant to the pathogenesis of specific cancers involve SUMO, highlighting the potential relevance of SUMO machinery components as therapeutic targets. Recent advances in the development of inhibitors targeting SUMOylation and deSUMOylation permit evaluation of the therapeutic potential of targeting the SUMO pathway in cancer. Finally, the first drug inhibiting SUMO pathway, TAK-981, is currently also being evaluated in clinical trials in cancer patients. Intriguingly, the inhibition of SUMOylation may also have the potential to activate the anti-tumor immune response. Here, we comprehensively and systematically review the recent developments in understanding the role of SUMOylation in cancer and specifically focus on elaborating the scientific rationale of targeting the SUMO pathway in different cancers.

SUMOylation Wrestles With the Occurrence and Development of Breast Cancer

Breast cancer has the highest incidence among cancers and is the most frequent cause of death in women worldwide. The detailed mechanism of the pathogenesis of breast cancer has not been fully elucidated, and there remains a lack of effective treatment methods for the disease. SUMOylation covalently conjugates a large amount of cellular proteins, and affects their cellular localization and biological activity to participate in numerous cellular processes. SUMOylation is an important process and imbalance of SUMOylation results in the progression of human diseases. Increasing evidence shows that numerous SUMOylated proteins are involved in the occurrence and development of breast cancer. This review summarizes a series of studies on protein SUMOylation in breast cancer in recent years. The study of SUMOylated proteins provides a comprehensive understanding of the pathophysiology of breast cancer and provides evolving therapeutic strategies for the treatment of breast cancer.

Posttranslational Modifications of Smurfs: Emerging Regulation in Cancer

Smad ubiquitination regulatory factors (Smurfs) belong to the Nedd4 subfamily of HECT-type E3 ubiquitin ligases. Under normal situations, Smurfs are exactly managed by upstream regulators, and thereby strictly control tumor biological processes, including cell growth, differentiation, apoptosis, polarization, epithelial mesenchymal transition (EMT), and invasion. Disruption of Smurf activity has been implicated in cancer progression, and Smurf activity is controlled by a series of posttranslational modifications (PTMs), including phosphorylation, ubiquitination, neddylation, sumoylation, and methylation. The effect and function of Smurfs depend on PTMs and regulate biological processes. Specifically, these modifications regulate the functional expression of Smurfs by affecting protein degradation and protein interactions. In this review, we summarize the complexity and diversity of Smurf PTMs from biochemical and biological perspectives and highlight the understanding of their roles in cancer.

Regulation of epithelial-mesenchymal transition and organoid morphogenesis by a novel TGFβ-TCF7L2 isoform-specific signaling pathway

Alternative splicing contributes to diversification of gene function, yet consequences of splicing on functions of specific gene products is poorly understood. The major transcription factor TCF7L2 undergoes alternative splicing but the biological significance of TCF7L2 isoforms has remained largely to be elucidated. Here, we find that the TCF7L2 E-isoforms maintain, whereas the M and S isoforms disrupt morphogenesis of 3D-epithelial cell-derived organoids via regulation of epithelial-mesenchymal transition (EMT). Remarkably, TCF7L2E2 antagonizes, whereas TCF7L2M2/S2 promotes EMT-like effects in epithelial cells induced by transforming growth factor beta (TGFβ) signaling. In addition, we find TGFβ signaling reduces the proportion of TCF7L2E to TCF7L2M/S protein in cells undergoing EMT. We also find that TCF7L2 operates via TGFβ-Smad3 signaling to regulate EMT. Collectively, our findings unveil novel isoform-specific functions for the major transcription factor TCF7L2 and provide novel links between TCF7L2 and TGFβ signaling in the control of EMT-like responses and epithelial tissue morphogenesis.

PIAS1 and TIF1γ collaborate to promote SnoN SUMOylation and suppression of epithelial-mesenchymal transition

SUMO E3 ligases specify protein substrates for SUMOylation. The SUMO E3 ligases PIAS1 and TIF1γ target the transcriptional regulator SnoN for SUMOylation leading to suppression of epithelial-mesenchymal transition (EMT). Whether and how TIF1γ and PIAS1 might coordinate SnoN SUMOylation and regulation of EMT remained unknown. Here, we reveal that SnoN associates simultaneously with both TIF1γ and PIAS1, leading to a trimeric protein complex. Hence, PIAS1 and TIF1γ collaborate to promote the SUMOylation of SnoN. Importantly, loss of function studies of PIAS1 and TIF1γ suggest that these E3 ligases act in an interdependent manner to suppress EMT of breast cell-derived tissue organoids. Collectively, our findings unveil a novel mechanism by which SUMO E3 ligases coordinate substrate SUMOylation with biological implications.

