Transforming signals resulting from sustained activation of the PDGFbeta receptor in mortal human fibroblasts

Canis Familiaris Papillomavirus Type 26: A Novel Papillomavirus of Dogs and the First Canine Papillomavirus within the Omegapapillomavirus Genus

Domestic dogs are currently recognized as being infected by 25 different canine papillomavirus (CPV) types classified into three genera. A short sequence from a novel CPV type was amplified, along with CPV1, from a papilloma (wart) from the mouth of a dog. The entire 7499 bp genome was amplified, and CPV26 contained putative coding regions that were predicted to produce four early proteins and two late ones. The ORF L1 showed less than 62% similarity for all previously sequenced CPV types but over 69% similarity to multiple Omegapapillomavirus types from a variety of Caniform species including the giant panda, Weddel seal, and polar bear. Phylogenetic analysis confirmed CPV26 clusters within the Omegapapillomavirus genus. Specific primers were used to investigate the presence of CPV26 DNA within a series of 37 canine proliferative lesions. CPV26 DNA was amplified from one lesion, a cutaneous papilloma that also contained CPV6. This is the first time a PV type within the Omegapapillomavirus genus has been detected in a non-domestic species and this provides evidence that the omegapapillomaviruses infected a common ancestor of, and then co-evolved with, the Caniform species. Whether CPV26 causes disease is uncertain, but the absence of an E7 protein may suggest low pathogenicity.

Role of the JNK Pathway in Bladder Cancer

Bladder cancer, one of the most frequently diagnosed cancers worldwide, is associated with high morbidity and mortality and a poor prognosis. The bladder cancer types include 1) non-muscle invasive bladder cancer (NMIBC) and 2) muscle invasive bladder cancer (MIBC). Metastases and chemoresistance in MIBC patients are the leading causes of the high death rate. c-Jun N-terminal kinase (JNK) is an important factor for the undifferentiated state of cancer cells. JNK belongs to the mitogen-activated protein kinases (MAPKs) family; it is activated by various extracellular stimuli, such as stress, radiation, and growth factors and mediates diverse cellular functions, such as apoptosis, autophagy, proliferation, invasion, and migration by mediating AKT (Ak strain transforming), ATG (Autophagy related), mTOR (Mammalian target of rapamycin), and caspases 3, 8, and 9. This review describes the JNK-related functions, mechanisms, and signaling in bladder cancer.

Targeting platelet-derived growth factor receptor β inhibits the proliferation and motility of human pterygial fibroblasts

Background: Pterygium, a common eye disease with high postoperative recurrence, lacks effective therapeutic strategies. Therefore, it's urgent to identify specific targets to develop rationally targeted molecular drugs for the pterygial therapy. Methods: The cell proliferation and motility were studied in both the primary human pterygial fibroblasts (hPFs) and an ex vivo pterygium model. hPFs transfected with the pCMV3-PDGFRB plasmid, PDGFRB siRNA and CRISPR/Cas9 system were used to determine the role of PDGFR-β in pterygial fibroblasts functions. Western blotting, immunohistochemistry and immunofluorescence were performed to evaluate the expression of the key proteins. Results: PDGFR-β expression in the pterygial stroma and primary hPFs was significantly higher than that in the conjunctiva and human conjunctival fibroblasts. PDGF-BB promoted the proliferation, migration and invasion of hPFs, which can be significantly suppressed by sunitinib via inhibition of the PDGFR-β/extracellular signal-regulated kinase (ERK) pathway. In the ex vivo model, the knockout of PDGFRB and sunitinib treatment blocked the proliferation and motility of fibroblasts in the pterygial stroma via the suppression of PDGFR-β/ERK pathway. Conclusion: This study demonstrates that PDGFR-β may be a potential therapeutic target for pterygium, and inhibition of PDGFR-β by sunitinib is a promising and effective approach for pterygium treatment.

