PAI-1 is a Critical Upstream Regulator of the TGF-beta1/EGF-Induced Invasive Phenotype in Mutant p53 Human Cutaneous Squamous Cell Carcinoma

Stromal Factors as a Target for Immunotherapy in Melanoma and Non-Melanoma Skin Cancers

Immune checkpoint inhibitors (ICIs), such as anti-programmed cell death 1 (PD1) antibodies (Abs) and anti-cytotoxic T-lymphocyte associated protein 4 (CTLA4) Abs, have been widely administered for not only advanced melanoma, but also various non-melanoma skin cancers. Since profiles of tumor-infiltrating leukocytes (TILs) play important roles in immunotherapy using ICIs, it is important to evaluate cancer stromal cells such as tumor-associated macrophages (TAMs) and cancer-associated fibroblasts (CAFs), as well as stromal extracellular matrix protein, to predict the efficacy of ICIs. This review article focuses particularly on TAMs and related factors. Among TILs, TAMs and their related factors could be the optimal biomarkers for immunotherapy such as anti-PD1 Ab therapy. According to the studies presented, TAM-targeting therapies for advanced melanoma and non-melanoma skin cancer will develop in the future.

Cancer-Associated Fibroblasts: Mechanisms of Tumor Progression and Novel Therapeutic Targets

Simple Summary

The tumor microenvironment plays an important role in determining the biological behavior of several of the more aggressive malignancies. Among the various cell types evident in the tumor “field”, cancer-associated fibroblasts (CAFs) are a heterogenous collection of activated fibroblasts secreting a wide repertoire of factors that regulate tumor development and progression, inflammation, drug resistance, metastasis and recurrence. Insensitivity to chemotherapeutics and metastatic spread are the major contributors to cancer patient mortality. This review discusses the complex interactions between CAFs and the various populations of normal and neoplastic cells that interact within the dynamic confines of the tumor microenvironment with a focus on the involved pathways and genes.

Abstract

Cancer-associated fibroblasts (CAFs) are a heterogenous population of stromal cells found in solid malignancies that coexist with the growing tumor mass and other immune/nonimmune cellular elements. In certain neoplasms (e.g., desmoplastic tumors), CAFs are the prominent mesenchymal cell type in the tumor microenvironment, where their presence and abundance signal a poor prognosis in multiple cancers. CAFs play a major role in the progression of various malignancies by remodeling the supporting stromal matrix into a dense, fibrotic structure while secreting factors that lead to the acquisition of cancer stem-like characteristics and promoting tumor cell survival, reduced sensitivity to chemotherapeutics, aggressive growth and metastasis. Tumors with high stromal fibrotic signatures are more likely to be associated with drug resistance and eventual relapse. Clarifying the molecular basis for such multidirectional crosstalk among the various normal and neoplastic cell types present in the tumor microenvironment may yield novel targets and new opportunities for therapeutic intervention. This review highlights the most recent concepts regarding the complexity of CAF biology including CAF heterogeneity, functionality in drug resistance, contribution to a progressively fibrotic tumor stroma, the involved signaling pathways and the participating genes.

Prostaglandin E2 receptor 3 (EP3) signaling promotes migration of cervical cancer via urokinase-type plasminogen activator receptor (uPAR)

Purpose

Cervical cancer metastasis results in poor prognosis and increased mortality, which is not separated from inflammatory reactions accumulated by prostaglandin E2 (PGE2). As a specific G-protein coupled PGE2 receptor, EP3 is demonstrated as a negative prognosticator of cervical malignancy. Now, we aimed to investigate the pathological mechanism of EP3 in modulating cervical cancer carcinogenesis.

Methods

Bioinformatics analysis was used to identify PAI-1 and uPAR correlations with EP3 expression, as well as the prognosis of cervical cancer patients. In vitro analyses were carried out to investigate the role of EP3 on cervical cancer proliferation and migration.

