TGF-beta-dependent and -independent roles of STRAP in cancer

Chaperoning the chaperones: Proteomic analysis of the SMN complex reveals conserved and etiologic connections to the proteostasis network

Molecular chaperones and co-chaperones are highly conserved cellular components that perform variety of duties related to the proper three-dimensional folding of the proteome. The web of factors that carries out this essential task is called the proteostasis network (PN). Ribonucleoproteins (RNPs) represent an underexplored area in terms of the connections they make with the PN. The Survival Motor Neuron (SMN) complex is an RNP assembly chaperone and serves as a paradigm for studying how specific small nuclear (sn)RNAs are identified and paired with their client substrate proteins. SMN protein is the eponymous component of a large complex required for the biogenesis of uridine-rich small nuclear ribonucleoproteins (U-snRNPs) and localizes to distinct membraneless organelles in both the nucleus and cytoplasm of animal cells. SMN forms the oligomeric core of this complex, and missense mutations in its YG box self-interaction domain are known to cause Spinal Muscular Atrophy (SMA). The basic framework for understanding how snRNAs are assembled into U-snRNPs is known, the pathways and mechanisms used by cells to regulate their biogenesis are poorly understood. Given the importance of these processes to normal development as well as neurodegenerative disease, we set out to identify and characterize novel SMN binding partners. Here, we carried out affinity purification mass spectrometry (AP-MS) of SMN using stable fly lines exclusively expressing either wildtype or SMA-causing missense alleles. Bioinformatic analyses of the pulldown data, along with comparisons to proximity labeling studies carried out in human cells, revealed conserved connections to at least two other major chaperone systems including heat shock folding chaperones (HSPs) and histone/nucleosome assembly chaperones. Notably, we found that heat shock cognate protein Hsc70-4 and other HspA family members preferentially interacted with SMA-causing alleles of SMN. Hsc70-4 is particularly interesting because its mRNA is aberrantly sequestered by a mutant form of TDP-43 in mouse and Drosophila ALS (Amyotrophic Lateral Sclerosis) disease models. Most important, a missense allele of Hsc70-4 (HspA8 in mammals) was recently identified as a bypass suppressor of the SMA phenotype in mice. Collectively, these findings suggest that chaperone-related dysfunction lies at the etiological root of both ALS and SMA.

A Multi-Omics Approach Revealed Common Dysregulated Pathways in Type One and Type Two Endometrial Cancers

Endometrial cancer (EC) is the most frequent gynecologic cancer in postmenopausal women. Pathogenetic mechanisms that are related to the onset and progression of the disease are largely still unknown. A multi-omics strategy can help identify altered pathways that could be targeted for improving therapeutical approaches. In this study we used a multi-omics approach on four EC cell lines for the identification of common dysregulated pathways in type 1 and 2 ECs. We analyzed proteomics and metabolomics of AN3CA, HEC1A, KLE and ISHIKAWA cell lines by mass spectrometry. The bioinformatic analysis identified 22 common pathways that are in common with both types of EC. In addition, we identified five proteins and 13 metabolites common to both types of EC. Western blotting analysis on 10 patients with type 1 and type 2 EC and 10 endometria samples confirmed the altered abundance of NPEPPS. Our multi-omics analysis identified dysregulated proteins and metabolites involved in EC tumor growth. Further studies are needed to understand the role of these molecules in EC. Our data can shed light on common pathways to better understand the mechanisms involved in the development and growth of EC, especially for the development of new therapies.

Identification of cuproptosis-related subtypes, establishment of a prognostic model and tumor immune landscape in endometrial carcinoma