The Post-translational Modifications of Smurf2 in TGF-β Signaling

Smad ubiquitin regulatory factor 2 (Smurf2), an essential negative regulator of TGF-β signaling, ubiquitinates TGF-β receptors (TβRs) and Smad proteins, inducing their proteasomal degradation. Smurf2 plays crucial roles in regulating TGF-β signaling and maintaining normal cellular functions and tissue homeostasis; dysfunction of Smurf2 triggers abnormal TGF-β signaling in pathological states. Smurf2 has been reported as a potentially strong candidate for targeting therapies for related diseases. Recent work has begun to focus on the regulation of Smurf2 itself, and emerging evidence indicates that Smurf2 is regulated by post-translational modifications (PTMs) mechanisms. These mechanisms predominantly regulate the expression level and E3 ligase activity of Smurf2, strongly suggesting that this protein contributes to complicated roles under multiple pathophysiological conditions. In this review, we cover some significant and novel mechanisms of the PTMs that potentially control Smurf2 participation in TGF-β signaling, including ubiquitylation, SUMOylation, neddylation, phosphorylation, and methylation in order to provide a broad view of the depth and sophistication of Smurf2 function in TGF-β regulation, as well as perspectives for future therapeutic directions for its associated diseases.

ROR2 suppresses metastasis of prostate cancer via regulation of miR-199a-5p-PIAS3-AKT2 signaling axis

Bones are the most common metastatic sites for prostate cancer (PCa). Receptor tyrosine kinase-like orphan receptor 2 (ROR2), a noncanonical Wnt receptor, plays crucial roles in skeletal morphogenesis, osteoblast differentiation, and bone formation. The role of ROR2 in PCa metastasis is unclear. We analyzed online datasets from Oncomine as well as using IHC staining on tissue array to determine the relationship between ROR2 expression level and disease outcome of PCa. To investigate how ROR2 regulates migration and invasion of PCa cells, we performed transwell assay and orthotopic xenograft model in nude mice. We then applied the Micro-Western Array (MWA), a high-throughput western blotting platform to analyze the downstream signaling pathways being regulated by ROR2. Compared with nonmalignant PZ-HPV-7 and RWPE-1 cells, PCa cell lines express lower level of ROR2 protein. Constitutive expression of ROR2 in PC-3, DU-145, or C4-2B PCa cells significantly suppressed the cell migration, invasion, and epithelial-mesenchymal transition (EMT) proteins. MWA, western blotting, and microRNA analysis showed that elevation of ROR2 suppressed the expression of miR-199a-5p, which in turn increased the expression of PIAS3. The upregulation of PIAS3 then decreased AKT2 and the phosphorylation of AKT, resulting in the inhibition of migration and invasion of PCa cells both in vitro and in orthotopic xenograft mice model. IHC staining of tissue array and Oncomine datasets analysis indicated that the gene and protein level of ROR2 is much lower in metastatic prostate tumors as compared with primary tumors or adjacent normal prostate tissues. Low level of ROR2 correlated to poor survival and high recurrent frequency in PCa patients. In conclusion, we discovered that ROR2 suppresses PCa metastasis via regulation of PIAS3-PI3K-AKT2 signaling axis.

Progress in the application of organoids to breast cancer research

Breast cancer is the most common cancer diagnosed in women. Breast cancer research is currently based mainly on animal models and traditional cell culture. However, the inherent species gap between humans and animals, as well as differences in organization between organs and cells, limits research advances. The breast cancer organoid can reproduce many of the key features of human breast cancer, thereby providing a new platform for investigating the mechanisms underlying the development, progression, metastasis and drug resistance of breast cancer. The application of organoid technology can also promote drug discovery and the design of individualized treatment strategies. Here, we discuss the latest advances in the use of organoid technology for breast cancer research.