Results

In vitro studies showed that sulprostone (an EP3 agonist) enhanced the proliferation and migration of cervical cancer cells, whereas silencing of EP3 inhibited their proliferation and migration. Furthermore, EP3 knockdown increased the expression of plasminogen activator inhibitor type 1 (PAI-1), urokinase-type plasminogen activator receptor (uPAR), and phosphorylated extracellular signal-regulated kinases 1/2 (p-ERK1/2), but decreased p53 expression. Bioinformatics analysis showed that both PAI-1 and uPAR were correlated with EP3 expression, as well as the prognosis of cervical cancer patients. The survival analysis further showed that uPAR overexpression (IRS≥2) was correlated with a lower overall survival rate of cervical cancer patients with advanced stages (FIGO III-IV).

Conclusion

These results indicated that EP3 signaling pathway might facilitate the migration of cervical cancer cells through modulating uPAR expression. Therefore, EP3 and uPAR could represent novel therapeutic targets in the treatment of cervical cancer in advantaged stages.

Electronic supplementary material

The online version of this article (10.1007/s00432-020-03272-0) contains supplementary material, which is available to authorized users.

Plasminogen activator inhibitor-1 in cancer research

[Despite as a major inhibitor of urokinase (uPA), paradoxically,] Plasminogen activator inhibitor-1 (PAI-1) has been validated to be highly expressed in various types of tumor biopsy tissues or plasma compared with controls based on huge clinical data bases analysis, more importantly, PAI-1 alone or in conjunction with uPA have been identified as prognostic for disease progression and relapse in certain cancer types. particularly in breast cancer. In addition to play important roles in cell adhesion, migration and invasion, PAI-1 has been reported to induce tumor vascularization and thus promote cell dissemination and tumor metastasis. Furthermore, there are many tumor promoting factors involved in the modulation of PAI-1 expression and activity, which will strengthen the pro-tumorigenic roles of PAI-1. Undoubtedly, PAI-1 may be a promising target for therapeutic intervention of specific cancer treatment. In fact, some PAI-1 inhibitors are currently being evaluated in cancer therapy, which may be developed to new antitumor agents in the future.

Stress granules counteract senescence by sequestration of PAI-1

Cellular senescence is a physiological response by which an organism halts the proliferation of potentially harmful and damaged cells. However, the accumulation of senescent cells over time can become deleterious leading to diseases and physiological decline. Our data reveal a novel interplay between senescence and the stress response that affects both the progression of senescence and the behavior of senescent cells. We show that constitutive exposure to stress induces the formation of stress granules (SGs) in proliferative and presenescent cells, but not in fully senescent cells. Stress granule assembly alone is sufficient to decrease the number of senescent cells without affecting the expression of bona fide senescence markers. SG‐mediated inhibition of senescence is associated with the recruitment of the plasminogen activator inhibitor‐1 (PAI‐1), a known promoter of senescence, to these entities. PAI‐1 localization to SGs increases the translocation of cyclin D1 to the nucleus, promotes RB phosphorylation, and maintains a proliferative, non‐senescent state. Together, our data indicate that SGs may be targets of intervention to modulate senescence in order to impair or prevent its deleterious effects.

Endothelium-derived microparticles from chronically thromboembolic pulmonary hypertensive patients facilitate endothelial angiogenesis

Background

Increased circulating levels of endoglin⁺ endothelial microparticles (EMPs) have been identified in several cardiovascular disorders, related to severity. Endoglin is an auxilary receptor for transforming growth factor β (TGF-β) important in the regulation of vascular structure.

Results

We quantified the number of microparticles in plasma of six patients with chronic thromboembolic pulmonary hypertension (CTEPH) and age- and sex-matched pulmonary embolic (PE) and healthy controls and investigated the role of microparticle endoglin in the regulation of pulmonary endothelial function in vitro. Results show significantly increased levels of endoglin⁺ EMPs in CTEPH plasma, compared to healthy and disease controls. Co-culture of human pulmonary endothelial cells with CTEPH microparticles increased intracellular levels of endoglin and enhanced TGF-β-induced angiogenesis and Smad1,5,8 phosphorylation in cells, without affecting BMPRII expression. In an in vitro model, we generated endothelium-derived MPs with enforced membrane localization of endoglin. Co-culture of these MPs with endothelial cells increased cellular endoglin content, improved cell survival and stimulated angiogenesis in a manner similar to the effects induced by overexpressed protein.