Cuproptosis, the mechanism of copper-dependent cell death, is distinct from all other known forms of regulated cell death and dependents on mitochondrial respiration. Cuproptosis promises to be a novel treatment, especially for tumors resistant to conventional therapies. We investigated the changes in cuproptosis-related genes (CRGs) in endometrial cancer (EC) cohorts from the merged Gene Expression Omnibus and the Cancer Genome Atlas databases, which could be divided into three distinct CRGclusters. Patients in CRGcluster C would have higher survival probability (P = 0.007), and higher levels of tumor microenvironment (TME) cell infiltration than other CRGclusters. CRG score was calculated via the results of univariate, multivariate cox analysis and least absolute shrinkage and selection operator regression analysis. Patients were divided into two risk subgroups according to the median risk score. Low-risk patients exhibited a more favorable prognosis, higher immunogenicity, and greater immunotherapy efficacy. Besides, CRG scores were strongly correlated to copy number variation, immunophenoscore, tumor mutation load, cancer stem cell index, microsatellite instability, and chemosensitivity. The c-index of our model is 0.702, which is higher than other four published model. The results proved that our model can distinguish EC patients with high-risk and low-risk and accurately predict the prognosis of EC patients. It will provide new ideas for clinical prognosis and precise treatments.

Serine-Threonine Kinase Receptor Associate Protein (STRAP) confers an aggressive phenotype in neuroblastoma via regulation of Focal Adhesion Kinase (FAK)

BACKGROUND

Serine-threonine kinase receptor associated protein (STRAP), a scaffolding protein, is upregulated in many solid tumors. As such, we hypothesized that STRAP may be overexpressed in neuroblastoma tumors and may play a role in neuroblastoma tumor progression.

METHODS

We examined two publicly available neuroblastoma patient databases, GSE49710 (n = 498) and GSE49711 (n = 498), to investigate STRAP expression in human specimens. SK-N-AS and SK-N-BE(2) human neuroblastoma cell lines were stably transfected with STRAP overexpression (OE) plasmid, and their resulting phenotype studied. PamChip® kinomic peptide microarray evaluated the effects of STRAP overexpression on kinase activation.

RESULTS

In human specimens, higher STRAP expression correlated with high-risk disease, unfavorable histology, and decreased overall neuroblastoma patient survival. STRAP OE in neuroblastoma cell lines led to increased proliferation, growth, supported a stem-like phenotype and activated downstream FAK targets. When FAK was targeted with the small molecule FAK inhibitor, PF-573,228, STRAP OE neuroblastoma cells had significantly decreased growth compared to control empty vector cells.

CONCLUSION

Increased STRAP expression in neuroblastoma was associated with unfavorable tumor characteristics. STRAP OE resulted in increased kinomic activity of FAK. These findings suggest that the poorer outcomes in neuroblastoma tumors associated with STRAP overexpression may be secondary to FAK activation.

Serine-threonine Kinase Receptor-Associated Protein is a Critical Mediator of APC Mutation-Induced Intestinal Tumorigenesis Through a Feed-Forward Mechanism

BACKGROUND & AIMS

Inactivation of the Apc gene is a critical early event in the development of sporadic colorectal cancer (CRC). Expression of serine-threonine kinase receptor-associated protein (STRAP) is elevated in CRCs and is associated with poor outcomes. We investigated the role of STRAP in Apc mutation-induced intestinal tumor initiation and progression.

METHODS

We generated Strap intestinal epithelial knockout mice (StrapΔIEC) by crossing mice containing floxed alleles of Strap (Strapfl/fl) with Villin-Cre mice. Then we generated ApcMin/+;Strapfl/fl;Vill-Cre (ApcMin/+;StrapΔIEC) mice for RNA-sequencing analyses to determine the mechanism of function of STRAP. We used human colon cancer cell lines (DLD1, SW480, and HT29) and human and mouse colon tumor-derived organoids for STRAP knockdown and knockout and overexpression experiments.

RESULTS

Strap deficiency extended the average survival of ApcMin/+ mice by 80 days and decreased the formation of intestinal adenomas. Expression profiling revealed that the intestinal stem cell signature, the Wnt/β-catenin signaling, and the MEK/ERK pathway are down-regulated in Strap-deficient adenomas and intestinal organoids. Correlation studies suggest that these STRAP-associated oncogenic signatures are conserved across murine and human colon cancer. STRAP associates with MEK1/2, promotes binding between MEK1/2 and ERK1/2, and subsequently induces the phosphorylation of ERK1/2. STRAP activated Wnt/β-catenin signaling through MEK/ERK-induced phosphorylation of LRP6. STRAP was identified as a target of mutated Apc and Wnt/β-catenin signaling as chromatin immunoprecipitation and luciferase assays revealed putative binding sites of the β-catenin/TCF4 complex on the Strap promoter.