Analysis of activated platelet-derived growth factor β receptor and Ras-MAP kinase pathway in equine sarcoid fibroblasts

Equine sarcoids are skin tumours of fibroblastic origin affecting equids worldwide. Bovine papillomavirus type-1 (BPV-1) and, less commonly, type-2 are recognized as etiological factors of sarcoids. The transforming activity of BPV is related to the functions of its major oncoprotein E5 which binds to the platelet-derived growth factor β receptor (PDGFβR) causing its phosphorylation and activation. In this study, we demonstrate, by coimmunoprecipitation and immunoblotting, that in equine sarcoid derived cell lines PDGFβR is phosphorylated and binds downstream molecules related to Ras-mitogen-activated protein kinase-ERK pathway thus resulting in Ras activation. Imatinib mesylate is a tyrosine kinase receptors inhibitor which selectively inhibits the activation of PDGFβR in the treatment of several human and animal cancers. Here we show that imatinib inhibits receptor phosphorylation, and cell viability assays demonstrate that this drug decreases sarcoid fibroblasts viability in a dose-dependent manner. This study contributes to a better understanding of the molecular mechanisms involved in the pathology of sarcoids and paves the way to a new therapeutic approach for the treatment of this common equine skin neoplasm.

The E5 proteins

The E5 proteins are short transmembrane proteins encoded by many animal and human papillomaviruses. These proteins display transforming activity in cultured cells and animals, and they presumably also play a role in the productive virus life cycle. The E5 proteins are thought to act by modulating the activity of cellular proteins. Here, we describe the biological activities of the best-studied E5 proteins and discuss the evidence implicating specific protein targets and pathways in mediating these activities. The primary target of the 44-amino acid BPV1 E5 protein is the PDGF β receptor, whereas the EGF receptor appears to be an important target of the 83-amino acid HPV16 E5 protein. Both E5 proteins also bind to the vacuolar ATPase and affect MHC class I expression and cell-cell communication. Continued studies of the E5 proteins will elucidate important aspects of transmembrane protein-protein interactions, cellular signal transduction, cell biology, virus replication, and tumorigenesis.

Bovine papillomavirus E5 and E7 oncoproteins in naturally occurring tumors: are two better than one?

Bovine papillomaviruses (BPVs) are oncogenic DNA viruses, which mainly induce benign lesions of cutaneous and/or mucosal epithelia in cattle. Thirteen (BPV 1-13) different viral genotypes have been characterized so far. BPVs are usually species-specific but BPV 1/2 may also infect equids as well as buffaloes and bison and cause tumors in these species. BPV-induced benign lesions usually regress, however occasionally they develop into cancer particularly in the presence of environmental carcinogenic co-factors. The major transforming protein of BPV is E5, a very short hydrophobic, transmembrane protein with many oncogenic activities. E5 contributes to cell transformation through the activation of the cellular β receptor for the platelet-derived growth factor (PDGFβ-r), it also decreases cell surface expression of major histocompatibility complex class I (MHCI) causing viral escape from immunosurveillance, and plays a role in the inhibition of the intracellular communication by means of aberrant connexin expression. E7 is considered as a weak transforming gene, it synergies with E5 in cell transformation during cancer development. E7 expression correlates in vivo with the over-expression of β1-integrin, which plays a role in the regulation of keratinocytes proliferation and differentiation. Additionally, E7 is involved in cell-mediated immune responses leading to tumour rejection, in anoikis process by direct binding to p600, and in invasion process by upregulation of Matrix metalloproteinase1 (MMP-1) expression. Studies on the role of BPV E5 and E7 oncoproteins in naturally occurring tumours are of scientific value, as they may shed new light on the biological role of these two oncogenes in cell transformation.

Expression of platelet derived growth factor β receptor, its activation and downstream signals in bovine cutaneous fibropapillomas