Conclusions

Increased generation of endoglin⁺ EMPs in CTEPH is likely to represent a protective mechanism supporting endothelial cell survival and angiogenesis, set to counteract the effects of vascular occlusion and endothelial damage.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-016-0224-9) contains supplementary material, which is available to authorized users.

Krüppel-Like Factor 4 Inhibits the Transforming Growth Factor-β1-Promoted Epithelial-to-Mesenchymal Transition via Downregulating Plasminogen Activator Inhibitor-1 in Lung Epithelial Cells

Transforming growth factor-β (TGF-β) signaling and TGF-β-promoted epithelial-to-mesenchymal transition (EMT) have been postulated to be the common pathway causing pulmonary fibrosis. However, the up- or downstreaming markers of TGF-β-induced EMT still need to be further recognized. In the present study, we investigated the regulation on Krüppel-like factor 4 (KLF-4) and plasminogen activator inhibitor-1 (PAI-1) by TGF-β in the murine lung epithelial LA-4 cells and then examined the regulation of both markers in the TGF-β-induced EMT by the PAI-1 knockdown or the KLF-4 overexpression. Our study indicated that TGF-β induced EMT in mouse LA-4 lung epithelial cells via reducing E-cadherin, while promoting Collagen I and α-SMA. And PAI-1 was upregulated, whereas KLF-4 was downregulated in the TGF-β-induced EMT model in LA-4 cells. Moreover, the siRNA-mediated PAI-1 knockdown inhibited the TGF-β-induced EMT, whereas the adenovirus-medicated KLF-4 overexpression markedly reduced the PAI-1 expression and inhibited the TGF-β-induced EMT in LA-4 cells. In conclusion, our study confirmed the downregulation of KLF-4 in the TGF-β-induced EMT in LA-4 cells. And the KLF-4 overexpression significantly reduced the TGF-β-induced PAI-1 and thus inhibited the TGF-β-induced EMT in mouse lung epithelial LA-4 cells. It implies that KLF-4 might be a promising target for effective control of the pulmonary fibrosis.

SERPINE1: A Molecular Switch in the Proliferation-Migration Dichotomy in Wound-"Activated" Keratinocytes

Significance: A highly interactive serine protease/plasmin/matrix metalloproteinase axis regulates stromal remodeling in the wound microenvironment. Current findings highlight the importance of stringent controls on protease expression and their topographic activities in cell proliferation, migration, and tissue homeostasis. Targeting elements in this cascading network may lead to novel therapeutic approaches for fibrotic diseases and chronic wounds. Recent Advances: Matrix-active proteases and their inhibitors orchestrate wound site tissue remodeling, cell migration, and proliferation. Indeed, the serine proteases urokinase plasminogen activator and tissue-type plasminogen activator (uPA/tPA) and their major phsyiological inhibitor, plasminogen activator inhibitor-1 (PAI-1; serine protease inhibitor clade E member 1 [SERPINE1]), are upregulated in several cell types during injury repair. Coordinate expression of proteolytic enzymes and their inhibitors in the wound bed provides a mechanism for fine control of focal proteolysis to facilitate matrix restructuring and cell motility in complex environments. Critical Issues: Cosmetic and tissue functional consequences of wound repair anomalies affect the quality of life of millions of patients in the United States alone. The development of novel therapeutics to manage individuals most affected by healing anomalies will likely derive from the identification of critical, translationally accessible, control elements in the wound site microenvironment. Future Directions: Activation of the PAI-1 gene early after wounding, its prominence in the repair transcriptome and varied functions suggest a key role in the global cutaneous injury response program. Targeting PAI-1 gene expression and/or PAI-1 function with molecular genetic constructs, neutralizing antibodies or small molecule inhibitors may provide a novel, therapeutically relevant approach, to manage the pathophysiology of wound healing disorders associated with deficient or excessive PAI-1 levels.