CONCLUSIONS

STRAP is a target of, and is required in, Apc mutation/deletion-induced intestinal tumorigenesis through a novel feed-forward STRAP/MEK-ERK/Wnt-β-catenin/STRAP regulatory axis.

Serine-Threonine Kinase Receptor-Associated Protein (STRAP) Knockout Decreases the Malignant Phenotype in Neuroblastoma Cell Lines

Background: Serine-threonine kinase receptor-associated protein (STRAP) plays an important role in neural development but also in tumor growth. Neuroblastoma, a tumor of neural crest origin, is the most common extracranial solid malignancy of childhood and it continues to carry a poor prognosis. The recent discovery of the role of STRAP in another pediatric solid tumor, osteosarcoma, and the known function of STRAP in neural development, led us to investigate the role of STRAP in neuroblastoma tumorigenesis. Methods: STRAP protein expression was abrogated in two human neuroblastoma cell lines, SK-N-AS and SK-N-BE(2), using transient knockdown with siRNA, stable knockdown with shRNA lentiviral transfection, and CRISPR-Cas9 genetic knockout. STRAP knockdown and knockout cells were examined for phenotypic alterations in vitro and tumor growth in vivo. Results: Cell proliferation, motility, and growth were significantly decreased in STRAP knockout compared to wild-type cells. Indicators of stemness, including mRNA abundance of common stem cell markers Oct4, Nanog, and Nestin, the percentage of cells expressing CD133 on their surface, and the ability to form tumorspheres were significantly decreased in the STRAP KO cells. In vivo, STRAP knockout cells formed tumors less readily than wild-type tumor cells. Conclusion: These novel findings demonstrated that STRAP plays a role in tumorigenesis and maintenance of neuroblastoma stemness.

Oncogenic roles of serine-threonine kinase receptor-associated protein (STRAP) in osteosarcoma

PURPOSE

To validate the presence of serine-threonine kinase receptor-associated Protein (STRAP) in osteosarcoma tissue and to investigate the oncological role of STRAP in osteosarcoma.

METHODS

Expression of STRAP protein in osteosarcoma tissue compared to soft callus (hyperactive bone healing tissue) and in multiple cell lines was examined using western blot analysis. Effects of STRAP silencing on cell proliferation, invasion, migration and re-implantability in chick chorioallantoic membrane (CAM) were observed in osteosarcoma cell lines (MNNG-HOS, 143B, and U2OS).

RESULTS

The result demonstrated that STRAP was highly up-regulated in osteosarcoma tissues compared with the normal physiological bone healing tissue (soft callus). Expression level of STRAP was markedly high in osteosarcoma cell lines with aggressive phenotype. Upon STRAP silencing, invasion and migration, but not proliferative activity, were selectively modulated in high-expression-STRAP cell lines. In addition, STRAP silencing reduced the success rate of tumor implantation and growth of MNNG-HOS cells in CAM model.

CONCLUSIONS

Serine-threonine kinase receptor-associated protein is up-regulated during osteosarcoma progression. The presence of STRAP enhances osteosarcoma cell invasion, migration and re-implantation ability, factors which play a critical role in metastasis. Serine-threonine kinase receptor-associated protein and its related pathway are worthy for further exploration as a novel target for anti-metastasis agents.

Oncogenic STRAP Supports Hepatocellular Carcinoma Growth by Enhancing Wnt/β-Catenin Signaling

Aberrant activation of Wnt/β-catenin signaling plays a key role in the onset and development of hepatocellular carcinomas (HCC), with about half of them acquiring mutations in either CTNNB1 or AXIN1. The serine/threonine kinase receptor-associated protein (STRAP), a scaffold protein, was recently shown to facilitate the aberrant activation of Wnt/β-catenin signaling in colorectal cancers. However, the function of STRAP in HCC remains completely unknown. Here, increased levels of STRAP were observed in human and mouse HCCs. RNA sequencing of STRAP knockout clones generated by gene editing of Huh6 and Huh7 HCC cells revealed a significant reduction in expression of various metabolic and cell-cycle-related transcripts, in line with their general slower growth observed during culture. Importantly, Wnt/β-catenin signaling was impaired in all STRAP knockout/down cell lines tested, regardless of the underlying CTNNB1 or AXIN1 mutation. In accordance with β-catenin's role in (cancer) stem cell maintenance, the expressions of various stem cell markers, such as AXIN2 and LGR5, were reduced and concomitantly differentiation-associated genes were increased. Together, these results show that the increased STRAP protein levels observed in HCC provide growth advantage among others by enhancing Wnt/β-catenin signaling. These observations also identify STRAP as a new player in regulating β-catenin signaling in hepatocellular cancers. IMPLICATIONS: Elevated STRAP levels in hepatocellular cancers provide a growth advantage by enhancing Wnt/β-catenin signaling.