The implication of the SUMOylation pathway in breast cancer pathogenesis and treatment

Breast cancer is the most commonly diagnosed malignancy in woman worldwide, and is the second most common cause of death in developed countries. The transformation of a normal cell into a malignant derivate requires the acquisition of diverse genomic and proteomic changes, including enzymatic post-translational modifications (PTMs) on key proteins encompassing critical cell signaling events. PTMs occur on proteins after translation, and regulate several aspects of proteins activity, including their localization, activation and turnover. Deregulation of PTMs can potentially lead to tumorigenesis, and several de-regulated PTM pathways contribute to abnormal cell proliferation during breast tumorigenesis. SUMOylation is a PTM that plays a pivotal role in numerous aspects of cell physiology, including cell cycle regulation, protein trafficking and turnover, and DNA damage repair. Consistently with this, the deregulation of the SUMO pathway is observed in different human pathologies, including breast cancer. In this review we will describe the role of SUMOylation in breast tumorigenesis and its implication for breast cancer therapy.

Ubiquitin, SUMO, and Nedd8 as Therapeutic Targets in Cancer

Ubiquitin defines a family of approximately 20 peptidic posttranslational modifiers collectively called the Ubiquitin-like (UbLs). They are conjugated to thousands of proteins, modifying their function and fate in many ways. Dysregulation of these modifications has been implicated in a variety of pathologies, in particular cancer. Ubiquitin, SUMO (-1 to -3), and Nedd8 are the best-characterized UbLs. They have been involved in the regulation of the activity and/or the stability of diverse components of various oncogenic or tumor suppressor pathways. Moreover, the dysregulation of enzymes responsible for their conjugation/deconjugation has also been associated with tumorigenesis and cancer resistance to therapies. The UbL system therefore constitutes an attractive target for developing novel anticancer therapeutic strategies. Here, we review the roles and dysregulations of Ubiquitin, SUMO, and Nedd8 pathways in tumorigenesis, as well as recent advances in the identification of small molecules targeting their conjugating machineries for potential application in the fight against cancer.

The functions and regulation of Smurfs in cancers

Smad ubiquitination regulatory factor 1 (Smurf1) and Smurf2 are HECT-type E3 ubiquitin ligases, and both Smurfs were initially identified to regulate Smad protein stability in the TGF-β/BMP signaling pathway. In recent years, Smurfs have exhibited E3 ligase-dependent and -independent activities in various kinds of cells. Smurfs act as either potent tumor promoters or tumor suppressors in different tumors by regulating biological processes, including metastasis, apoptosis, cell cycle, senescence and genomic stability. The regulation of Smurfs activity and expression has therefore emerged as a hot spot in tumor biology research. Further, the Smurf1- or Smurf2-deficient mice provide more in vivo clues for the functional study of Smurfs in tumorigenesis and development. In this review, we summarize these milestone findings and, in turn, reveal new avenues for the prevention and treatment of cancer by regulating Smurfs.

Emerging organoid models: leaping forward in cancer research

Cancer heterogeneity is regarded as the main reason for the failure of conventional cancer therapy. The ability to reconstruct intra- and interpatient heterogeneity in cancer models is crucial for understanding cancer biology as well as for developing personalized anti-cancer therapy. Cancer organoids represent an emerging approach for creating patient-derived in vitro cancer models that closely recapitulate the pathophysiological features of natural tumorigenesis and metastasis. Meanwhile, cancer organoids have recently been utilized in the discovery of personalized anti-cancer therapy and prognostic biomarkers. Further, the synergistic combination of cancer organoids with organ-on-a-chip and 3D bioprinting presents a new avenue in the development of more sophisticated and optimized model systems to recapitulate complex cancer-stroma or multiorgan metastasis. Here, we summarize the recent advances in cancer organoids from a perspective of the in vitro emulation of natural cancer evolution and the applications in personalized cancer theranostics. We also discuss the challenges and trends in reconstructing more comprehensive cancer models for basic and clinical cancer research.