cmvIL-10 stimulates the invasive potential of MDA-MB-231 breast cancer cells

Cancer is the result of unregulated cell growth that leads to tumor formation, and in many cases, metastases. Although there are several risk factors associated with cancer, one area that remains poorly understood is the impact of infectious disease. Human cytomegalovirus (HCMV) is a member of the herpesvirus family that is highly prevalent in the population. HCMV usually causes clinical disease only in immune compromised individuals, but recent evidence suggests that HCMV may be strongly associated with some forms of cancer, particularly glioblastoma and breast cancer. We investigated the possibility that cmvIL-10, a viral cytokine with homology to human IL-10 that is secreted from infected cells, could act in a paracrine manner to alter the tumor microenvironment, induce cell signaling, and increase the invasive potential of cancer cells. We found that human MDA-MB-231 breast cancer cells express the IL-10 receptor and that exposure to cmvIL-10 results in activation of Stat3, a transcription factor strongly associated with enhanced metastatic potential and chemo-resistance. In addition, cmvIL-10 stimulated an increase in DNA synthesis and cell proliferation, protected MDA-MB-231 cells from etoposide-induced apoptosis, and also greatly enhanced chemotaxis toward epidermal growth factor (EGF). These results suggest a significant and wide-ranging role for cmvIL-10 in the progression of breast cancer and could have broad implications for the diagnosis and treatment of cancer in HCMV-positive patients.

Progesterone receptor isoforms PRA and PRB differentially contribute to breast cancer cell migration through interaction with focal adhesion kinase complexes

Conditionally expressed progesterone receptor isoforms PRA and PRB enhance breast cancer cell migration through interaction with focal adhesion kinase (FAK) and differential regulation of FAK phosphorylation and turnover. PRB-stimulated migration is reduced by progestins, which is prevented by PR antagonists or agonist-bound PRA.

Progesterone receptor (PR) and progestins affect mammary tumorigenesis; however, the relative contributions of PR isoforms A and B (PRA and PRB, respectively) in cancer cell migration remains elusive. By using a bi-inducible MDA-MB-231 breast cancer cell line expressing PRA and/or PRB, we analyzed the effect of conditional PR isoform expression. Surprisingly, unliganded PRB but not PRA strongly enhanced cell migration as compared with PR(–) cells. 17,21-Dimethyl-19-norpregna-4,9-dien-3,20-dione (R5020) progestin limited this effect and was counteracted by the antagonist 11β-(4-dimethyl­amino)­phenyl-17β-hydroxy-17-(1-propynyl)­estra-4,9-dien-3-one (RU486). Of importance, PRA coexpression potentiated PRB-mediated migration, whereas PRA alone was ineffective. PR isoforms differentially regulated expressions of major players of cell migration, such as urokinase plasminogen activator (uPA), its inhibitor plasminogen activator inhibitor type 1, uPA receptor (uPAR), and β1-integrin, which affect focal adhesion kinase (FAK) signaling. Moreover, unliganded PRB but not PRA enhanced FAK Tyr397 phosphorylation and colocalized with activated FAK in cell protrusions. Because PRB, as well as PRA, coimmunoprecipitated with FAK, both isoforms can interact with FAK complexes, depending on their respective nucleocytoplasmic trafficking. In addition, FAK degradation was coupled to R5020-dependent turnovers of PRA and PRB. Such an effect of PRB/PRA expression on FAK signaling might thus affect adhesion/motility, underscoring the implication of PR isoforms in breast cancer invasiveness and metastatic evolution with underlying therapeutic outcomes.