Dual Roles of Serine-Threonine Kinase Receptor-Associated Protein (STRAP) in Redox-Sensitive Signaling Pathways Related to Cancer Development

Serine-threonine kinase receptor-associated protein (STRAP) is a transforming growth factor β (TGF-β) receptor-interacting protein that has been implicated in both cell proliferation and cell death in response to various stresses. However, the precise roles of STRAP in these cellular processes are still unclear. The mechanisms by which STRAP controls both cell proliferation and cell death are now beginning to be unraveled. In addition to its biological roles, this review also focuses on the dual functions of STRAP in cancers displaying redox dysregulation, where it can behave as a tumor suppressor or an oncogene (i.e., it can either inhibit or promote tumor formation), depending on the cellular context. Further studies are needed to define the functions of STRAP and the redox-sensitive intracellular signaling pathways that enhance either cell proliferation or cell death in human cancer tissues, which may help in the development of effective treatments for cancer.

Downregulation of STRAP promotes tumor growth and metastasis in hepatocellular carcinoma via reducing PTEN level

The serine-threonine kinase receptor-associated protein (STRAP) has been implicated in multiple human cancers. However, its expression and function are currently unclear and controversial in different tissue types. In the present study, we report that aberrant downregulation of STRAP in hepatocellular carcinoma (HCC) facilitated tumor cell growth and metastasis in a phosphatase and tensin homologue (PTEN)-dependent manner. Immunohistochemical analysis and quantitative real-time polymerase chain reaction results indicated that STRAP was frequently downregulated in HCC samples. Functionally, knockdown of STRAP by RNA inference in HCC cells promoted proliferation and migration in vitro and tumorigenicity and lung metastasis in vivo. Through detecting the expression of some tumor-related genes using western blot analysis, we found the tumor suppressor PTEN was decreased upon STRAP silencing. Further analyses demonstrated that silenced STRAP led to PTEN protein degradation. Immunohistochemical analysis revealed that STRAP expression was closely associated with PTEN expression in 30 cases of HCC samples. These findings strongly suggest that STRAP plays an inhibitory role in HCC via regulating PTEN expression and could be a potential therapeutic target for this disease. © 2017 IUBMB Life, 70(2):120-128, 2018.

Novel role of STRAP in progression and metastasis of colorectal cancer through Wnt/β-catenin signaling

Serine-Threonine Kinase Receptor-Associated Protein (STRAP) interacts with a variety of proteins and influences a wide range of cellular processes. Aberrant activation of Wnt/β-catenin signaling has been implicated in the development of colorectal cancer (CRC). Here, we show the molecular mechanism by which STRAP induces CRC metastasis by promoting β-catenin signaling through its stabilization. We have genetically engineered a series of murine and human CRC and lung cancer cell lines to investigate the effects of STRAP on cell migration and invasion in vitro, and on tumorigenicity and metastasis in vivo. Downregulation of STRAP inhibits invasion, tumorigenicity, and metastasis of CRC cells. Mechanistically, STRAP binds with GSK-3β and reduces the phosphorylation, ubiquitylation, and degradation of β-catenin through preventing its binding to the destruction complex. This leads to an inhibition of Wnt/β-catenin signaling and reduction in the expression of downstream targets, such as Cyclin D1, matrix metalloproteinases 2 and 9, and ß-TrCP. In human CRC specimens, higher STRAP expression correlates significantly with β-catenin expression with increased nuclear levels (R =0.696, p < .0001, n =128). Together, these results suggest that STRAP increases invasion and metastasis of CRC partly through inhibiting ubiquitin-dependent degradation of β-catenin and promoting Wnt/β-catenin signaling.