The role of protein inhibitor of activated STAT3 and miRNA-18a expressions in breast cancer

Background

Breast cancer is a disease characterized by progressive genetic abnormalities including mutations in tumor suppressor genes and oncogenes, as well as other chromosomal abnormalities. Protein inhibitor of activated signal transducer and activator of transcription 3 (PIAS3) is a member of the PIAS family of transcriptional modulators; its expression is altered in many cancers. Micro-ribonucleic acid (miRNA)-18a acts as an oncogene by negatively regulating PIAS3 and thus modulating the expression of signal transducer and activator of transcription 3 (STAT3) target genes. The aim of this work is to examine the expression levels of PIAS3 gene and miRNA-18a in breast cancer tissues and nearby non-tumor tissues. The samples of breast cancer and paired samples of non-cancerous tissue from the same resected breast were obtained from 25 patients undergoing surgery. Full history taking, complete physical examination, pre-operative fine-needle aspiration cytology or ultrasonic (U/S)-guided core biopsy from the breast mass, final surgical biopsy for pathological examination, and routine laboratory investigations were done. Estrogen receptors (ER), progesterone receptors (PR), and human epidermal growth factor receptor 2 (HER2) status were evaluated. Total RNA extraction followed by real-time reverse transcription-polymerase chain reaction (RT-PCR) for quantification of PIAS3 mRNA and miRNA-18a expressions was performed.

Results

The mean value of PIAS3 mRNA fold expression was significantly lower in the tumor group (5.12 ± 9.85) compared to the normal group (8.38 ± 17.10) (p = 0.040). miRNA-18a fold expression was higher among tumor group (3.5 ± 7.4) than that of normal group (2.5 ± 3), however, it did not reach the level of statistical significance (p = 0.861). miRNA-18a fold expression had negative significant correlation with PIAS3 mRNA fold expression (p = 0.018). A significant association was observed between miRNA-18a expression in breast cancer tissues and the pathological grade of the tumor (p = 0.029).

Conclusions

The results of this study showed that PIAS3 mRNA and miRNA-18a might be of importance in breast cancer development and pathogenesis, and this may be reflected on the treatment strategies targeting STAT3 pathway. However, further studies with larger sample size are needed to validate these observations.

Protein inhibitor of activated STAT genes are differentially expressed in breast tumor tissues

Aim: Protein inhibitor of activated STAT ( PIAS) family includes transcriptional regulator proteins with SUMO E3 ligase activity. They regulate expression of several genes involved in cell proliferation, differentiation and survival. Method: We evaluated expression of PIAS1–4 genes in 54 breast cancer tissues and their paired adjacent noncancerous tissues. Results: PIAS2 and PIAS3 genes were significantly downregulated in tumoral tissues compared with adjacent noncancerous tissues. PIAS1–3 expressions were significantly lower in estrogen receptor (ER+) samples compared with ER- samples while PIAS4 had the opposite trend. PIAS3 expression was significantly higher in grade 1 samples compared with grade 2 samples. Conclusion: These findings highlight the role of PIAS genes in the pathogenesis of breast cancer and their association with determinants of response to antihormone therapies.

NEDD4 Family of E3 Ubiquitin Ligases in Breast Cancer: Spotlight on SMURFs, WWPs and NEDD4

Massively parallel sequencing, genomic and proteomic technologies have provided near complete resolution of signaling landscape of breast cancer (BCa). NEDD4 family of E3-ubiquitin ligases comprises a large family of proteins particularly, SMURFs (SMURF1, SMURF2), WWPs and NEDD4 which are ideal candidates for targeted therapy. However, it is becoming progressively more understandable that SMURFs and NEDD4 have "split-personalities". These molecules behave dualistically in breast cancer and future studies must converge on detailed identification of context specific role of these proteins in BCa. Finally, we provide scattered clues of regulation of SMURF2 by oncogenic miRNAs, specifically considering longstanding questions related to regulation of SMURF1 and WWPs by miRNAs in BCa. SMURFS, WWPs and NEDD4 are versatile regulators and represent a fast-growing field in cancer research and better understanding of the underlying mechanisms will be helpful in transition of our knowledge from a segmented view to a more conceptual continuum.