Bovine cutaneous fibropapillomas are benign skin tumours formed by proliferation of epidermal keratinocytes and dermal fibroblasts caused by bovine papillomaviruses (BPVs). BPV E5 oncoprotein plays a key role in neoplastic cell transformation by specifically binding to the platelet derived growth factor beta receptor (PDGFβR) causing its phosphorylation and activation of proliferation and survival signal transduction pathways, among these phosphatidyl inositol-3-kinase (PI3K)/Akt and Ras-mitogen-activated-protein-kinase-Erk (Ras-MAPK-Erk) pathways. The aim of this study was to investigate the expression of PDGFβR, its phosphorylation status and expression of the downstream molecules phospho-Akt (pAkt) and phospho-Erk (pErk), in naturally occurring bovine cutaneous fibropapillomas. By immunohistochemistry on serial sections we showed cytoplasmic co-expression of the PDGFβR and E5 protein in neoplastic tissue. Western blot analysis revealed that PDGFβR was phosphorylated in higher amount in tumour samples compared to normal skin. pAkt, but not pErk, was also overexpressed in tumour samples. These findings may provide new insights into the aetiopathogenic mechanisms underlying naturally occurring bovine fibropapillomas and contribute to understanding the molecular scenario underlying BPV induced tumourigenesis.

Papillomavirus E5: the smallest oncoprotein with many functions

Papillomaviruses (PVs) are established agents of human and animal cancers. They infect cutaneous and mucous epithelia. High Risk (HR) Human PVs (HPVs) are consistently associated with cancer of the uterine cervix, but are also involved in the etiopathogenesis of other cancer types. The early oncoproteins of PVs: E5, E6 and E7 are known to contribute to tumour progression. While the oncogenic activities of E6 and E7 are well characterised, the role of E5 is still rather nebulous. The widespread causal association of PVs with cancer makes their study worthwhile not only in humans but also in animal model systems. The Bovine PV (BPV) system has been the most useful animal model in understanding the oncogenic potential of PVs due to the pivotal role of its E5 oncoprotein in cell transformation. This review will highlight the differences between HPV-16 E5 (16E5) and E5 from other PVs, primarily from BPV. It will discuss the targeting of E5 as a possible therapeutic agent.

Activated platelet-derived growth factor β receptor and Ras-mitogen-activated protein kinase pathway in natural bovine urinary bladder carcinomas

Bovine papillomavirus types 1 or 2 (BPV-1/2) are involved in the aetiopathogenesis of bovine urinary bladder cancer. BPV-1/2 E5 activates the platelet-derived growth factor β receptor (PDGFβR). The aim of this study was to analyse the Ras/mitogen-activated protein kinase (MAPK) pathway in relation to activation of PDGFβR in natural bovine urinary bladder carcinomas. Co-immunoprecipitation and Western blot analysis demonstrated that recruitment of growth factor receptor bound protein 2 (GRB-2) and Sos-1 to the activated PDGFβR was increased in carcinomas compared to normal tissues. Higher grade bovine urinary bladder carcinomas were associated with activation of Ras, but not with activation of downstream mitogen-activated protein kinase/extracellular signal-regulated kinase (Mek 1/2) or extracellular signal-regulated kinase (Erk 1/2).

Resveratrol regulates p66Shc activation in HaCaT cells

Skin is exposed to both endogenous and environmental oxidant agents, leading to the harmful generation of reactive oxygen species. Particular interest has been pointed on plant antioxidants, such as resveratrol, because of their wide-ranging biological activity and clinical potential. Resveratrol exerts antioxidant, metabolism-regulating and pro-apoptotic/anti-cancer effects on a variety of experimental models and has been suggested to protect skin from ultraviolet-induced photodamaging and photoaging. In parallel, also the biological significance of p66Shc, a member of the Src Homologue and Collagene homologue family with redox activity, is getting further attention. Because of the striking intersection among the activities of resveratrol with those of p66Shc, we investigated whether resveratrol would activate p66Shc in human immortalised keratinocytes (HaCaT cells), a well known and largely used model for skin keratinocytes. HaCaT cells were treated with resveratrol (10-150 μm) for different times. The effect of resveratrol on the proliferation of HaCaT cells and the activation of ERK1/2, AKT, and p66Shc was investigated by cell counting, fluorescence-activated cell sorting, and western blot analysis of total or immunoprecipitated cell extracts. In HaCaT cells, resveratrol induces dose- and time-dependent growth arrest, p66Shc-Ser36 phosphorylation, ERK1/2 phosphorylation and AKT dephosphorylation. Finally, we showed that resveratrol-induced p66Shc-Ser36 phosphorylation is dependent on ERK1/2 activation. Interestingly, these resveratrol-induced molecular effects were associated with reduced adhesion and reversible growth arrest rather than cell death pathways. This is the first evidence linking resveratrol with p66Shc and suggests that p66Shc may contribute to the effect of resveratrol on cell proliferation and function in the outermost layer of the skin.