The U2AF1S34F mutation induces lineage-specific splicing alterations in myelodysplastic syndromes

Mutations of the splicing factor–encoding gene U2AF1 are frequent in the myelodysplastic syndromes (MDS), a myeloid malignancy, and other cancers. Patients with MDS suffer from peripheral blood cytopenias, including anemia, and an increasing percentage of bone marrow myeloblasts. We studied the impact of the common U2AF1^S34F mutation on cellular function and mRNA splicing in the main cell lineages affected in MDS. We demonstrated that U2AF1^S34F expression in human hematopoietic progenitors impairs erythroid differentiation and skews granulomonocytic differentiation toward granulocytes. RNA sequencing of erythroid and granulomonocytic colonies revealed that U2AF1^S34F induced a higher number of cassette exon splicing events in granulomonocytic cells than in erythroid cells. U2AF1^S34F altered mRNA splicing of many transcripts that were expressed in both cell types in a lineage-specific manner. In hematopoietic progenitors, the introduction of isoform changes identified in the U2AF1^S34F target genes H2AFY, encoding an H2A histone variant, and STRAP, encoding serine/threonine kinase receptor–associated protein, recapitulated phenotypes associated with U2AF1^S34F expression in erythroid and granulomonocytic cells, suggesting a causal link. Furthermore, we showed that isoform modulation of H2AFY and STRAP rescues the erythroid differentiation defect in U2AF1^S34F MDS cells, suggesting that splicing modulators could be used therapeutically. These data have critical implications for understanding MDS phenotypic heterogeneity and support the development of therapies targeting splicing abnormalities.

Increased Hemodynamic Load in Early Embryonic Stages Alters Endocardial to Mesenchymal Transition

Normal blood flow is essential for proper heart formation during embryonic development, as abnormal hemodynamic load (blood pressure and shear stress) results in cardiac defects seen in congenital heart disease. However, the progressive detrimental remodeling processes that relate altered blood flow to cardiac defects remain unclear. Endothelial-mesenchymal cell transition is one of the many complex developmental events involved in transforming the early embryonic outflow tract into the aorta, pulmonary trunk, interventricular septum, and semilunar valves. This study elucidated the effects of increased hemodynamic load on endothelial-mesenchymal transition remodeling of the outflow tract cushions in vivo. Outflow tract banding was used to increase hemodynamic load in the chicken embryo heart between Hamburger and Hamilton stages 18 and 24. Increased hemodynamic load induced increased cell density in outflow tract cushions, fewer cells along the endocardial lining, endocardium junction disruption, and altered periostin expression as measured by confocal microscopy analysis. In addition, 3D focused ion beam scanning electron microscopy analysis determined that a portion of endocardial cells adopted a migratory shape after outflow tract banding that is more irregular, elongated, and with extensive cellular projections compared to normal cells. Proteomic mass-spectrometry analysis quantified altered protein composition after banding that is consistent with a more active stage of endothelial-mesenchymal transition. Outflow tract banding enhances the endothelial-mesenchymal transition phenotype during formation of the outflow tract cushions, suggesting that endothelial-mesenchymal transition is a critical developmental process that when disturbed by altered blood flow gives rise to cardiac malformation and defects.

Serine threonine kinase receptor associated protein regulates early follicle development in the mouse ovary

The molecular mechanisms involved in regulating the development of small, gonadotrophin-independent follicles are poorly understood; however, many studies have highlighted an essential role for TGFB ligands. Canonical TGFB signalling is dependent upon intracellular SMAD proteins that regulate transcription. STRAP has been identified in other tissues as an inhibitor of the TGFB–SMAD signalling pathway. Therefore, in this study we aimed to determine the expression and role of STRAP in the context of early follicle development. Using qPCR, Strap, Smad3 and Smad7 revealed similar expression profiles in immature ovaries from mice aged 4–16 days containing different populations of early growing follicles. STRAP and SMAD2/3 proteins co-localised in granulosa cells of small follicles using immunofluorescence. Using an established culture model, neonatal mouse ovary fragments with a high density of small non-growing follicles were used to examine the effects of Strap knockdown using siRNA and STRAP protein inhibition by immuno-neutralisation. Both interventions caused a reduction in the proportion of small, non-growing follicles and an increase in the proportion and size of growing follicles in comparison to untreated controls, suggesting inhibition of STRAP facilitates follicle activation. Recombinant STRAP protein had no effect on small, non-growing follicles, but increased the mean oocyte size of growing follicles in the neonatal ovary model and also promoted the growth of isolated preantral follicles in vitro. Overall findings indicate STRAP is expressed in the mouse ovary and is capable of regulating development of small follicles in a stage-dependent manner.