Synergistic and multidimensional regulation of plasminogen activator inhibitor type 1 expression by transforming growth factor type β and epidermal growth factor

The major physiological inhibitor of plasminogen activator, type I plasminogen activator inhibitor (PAI-1), controls blood clotting and tissue remodeling events that involve cell migration. Transforming growth factor type β (TGFβ) and epidermal growth factor (EGF) interact synergistically to increase PAI-1 mRNA and protein levels in human HepG2 and mink Mv1Lu cells. Other growth factors that activate tyrosine kinase receptors can substitute for EGF. EGF and TGFβ regulate PAI-1 by synergistically activating transcription, which is further amplified by a decrease in the rate of mRNA degradation, the latter being regulated only by EGF. The combined effect of transcriptional activation and mRNA stabilization results in a rapid 2-order of magnitude increase in the level of PAI-1. TGFβ also increases the sensitivity of the cells to EGF, thereby recruiting the cooperation of EGF at lower than normally effective concentrations. The contribution of EGF to the regulation of PAI-1 involves the MAPK pathway, and the synergistic interface with the TGFβ pathway is downstream of MEK1/2 and involves phosphorylation of neither ERK1/2 nor Smad2/3. Synergism requires the presence of both Smad and AP-1 recognition sites in the promoter. This work demonstrates the existence of a multidimensional cellular mechanism by which EGF and TGFβ are able to promote large and rapid changes in PAI-1 expression.

EGF/TGFβ1 co-stimulation of oral squamous cell carcinoma cells causes an epithelial-mesenchymal transition cell phenotype expressing laminin 332

Epithelial-mesenchymal transition (EMT) is suggested to be crucial for the development of an invasive and metastatic carcinoma cell phenotype. Therefore, the definition of this phenotype is of great clinical interest. We recently evidenced vimentin positive cells in oral squamous cell carcinoma (OSCC) invasive front expressing laminin γ2 chain mRNA implicating an EMT origin of these cells. To further elucidate the nature of these cells, we have investigated the relation between EMT criteria and laminin-332 expression in a cell culture model of transforming growth factor beta-1 (TGFβ1)/epithelial growth factor (EGF) long time co-stimulation. We demonstrate that in contrast to TGFβ1 or EGF alone, co-stimulation induces phenotype transition in OSCC cells which fulfils the criteria of EMT in terms of vimentin up-regulation and E-cadherin down-regulation on protein level as well as cell scattering. Furthermore, cells displayed a strongly enhanced invasiveness and adhesion to type I-IV collagens. Phenotype transition is accompanied by an enhanced expression of laminin-332, especially of its γ2 chain. We further analyse the expression of extracellular matrix related genes by RT-PCR profiling. With respect to strongly enhanced proteins, data confirm the EMT phenotype of co-stimulated OSCC cells and expression of laminin-332. Furthermore, alpha catenin, collagen type 16, the integrin α7 and β1 chains, and MMP11 are suggested as candidates with potential role in EMT in OSCC. In summary we are able to show that EMT in OSCC is mediated by multiple growth factors and is accompanied by laminin γ2 chain up-regulation evidencing the existence of an intermediate Vim(+) /Ln332(+) EMT phenotype as seen in situ.

PAI-1 mediates the TGF-beta1+EGF-induced "scatter" response in transformed human keratinocytes

Cooperative interactions between growth factor signaling pathways are important elements in carcinoma progression. A model system combining transforming growth factor-beta1 (TGF-beta1) and EGF was developed to investigate mechanisms underlying induced epithelial-to-mesenchymal transition (EMT) in ras-transformed human (HaCaT II-4) keratinocytes. Dual stimulation with TGF-beta1+EGF resulted in keratinocyte "plasticity" and pronounced colony dispersal. The most highly expressed transcript, identified by mRNA profiling, encoded plasminogen activator inhibitor-1 (PAI-1; SERPINE1). PAI-1 negatively regulates plasmin-dependent matrix degradation, preserving a stromal scaffold permissive for keratinocyte motility. Mitogen-activated extracellular kinase (MEK)/extracellular signal-regulated kinase (ERK) and p38 signaling were required for maximal PAI-1 upregulation and TGF-beta1+EGF-stimulated cell locomotion, as pharmacologic disruption of MEK/p38 activity ablated both responses. Moreover, PAI-1 knockdown alone effectively inhibited TGF-beta1+EGF-dependent cell scattering, indicating a functional role for this SERPIN in the dual-growth factor model of induced motility. Moreover, EGFR signaling blockade or EGFR knockdown attenuated TGF-beta1-induced PAI-1 expression, implicating EGFR transactivation in TGF-beta1-stimulated PAI-1 expression, and reduced colony dispersal in TGF-beta1+EGF-treated cultures. Identification of such cooperative signaling networks and their effect on specific invasion-promoting target genes, such as PAI-1, may lead to the development of pathway-specific therapeutics that affect late-stage events in human tumor progression.