Epstein-Barr virus nuclear antigen 3C regulated genes in lymphoblastoid cell lines

EBV nuclear antigen 3C (EBNA3C) is an essential transcription factor for EBV transformed lymphoblast cell line (LCL) growth. To identify EBNA3C-regulated genes in LCLs, microarrays were used to measure RNA abundances in each of three different LCLs that conditionally express EBNA3C fused to a 4-OH-Tamoxifen-dependent estrogen receptor hormone binding domain (EBNA3CHT). At least three RNAs were assayed for each EBNA3CHT LCL under nonpermissive conditions, permissive conditions, and nonpermissive conditions with wild-type EBNA3C transcomplementation. Using a two-way ANOVA model of EBNA3C levels, we identified 550 regulated genes that were at least 1.5-fold up- or down-regulated with false discovery rates < 0.01. EBNA3C-regulated genes overlapped significantly with genes regulated by EBNA2 and EBNA3A consistent with coordinated effects on cell gene transcription. Of the 550 EBNA3C-regulated genes, 106 could be placed in protein networks. A seeded Bayesian network analysis of the 80 most significant EBNA3C-regulated genes suggests that RAC1, LYN, and TNF are upstream of other EBNA3C-regulated genes. Gene set enrichment analysis found enrichment for MAP kinase signaling, cytokine-cytokine receptor interactions, JAK-STAT signaling, and cell adhesion molecules, implicating these pathways in EBNA3C effects on LCL growth or survival. EBNA3C significantly up-regulated the CXCL12 ligand and its CXCR4 receptor and increased LCL migration. CXCL12 up-regulation depended on EBNA3C's interaction with the cell transcription factor, RBPJ, which is essential for LCL growth. EBNA3C also up-regulated MYC 1.3-fold and down-regulated CDKN2A exons 2 and 3, shared by p16 and p14, 1.4-fold, with false discovery rates < 5 × 10(-4).

Phosphatidylinositol-3-kinase-AKT pathway, phospho-JUN and phospho-JNK expression in spontaneously arising bovine urinary bladder tumours

The aetiopathogenesis of urinary bladder tumours in cattle involves prolonged ingestion of bracken fern and infection by bovine papillomavirus types 1 or 2 (BPV-1/2). E5, the major BPV-1/2 oncoprotein, binds to the activated platelet-derived growth factor beta receptor (pPDGF-betaR), inducing cell transformation in vitro and spontaneously arising urinary bladder tumours. The aim of this study was to assess whether the 85 kDa regulatory subunit (p85) of the phosphatidylinositol-3-kinase (PI3K)-AKT pathway and other transforming signals phospho-JUN (pJUN) and phospho-JUN N-terminal kinases (pJNK) may be important in the development of BPV-associated urothelial carcinomas. A physical interaction between the pPDGF-betaR and PI3K was shown in four tumours and two samples of normal bladder tissue by co-immunoprecipitation and western blotting. There was greater expression of the PI3K-AKT-cyclin D3 molecular pathway downstream to the activation of pPDGF-betaR in neoplastic compared with normal tissue. pJNK and pJUN were overexpressed in samples of tumour compared with normal mucosal tissue. These findings provide new insights into the aetiopathogenic mechanisms underlying naturally occurring bovine urothelial carcinogenesis and contribute to understanding of the role of E5 oncoprotein in naturally occurring tumorigenesis.

Papillomavirus-Associated Cutaneous Neoplasia in Mammals

For humans, strong evidence indicates that some mucosal papillomavirus (PV) types cause genital and oral neoplasia, and weaker evidence suggests that some cutaneous PVs may cause cutaneous squamous cell carcinomas (SCC). For nonhuman species, strong evidence supports a causal role of PVs in the development of feline and equine sarcoids. Likewise, PVs are believed to cause cutaneous SCCs in rabbits, western barred bandicoots, and some rodents. Furthermore, some evidence suggests that PVs may influence the development of both feline and canine cutaneous SCCs. This review discusses the evidence that PVs cause human cutaneous SCCs and the proposed mechanisms for this action. It then reviews preneoplastic and neoplastic skin diseases that are associated with PV infection in nonhuman mammals.