Disruption of snRNP biogenesis factors Tgs1 and pICln induces phenotypes that mirror aspects of SMN-Gemins complex perturbation in Drosophila, providing new insights into spinal muscular atrophy

The neuromuscular disorder, spinal muscular atrophy (SMA), results from insufficient levels of the survival motor neuron (SMN) protein. Together with Gemins 2-8 and Unrip, SMN forms the large macromolecular SMN-Gemins complex, which is known to be indispensable for chaperoning the assembly of spliceosomal small nuclear ribonucleoproteins (snRNPs). It remains unclear whether disruption of this function is responsible for the selective neuromuscular degeneration in SMA. In the present study, we first show that loss of wmd, the Drosophila Unrip orthologue, has a negative impact on the motor system. However, due to lack of a functional relationship between wmd/Unrip and Gemin3, it is likely that Unrip joined the SMN-Gemins complex only recently in evolution. Second, we uncover that disruption of either Tgs1 or pICln, two cardinal players in snRNP biogenesis, results in viability and motor phenotypes that closely resemble those previously uncovered on loss of the constituent members of the SMN-Gemins complex. Interestingly, overexpression of both factors leads to motor dysfunction in Drosophila, a situation analogous to that of Gemin2. Toxicity is conserved in the yeast S. pombe where pICln overexpression induces a surplus of Sm proteins in the cytoplasm, indicating that a block in snRNP biogenesis is partly responsible for this phenotype. Importantly, we show a strong functional relationship and a physical interaction between Gemin3 and either Tgs1 or pICln. We propose that snRNP biogenesis is the pathway connecting the SMN-Gemins complex to a functional neuromuscular system, and its disturbance most likely leads to the motor dysfunction that is typical in SMA.

RNA-seq analysis of impact of PNN on gene expression and alternative splicing in corneal epithelial cells

PURPOSE

The specialized corneal epithelium requires differentiated properties, specific for its role at the anterior surface of the eye. Thus, tight maintenance of the differentiated qualities of the corneal epithelial is essential. Pinin (PNN) is an exon junction component (EJC) that has dramatic implications for corneal epithelial cell differentiation and may act as a stabilizer of the corneal epithelial cell phenotype. Our studies revealed that PNN is involved in transcriptional repression complexes and spliceosomal complexes, placing PNN at the fulcrum between chromatin and mRNA splicing. Transcriptome analysis of PNN-knockdown cells revealed clear and reproducible alterations in transcript profiles and splicing patterns of a subset of genes that would significantly impact the epithelial cell phenotype. We further investigated PNN's role in the regulation of gene expression and alternative splicing (AS) in a corneal epithelial context.

METHODS

Human corneal epithelial (HCET) cells that carry the doxycycline-inducible PNN-knockdown shRNA vector were used to perform RNA-seq to determine differential gene expression and differential AS events.

RESULTS

Multiple genes and AS events were identified as differentially expressed between PNN-knockdown and control cells. Genes upregulated by PNN knockdown included a large proportion of genes that are associated with enhanced cell migration and ECM remodeling processes, such as MMPs, ADAMs, HAS2, LAMA3, CXCRs, and UNC5C. Genes downregulated in response to PNN depletion included IGFBP5, FGD3, FGFR2, PAX6, RARG, and SOX10. AS events in PNN-knockdown cells compared to control cells were also more likely to be detected, and upregulated. In particular, 60% of exon-skipping events, detected in only one condition, were detected in PNN-knockdown cells and of the shared exon-skipping events, 92% of those differentially expressed were more frequent in the PNN knockdown.