Persistent plasminogen activator inhibitor 1 gene expression in cardiac transplant recipients with idiopathic dilated cardiomyopathy

OBJECTIVES

Plasminogen activator inhibitor 1 is the primary regulator of urokinase plasminogen activator and tissue plasminogen activator. Plasminogen activator inhibitor 1 is essential in the control of the thrombotic/fibrinolytic balance and is a marker of endothelial cell injury. Idiopathic dilated cardiomyopathy is reportedly associated with endothelial cell dysfunction. Whether endothelial cell damage plays a role in patients with dilated cardiomyopathy after cardiac transplantation remains unknown.

METHODS

In this study explanted hearts of cardiac transplant recipients with ischemic cardiomyopathy and dilated cardiomyopathy, as well as control myocardial tissue, were investigated for expression of urokinase plasminogen activator, tissue plasminogen activator, urokinase plasminogen activator receptor, and plasminogen activator inhibitor 1 and 2. Furthermore, plasminogen activator inhibitor 1 expression was examined in endomyocardial biopsy specimens and sera of patients with ischemic cardiomyopathy and those with dilated cardiomyopathy during the first posttransplantation year. The effect of the patient's serum on endothelial cells was assessed in vitro to examine the role of circulating endothelial cell damage-related factors.

RESULTS

Plasminogen activator inhibitor 1 expression was upregulated in ischemic cardiomyopathy and dilated cardiomyopathy myocardial tissue versus that seen in control tissue. After transplantation, plasminogen activator inhibitor 1 expression returned to control levels in patients with ischemic cardiomyopathy. In patients with dilated cardiomyopathy, plasminogen activator inhibitor 1 expression increased at 24 weeks after transplantation in both biopsy specimens and sera versus that seen in control tissue. Sera of patients with dilated cardiomyopathy, but not that of patients with ischemic cardiomyopathy, inhibited vascular endothelial growth factor A-induced proliferation of endothelial cells, although downstream target gene activation of early growth response factor 1 and NGFI-A binding protein 2 was not affected.

CONCLUSIONS

These data suggest for the first time that the endothelial cell damage-related process recurs in patients with dilated cardiomyopathy after transplantation, which, independently of vascular endothelial growth factor, is associated with increased plasminogen activator inhibitor 1 expression, and that this pathology might play a role in allograft remodeling in patients with dilated cardiomyopathy.

Unimpeded skin carcinogenesis in K14-HPV16 transgenic mice deficient for plasminogen activator inhibitor

Angiogenesis, extracellular matrix remodeling and cell migration are associated with cancer progression and involve at least, the plasminogen activating system and its main physiological inhibitor, the plasminogen activator inhibitor-1 (PAI-1). Considering the recognized importance of PAI-1 in the regulation of tumor angiogenesis and invasion in murine models of skin tumor transplantation, we explored the functional significance of PAI-1 during early stages of neoplastic progression in the transgenic mouse model of multistage epithelial carcinogenesis (K14-HPV16 mice). We have studied the effect of genetic deletion of PAI-1 on inflammation, angiogenesis, lymphangiogenesis and tumor progression. In this model, PAI-1 deficiency neither impaired keratinocyte hyperproliferation or tumor development nor affected the infiltration of inflammatory cells and development of angiogenic or lymphangiogenic vasculature. We are reporting evidence for concomitant lymphangiogenic and angiogenic switches independent to PAI-1 status. Taken together, these data indicate that PAI-1 is not rate limiting for neoplastic progression and vascularization during premalignant progression, or that there is a functional redundancy between PAI-1 and other tumor regulators, masking the effect of PAI-1 deficiency in this long-term model of multistage epithelial carcinogenesis.