Artificial transmembrane oncoproteins smaller than the bovine papillomavirus E5 protein redefine sequence requirements for activation of the platelet-derived growth factor beta receptor

The bovine papillomavirus E5 protein (BPV E5) is a 44-amino-acid homodimeric transmembrane protein that binds directly to the transmembrane domain of the platelet-derived growth factor (PDGF) beta receptor and induces ligand-independent receptor activation. Three specific features of BPV E5 are considered important for its ability to activate the PDGF beta receptor and transform mouse fibroblasts: a pair of C-terminal cysteines, a transmembrane glutamine, and a juxtamembrane aspartic acid. By using a new genetic technique to screen libraries expressing artificial transmembrane proteins for activators of the PDGF beta receptor, we isolated much smaller proteins, from 32 to 36 residues, that lack all three of these features yet still dimerize noncovalently, specifically activate the PDGF beta receptor via its transmembrane domain, and transform cells efficiently. The primary amino acid sequence of BPV E5 is virtually unrecognizable in some of these proteins, which share as few as seven consecutive amino acids with the viral protein. Thus, small artificial proteins that bear little resemblance to a viral oncoprotein can nevertheless productively interact with the same cellular target. We speculate that similar cellular proteins may exist but have been overlooked due to their small size and hydrophobicity.

Imatinib mesylate inhibited rat adjuvant arthritis and PDGF-dependent growth of synovial fibroblast via interference with the Akt signaling pathway

Overgrowth of the synovium plays an important role in the pathogenesis of rheumatoid arthritis (RA). Platelet-derived growth factor (PDGF) is one of the most potent mitogenic factors of synovial cells, and imatinib mesylate (imatinib) is a specific inhibitor of the PDGF receptor tyrosine kinase. The aim of this study was to elucidate the anti-rheumatic activity of imatinib. The in vivo effects of imatinib were assessed by evaluating the sequential manifestation of adjuvant-induced arthritis in rats using paw volume and clinical scores. Imatinib was found to inhibit rat adjuvant-induced arthritis, but the inhibitory effects were incomplete. To confirm the mechanism of anti-rheumatic-activity of imatinib, we assessed the in vitro effects of imatinib on the proliferation of RA synovial fibroblast-like cells (RASFs) using a MTT assay. Intracellular signaling of PDGF was evaluated by Western blot analysis. Platelet-derived growth factor was found to induce a significant proliferation of RASFs, while imatinib inhibited PDGF-induced proliferation of RASF. Imatinib also inhibited PDGF-induced phosphorylation of the PDGF receptor and Akt, whereas constitutive activated extracellular signal-regulated kinase was not inhibited by imatinib. In contrast, imatinib did not inhibit transforming growth factor beta- and basic fibroblast growth factor-induced proliferation of RASF. Oral administration of imatinib ameliorated adjuvant-induced arthritis in rats, and it inhibited PDGF-induced RASF proliferation through disruption of the PDGF-R to Akt kinase signaling pathway. Because imatinib cannot inhibit the non-PDGF-dependent proliferation of RASFs, the anti-rheumatic effect of imatinib may be incomplete. The development of inhibitors of RASF proliferation may lead to the successful treatment of RA.

Activated platelet-derived growth factor beta receptor expression, PI3K-AKT pathway molecular analysis, and transforming signals in equine sarcoids