CONCLUSIONS

These data suggest that lowering of PNN levels in epithelial cells results in dramatic transformation in the number and composition of splicing variants and that PNN plays a crucial role in the selection of which RNA isoforms differentiating cells produce. Many of the genes affected by PNN knockdown are known to affect the epithelial phenotype. This window into the complexity of RNA splicing in the corneal epithelium implies that PNN exerts broad influence over the regulation and maintenance of the epithelial cell phenotype.

Proteomic analysis of proton beam irradiated human melanoma cells

Proton beam irradiation is a form of advanced radiotherapy providing superior distributions of a low LET radiation dose relative to that of photon therapy for the treatment of cancer. Even though this clinical treatment has been developing for several decades, the proton radiobiology critical to the optimization of proton radiotherapy is far from being understood. Proteomic changes were analyzed in human melanoma cells treated with a sublethal dose (3 Gy) of proton beam irradiation. The results were compared with untreated cells. Two-dimensional electrophoresis was performed with mass spectrometry to identify the proteins. At the dose of 3 Gy a minimal slowdown in proliferation rate was seen, as well as some DNA damage. After allowing time for damage repair, the proteomic analysis was performed. In total 17 protein levels were found to significantly (more than 1.5 times) change: 4 downregulated and 13 upregulated. Functionally, they represent four categories: (i) DNA repair and RNA regulation (VCP, MVP, STRAP, FAB-2, Lamine A/C, GAPDH), (ii) cell survival and stress response (STRAP, MCM7, Annexin 7, MVP, Caprin-1, PDCD6, VCP, HSP70), (iii) cell metabolism (TIM, GAPDH, VCP), and (iv) cytoskeleton and motility (Moesin, Actinin 4, FAB-2, Vimentin, Annexin 7, Lamine A/C, Lamine B). A substantial decrease (2.3 x) was seen in the level of vimentin, a marker of epithelial to mesenchymal transition and the metastatic properties of melanoma.

Regulation of Na,K-ATPase β1-subunit in TGF-β2-mediated epithelial-to-mesenchymal transition in human retinal pigmented epithelial cells

Proliferative vitreo retinopathy (PVR) is associated with extracellular matrix membrane (ECM) formation on the neural retina and disruption of the multilayered retinal architecture leading to distorted vision and blindness. During disease progression in PVR, retinal pigmented epithelial cells (RPE) lose cell-cell adhesion, undergo epithelial-to-mesenchymal transition (EMT), and deposit ECM leading to tissue fibrosis. The EMT process is mediated via exposure to vitreous cytokines and growth factors such as TGF-β2. Previous studies have shown that Na,K-ATPase is required for maintaining a normal polarized epithelial phenotype and that decreased Na,K-ATPase function and subunit levels are associated with TGF-β1-mediated EMT in kidney cells. In contrast to the basolateral localization of Na,K-ATPase in most epithelia, including kidney, Na,K-ATPase is found on the apical membrane in RPE cells. We now show that EMT is also associated with altered Na,K-ATPase expression in RPE cells. TGF-β2 treatment of ARPE-19 cells resulted in a time-dependent decrease in Na,K-ATPase β1 mRNA and protein levels while Na,K-ATPase α1 levels, Na,K-ATPase activity, and intracellular sodium levels remained largely unchanged. In TGF-β2-treated cells reduced Na,K-ATPase β1 mRNA inversely correlated with HIF-1α levels and analysis of the Na,K-ATPase β1 promoter revealed a putative hypoxia response element (HRE). HIF-1α bound to the Na,K-ATPase β1 promoter and inhibiting the activity of HIF-1α blocked the TGF-β2 mediated Na,K-ATPase β1 decrease suggesting that HIF-1α plays a potential role in Na,K-ATPase β1 regulation during EMT in RPE cells. Furthermore, knockdown of Na,K-ATPase β1 in ARPE-19 cells was associated with a change in cell morphology from epithelial to mesenchymal and induction of EMT markers such as α-smooth muscle actin and fibronectin, suggesting that loss of Na,K-ATPase β1 is a potential contributor to TGF-β2-mediated EMT in RPE cells.