WW-Domain Containing Protein Roles in Breast Tumorigenesis

Protein-protein interactions are key factors in executing protein function. These interactions are mediated through different protein domains or modules. An important domain found in many different types of proteins is WW domain. WW domain-containing proteins were shown to be involved in many human diseases including cancer. Some of these proteins function as either tumor suppressor genes or oncogenes, while others show dual identity. Some of these proteins act on their own and alter the function(s) of specific or multiple proteins implicated in cancer, others interact with their partners to compose WW domain modular pathway. In this review, we discuss the role of WW domain-containing proteins in breast tumorigenesis. We give examples of specific WW domain containing proteins that play roles in breast tumorigenesis and explain the mechanisms through which these proteins lead to breast cancer initiation and progression. We discuss also the possibility of using these proteins as biomarkers or therapeutic targets.

Regulating the human HECT E3 ligases

Ubiquitination, the covalent attachment of ubiquitin to proteins, by E3 ligases of the HECT (homologous to E6AP C terminus) family is critical in controlling diverse physiological pathways. Stringent control of HECT E3 ligase activity and substrate specificity is essential for cellular health, whereas deregulation of HECT E3s plays a prominent role in disease. The cell employs a wide variety of regulatory mechanisms to control HECT E3 activity and substrate specificity. Here, we summarize the current understanding of these regulatory mechanisms that control HECT E3 function. Substrate specificity is generally determined by interactions of adaptor proteins with domains in the N-terminal extensions of HECT E3 ligases. These N-terminal domains have also been found to interact with the HECT domain, resulting in the formation of inhibitory conformations. In addition, catalytic activity of the HECT domain is commonly regulated at the level of E2 recruitment and through HECT E3 oligomerization. The previously mentioned regulatory mechanisms can be controlled through protein-protein interactions, post-translational modifications, the binding of calcium ions, and more. Functional activity is determined not only by substrate recruitment and catalytic activity, but also by the type of ubiquitin polymers catalyzed to the substrate. While this is often determined by the specific HECT member, recent studies demonstrate that HECT E3s can be modulated to alter the type of ubiquitin polymers they catalyze. Insight into these diverse regulatory mechanisms that control HECT E3 activity may open up new avenues for therapeutic strategies aimed at inhibition or enhancement of HECT E3 function in disease-related pathways.

The SUMO System and TGFβ Signaling Interplay in Regulation of Epithelial-Mesenchymal Transition: Implications for Cancer Progression

Protein post-translational modification by the small ubiquitin-like modifier (SUMO), or SUMOylation, can regulate the stability, subcellular localization or interactome of a protein substrate with key consequences for cellular processes including the Epithelial-Mesenchymal Transition (EMT). The secreted protein Transforming Growth Factor beta (TGFβ) is a potent inducer of EMT in development and homeostasis. Importantly, the ability of TGFβ to induce EMT has been implicated in promoting cancer invasion and metastasis, resistance to chemo/radio therapy, and maintenance of cancer stem cells. Interestingly, TGFβ-induced EMT and the SUMO system intersect with important implications for cancer formation and progression, and novel therapeutics identification.

Smurfs in Protein Homeostasis, Signaling, and Cancer

Protein ubiquitination is an evolutionary conserved highly-orchestrated enzymatic cascade essential for normal cellular functions and homeostasis maintenance. This pathway relies on a defined set of cellular enzymes, among them, substrate-specific E3 ubiquitin ligases (E3s). These ligases are the most critical players, as they define the spatiotemporal nature of ubiquitination and confer specificity to this cascade. Smurf1 and Smurf2 (Smurfs) are the C2-WW-HECT-domain E3 ubiquitin ligases, which recently emerged as important determinants of pivotal cellular processes. These processes include cell proliferation and differentiation, chromatin organization and dynamics, DNA damage response and genomic integrity maintenance, gene expression, cell stemness, migration, and invasion. All these processes are intimately connected and profoundly altered in cancer. Initially, Smurf proteins were identified as negative regulators of the bone morphogenetic protein (BMP) and the transforming growth factor beta (TGF-β) signaling pathways. However, recent studies have extended the scope of Smurfs' biological functions beyond the BMP/TGF-β signaling regulation. Here, we provide a critical literature overview and updates on the regulatory roles of Smurfs in molecular and cell biology, with an emphasis on cancer. We also highlight the studies demonstrating the impact of Smurf proteins on tumor cell sensitivity to anticancer therapies. Further in-depth analyses of Smurfs' biological functions and influences on molecular pathways could provide novel therapeutic targets and paradigms for cancer diagnosis and treatment.