PAI-1 Regulates the Invasive Phenotype in Human Cutaneous Squamous Cell Carcinoma

The emergence of highly aggressive subtypes of human cutaneous squamous cell carcinoma (SCC) often reflects increased autocrine/paracrine TGF-beta synthesis and epidermal growth factor receptor (EGFR) amplification. Cooperative TGF-beta/EGFR signaling promotes cell migration and induces expression of both proteases and protease inhibitors that regulate stromal remodeling resulting in the acquisition of an invasive phenotype. In one physiologically relevant model of human cutaneous SCC progression, TGF-beta1+EGF stimulation increases the production of several matrix metalloproteinases (MMPs), among the most prominent of which is MMP-10-an MMP known to be elevated in SCC in situ. Activation of stromal plasminogen appears to be critical in triggering downstream MMP activity. Paradoxically, PAI-1, the major physiological inhibitor of plasmin generation, is also upregulated under these conditions and is an early event in progression of incipient epidermal SCC. One testable hypothesis proposes that TGF-beta1+EGF-dependent MMP-10 elevation directs focalized matrix remodeling events that promote epithelial cell plasticity and tissue invasion. Increased PAI-1 expression serves to temporally and spatially modulate plasmin-initiated pericellular proteolysis, further facilitating epithelial invasive potential. Defining the complex signaling and transcriptional mechanisms that maintain this delicate balance is critical to developing targeted therapeutics for the treatment of human cutaneous malignancies.

TGF-β1-Induced Expression of the Anti-Apoptotic PAI-1 Protein Requires EGFR Signaling

TGF-β1 and its target gene encoding plasminogen activator inhibitor-1 (PAI-1) are major regulators of capillary outgrowth, vessel maturation and angiogenic network stability. The increasing realization of the complexity of PAI-1 action in the vascular system requires analysis of specific signaling events that impact its expression in a physiologically-relevant cell system. PAI-1 was required for tubular differentiation and maintenance of cellular survival in complex gels since targeted disruption of PAI-1 synthesis or activity with antisense constructs or function-blocking antibodies resulted in network regression. Indeed, serum-deprivation-induced apoptosis of tubulogenic T2 cells was concentration-dependently inhibited by addition of a stable PAI-1 mutant protein consistent with the established pro-survival role of PAI-1 in vascular endothelial cells. PAI-1 induction and ERK pathway activation in response to TGF-β1 was attenuated by EGFR signaling blockade (with AG1478) or preincubation with the MMP/ADAM inhibitor GM6001. The combination of AG1478 + GM6001 completely ablated both responses suggesting that EGFR transactivation is important in PAI-1 gene control and may, at least partially, involve ligand shedding. TGF-β1-stimulated PAI-1 induction was preceded, in fact, by EGFR phosphorylation on Y845 (a src kinase target residue). EGFR1 knockdown with lentiviral shRNA constructs, moreover, effectively decreased (by >75%) TGF-β1-stimulated PAI-1 expression whereas infection with control (i.e. GFP) viruses had no effect. TGF-β1 failed to induce PAI-1 synthesis in EGFR-deficient fibroblasts while introduction of a wild-type EGFR1 construct in EGFR(-/-) cells rescued the PAI-1 response to TGF-β1 confirming, at a genetic level, the targeted knockdown data. The continued clarification of novel cooperative signaling cascades that impact expression of important angiogenic genes (e.g. PAI-1) may provide therapeutically useful targets to manage the pathophysiology of human neoplastic and vascular diseases.