The equine sarcoid is the most common dermatologic neoplasm reported in horses. Bovine papillomavirus (BPV) types 1 and 2 are associated with sarcoids, in which the expression of the major transforming oncoprotein (E5) is often recorded. The transformation activity of the virus is due to the binding of the E5 to the platelet-derived growth factor beta receptor (PDGFbeta-r). In the present study, we show by Western blot in 4 sarcoid samples and 3 normal equine skin samples that the PDGFbeta-r is more phosphorylated in sarcoid tissue than in normal skin (P < .001). Furthermore, the physical interaction between the activated receptor and the 85-kDa regulatory subunit (p85) of phosphatidylinositol-3-kinase (PI3K) is shown by coimmunoprecipitation. The PI3K-AKT-cyclin D3 molecular pathway downstream to the activation of the PDGFbeta-r is shown to be expressed, and the amount of the investigated molecules is higher than normal (P < .001), suggesting an activation of these effectors in sarcoids. Further, we demonstrate that phospho-JNK and phospho-JUN are more expressed in sarcoids than in normal skin. Our results provide new insights into the pathogenesis of equine sarcoids and support the validity of this in-vivo model to further characterize the molecular pathways underlying BPV E5-induced carcinogenesis.

p66Shc links alpha1-adrenergic receptors to a reactive oxygen species-dependent AKT-FOXO3A phosphorylation pathway in cardiomyocytes

p66Shc is an adapter protein that is induced by hypertrophic stimuli and has been implicated as a major regulator of reactive oxygen species (ROS) production and cardiovascular oxidative stress responses. This study implicates p66Shc in an alpha(1)-adrenergtic receptor (alpha(1)-AR) pathway that requires the cooperative effects of protein kinase (PK)Cepsilon and PKCdelta and leads to AKT-FOXO3a phosphorylation in cardiomyocytes. alpha(1)-ARs promote p66Shc-YY(239/240) phosphorylation via a ROS-dependent mechanism that is localized to caveolae and requires epidermal growth factor receptor (EGFR) and PKCepsilon activity. alpha(1)-ARs also increase p66Shc-S(36) phosphorylation via an EGFR transactivation pathway involving PKCdelta. p66Shc links alpha(1)-ARs to an AKT signaling pathway that selectively phosphorylates/inactivates FOXO transcription factors and downregulates the ROS-scavenging protein manganese superoxide dismutase (MnSOD); the alpha(1)-AR-p66Shc-dependent pathway involving AKT does not regulate GSK3. Additional studies show that RNA interference-mediated downregulation of endogenous p66Shc leads to the derepression of FOXO3a-regulated genes such as MnSOD, p27Kip1, and BIM-1. p66Shc downregulation also increases proliferating cell nuclear antigen expression and induces cardiomyocyte hypertrophy, suggesting that p66Shc exerts an antihypertrophic action in neonatal cardiomyocytes. The novel alpha(1)-AR- and ROS-dependent pathway involving p66Shc identified in this study is likely to contribute to cardiomyocyte remodeling and the evolution of heart failure.

The bovine papillomavirus E5 protein and the PDGF beta receptor: it takes two to tango

The extremely hydrophobic, 44-amino acid bovine papillomavirus (BPV) E5 protein is the smallest known oncoprotein, which orchestrates cell transformation by causing ligand-independent activation of a cellular receptor tyrosine kinase, the platelet-derived growth factor beta receptor (PDGFbetaR). The E5 protein forms a dimer in transformed cells and is essentially an isolated membrane-spanning segment that binds directly to the transmembrane domain of the PDGFbetaR, inducing receptor dimerization, autophosphorylation, and sustained mitogenic signaling. There are few sequence constraints for activity as long as the overall hydrophobicity of the E5 protein and its ability to dimerize are preserved. Nevertheless, the E5 protein is highly specific for the PDGFbetaR and does not activate other cellular proteins. Genetic screens of thousands of small, artificial hydrophobic proteins with randomized transmembrane domains inserted into an E5 scaffold identified proteins with diverse transmembrane sequences that activate the PDGFbetaR, including some activators as small as 32-amino acids. Analysis of these novel proteins has provided new insight into the requirements for PDGFbetaR activation and specific transmembrane recognition in general. These results suggest that small, transmembrane proteins can be constructed and selected that specifically bind to other cellular or viral transmembrane target proteins. By using this approach, we have isolated a 44-amino acid artificial transmembrane protein that appears to activate the human erythropoietin receptor. Studies of the tiny, hydrophobic BPV E5 protein have not only revealed a novel mechanism of viral oncogenesis, but have also suggested that it may be possible to develop artificial small proteins that specifically modulate much larger target proteins by acting within cellular or viral membranes.