Pharmacology and rationale for imatinib in the treatment of scleroderma

Systemic sclerosis (scleroderma) is a chronic, multisystem, fibrotic disease. Although the pathogenesis is not completely understood, early vascular damage leads to an inflammatory reaction and a severe fibrotic response. Therapy of systemic sclerosis is still not convincing and is mainly restricted to the management of organ complications. A wide choice of immunosuppressive and antifibrotic drugs has been used to try to modify the course of the disease, but significant breakthroughs are still lacking. Imatinib is a tyrosine kinase inhibitor known to regulate growth, proliferation, and differentiation as well as apoptosis of cells and is already widely used for several malignancies, eg, chronic myeloid leukemia and gastrointestinal stromal tumors. It has been used in preclinical as well as clinical studies to modulate the fibrotic process in patients with systemic sclerosis. This is based on its activity to interfere selectively with both the transforming growth factor-β and platelet-derived growth factor signaling pathway. Preclinical studies in mouse models of scleroderma showed significant anti-inflammatory and antifibrotic effects; however, several clinical, proof-of-concept trials have not yet confirmed these initially promising results.

Phosphorylation of ΔNp63α via a novel TGFβ/ALK5 signaling mechanism mediates the anti-clonogenic effects of TGFβ

Genetic analysis of TP63 implicates ΔNp63 isoforms in preservation of replicative capacity and cellular lifespan within adult stem cells. ΔNp63α is also an oncogene and survival factor that mediates therapeutic resistance in squamous carcinomas. These diverse activities are the result of genetic and functional interactions between TP63 and an array of morphogenic and morphostatic signals that govern tissue and tumor stasis, mitotic polarity, and cell fate; however the cellular signals that account for specific functions of TP63 are incompletely understood. To address this we sought to identify signaling pathways that regulate expression, stability or activity of ΔNp63α. An siRNA-based screen of the human kinome identified the Type 1 TGFβ receptor, ALK5, as the kinase required for phosphorylation of ΔNp63α at Serine 66/68 (S66/68). This activity is TGFβ-dependent and sensitive to either ALK5-directed siRNA or the ALK5 kinase inhibitor A83-01. Mechanistic studies support a model in which ALK5 is proteolytically cleaved at the internal juxtamembrane region resulting in the translocation of the C-terminal ALK5-intracellular kinase domain (ALK5^IKD). In this study, we demonstrate that ALK5-mediated phosphorylation of ΔNp63α is required for the anti-clonogenic effects of TGFΒ and ectopic expression of ALK5^IKD mimics these effects. Finally, we present evidence that ultraviolet irradiation-mediated phosphorylation of ΔNp63α is sensitive to ALK5 inhibitors. These findings identify a non-canonical TGFβ-signaling pathway that mediates the anti-clonogenic effects of TGFβ and the effects of cellular stress via ΔNp63α phosphorylation.

STRAP regulates c-Jun ubiquitin-mediated proteolysis and cellular proliferation

STRAP is a ubiquitous WD40 protein that has been implicated in tumorigenesis. Previous studies suggest that STRAP imparts oncogenic characteristics to cells by promoting ERK and pRb phosphorylation. While these findings suggest that STRAP can activate mitogenic signaling pathways, the effects of STRAP on other MAPK pathways have not been investigated. Herein, we report that STRAP regulates the expression of the c-Jun proto-oncogene in mouse embryonic fibroblasts. Loss of STRAP expression results in reduced phospho-c-Jun and total c-Jun but does not significantly reduce the level of two other early response genes, c-Myc and c-Fos. STRAP knockout also decreases expression of the AP-1 target gene, cyclin D1, which is accompanied by a reduction in cell growth. No significant differences in JNK activity or basal c-Jun mRNA levels were observed between wild type and STRAP null fibroblasts. However, proteasomal inhibition markedly increases c-Jun expression in STRAP knockout MEFs and STRAP over-expression decreases the ubiquitylation of c-Jun in 293T cells. Loss of STRAP accelerates c-Jun turnover in fibroblasts and ectopic over-expression of STRAP in STRAP null fibroblasts increases c-Jun expression. Collectively, our findings indicate that STRAP regulates c-Jun stability by decreasing the ubiquitylation and proteosomal degradation of c-Jun.