Nuclear Smad6 promotes gliomagenesis by negatively regulating PIAS3-mediated STAT3 inhibition

To date, the molecular mechanism underlying constitutive signal transducer and activator of transcription 3 (STAT3) activation in gliomas is largely unclear. In this study, we report that Smad6 is overexpressed in nuclei of glioma cells, which correlates with poor patient survival and regulates STAT3 activity via negatively regulating the Protein Inhibitors of Activated STAT3 (PIAS3). Mechanically, Smad6 interacts directly with PIAS3, and this interaction is mediated through the Mad homology 2 (MH2) domain of Smad6 and the Ring domain of PIAS3. Smad6 recruits Smurf1 to facilitate PIAS3 ubiquitination and degradation, which also depends on the MH2 domain and the PY motif of Smad6. Consequently, Smad6 reduces PIAS3-mediated STAT3 inhibition and promotes glioma cell growth and stem-like cell initiation. Moreover, the Smad6 MH2 transducible protein restores PIAS3 expression and subsequently reduces gliomagenesis. Collectively, we conclude that nuclear-Smad6 enhances glioma development by inducing PIAS3 degradation and subsequent STAT3 activity upregulation.

In glioma STAT3 signaling contributes to gliomagenesis. Here, the authors show that Smad6 expression correlates with poor survival and is overexpressed in glioma cells, and regulates STAT3 activity via negatively regulating PIAS3.

Somatic mutations in early onset luminal breast cancer

Breast cancer arising in very young patients may be biologically distinct; however, these tumors have been less well studied. We characterized a group of very young patients (≤ 35 years) for BRCA germline mutation and for somatic mutations in luminal (HER2 negative) breast cancer. Thirteen of 79 unselected very young patients were BRCA1/2 germline mutation carriers. Of the non-BRCA tumors, eight with luminal subtype (HER2 negative) were submitted for whole exome sequencing and integrated with 29 luminal samples from the COSMIC database or previous literature for analysis. We identified C to T single nucleotide variants (SNVs) as the most common base-change. A median of six candidate driver genes was mutated by SNVs in each sample and the most frequently mutated genes were PIK3CA, GATA3, TP53 and MAP2K4. Potential cancer drivers affected in the present non-BRCA tumors include GRHL2, PIK3AP1, CACNA1E, SEMA6D, SMURF2, RSBN1 and MTHFD2. Sixteen out of 37 luminal tumors (43%) harbored SNVs in DNA repair genes, such as ATR, BAP1, ERCC6, FANCD2, FANCL, MLH1, MUTYH, PALB2, POLD1, POLE, RAD9A, RAD51 and TP53, and 54% presented pathogenic mutations (frameshift or nonsense) in at least one gene involved in gene transcription. The differential biology of luminal early-age onset breast cancer needs a deeper genomic investigation.

Breast Organotypic Cancer Models

Breast cancer is the most common cancer type diagnosed in women, it represents a critical public health problem worldwide, with 1,671,149 estimated new cases and nearly 571,000 related deaths. Research on breast cancer has mainly been conducted using two-dimensional (2D) cell cultures and animal models. The usefulness of these models is reflected in the vast knowledge accumulated over the past decades. However, considering that animal models are three-dimensional (3D) in nature, the validity of the studies using 2D cell cultures has recently been questioned. Although animal models are important in cancer research, ethical questions arise about their use and usefulness as there is no clear predictivity of human disease outcome and they are very expensive and take too much time to obtain results. The poor performance or failure of most cancer drugs suggests that preclinical research on cancer has been based on an over-dependence on inadequate animal models. For these reasons, in the last few years development of alternative models has been prioritized to study human breast cancer behavior, while maintaining a 3D microenvironment, and to reduce the number of experiments conducted in animals. One way to achieve this is using organotypic cultures, which are being more frequently explored in cancer research because they mimic tissue architecture in vivo. These characteristics make organotypic cultures a valuable tool in cancer research as an alternative to replace animal models and for predicting risk assessment in humans. This chapter describes the cultures of multicellular spheroids, organoids, 3D bioreactors, and tumor slices, which are the most widely used organotypic models in breast cancer research.