TGF-beta1-Induced Expression of the Poor Prognosis SERPINE1/PAI-1 Gene Requires EGFR Signaling: A New Target for Anti-EGFR Therapy

Increased transforming growth factor-β (TGF-β) expression and epidermal growth factor receptor (EGFR) amplification accompany the emergence of highly aggressive human carcinomas. Cooperative signaling between these two growth factor/receptor systems promotes cell migration and synthesis of stromal remodeling factors (i.e., proteases, protease inhibitors) that, in turn, regulate tumor invasion, neo-angiogenesis and inflammation. ranscript profiling of transformed human cells revealed that genes encoding wound healing, matrix remodeling and cell cycle proteins (i.e., the “tissue repair” transcriptome) are significantly up-regulated early after growth factor stimulation. The major inhibitor of plasmin generation, plasminogen activator inhibitor-1 (PAI-1), is among the most highly induced transcripts during the phenotypic transition initiated by TGF-β maximal expression requires EGFR signaling. PAI-1 induction occurs early in the progression of incipient epidermal squamous cell carcinoma (SCC) and is a significant indicator of poor prognosis in epithelial malignancies. Mouse modeling and molecular genetic analysis of complex systems indicates that PAI-1 regulates the temporal/spatial control of pericellular proteolysis, promotes epithelial plasticity, inhibits capillary regression and facilitates stromal invasion. Defining TGF-β1-initiated signaling events that cooperate with an activated EGFR to impact the protease-protease inhibitor balance in the tumor microenvironment is critical to the development of novel therapies for the clinical management of human cancers.

PAI-1 and functional blockade of SNAI1 in breast cancer cell migration

Introduction

Snail, a family of transcriptional repressors implicated in cell movement, has been correlated with tumour invasion. The Plasminogen Activation (PA) system, including urokinase plasminogen activator (uPA), its receptor and its inhibitor, plasminogen activator inhibitor type 1(PAI-1), also plays a key role in cancer invasion and metastasis, either through proteolytic degradation or by non-proteolytic modulation of cell adhesion and migration. Thus, Snail and the PA system are both over-expressed in cancer and influence this process. In this study we aimed to determine if the activity of SNAI1 (a member of the Snail family) is correlated with expression of the PA system components and how this correlation can influence tumoural cell migration.

Methods

We compared the invasive breast cancer cell-line MDA-MB-231 expressing SNAI1 (MDA-mock) with its derived clone expressing a dominant-negative form of SNAI1 (SNAI1-DN). Expression of PA system mRNAs was analysed by cDNA microarrays and real-time quantitative RT-PCR. Wound healing assays were used to determine cell migration. PAI-1 distribution was assessed by immunostaining.

Results

We demonstrated by both cDNA microarrays and real-time quantitative RT-PCR that the functional blockade of SNAI1 induces a significant decrease of PAI-1 and uPA transcripts. After performing an in vitro wound-healing assay, we observed that SNAI1-DN cells migrate more slowly than MDA-mock cells and in a more collective manner. The blockade of SNAI1 activity resulted in the redistribution of PAI-1 in SNAI1-DN cells decorating large lamellipodia, which are commonly found structures in these cells.

Conclusions

In the absence of functional SNAI1, the expression of PAI-1 transcripts is decreased, although the protein is redistributed at the leading edge of migrating cells in a manner comparable with that seen in normal epithelial cells.

Integration of non-SMAD and SMAD signaling in TGF-beta1-induced plasminogen activator inhibitor type-1 gene expression in vascular smooth muscle cells

Overexpression of plasminogen activator inhibitor-1 (SERPINE1, PAI-1), the major physiological inhibitor of pericellular plasmin generation, is a significant causative factor in the progression of vascular disorders (e.g. arteriosclerosis, thrombosis, perivascular fibrosis) as well as a biomarker and a predictor of cardiovascular-disease associated mortality. PAI-1 is a temporal/spatial regulator of pericellular proteolysis and ECM accumulation impacting, thereby, vascular remodeling, smooth muscle cell migration, proliferation and apoptosis. Within the specific context of TGF-beta1-initiated vascular fibrosis and neointima formation, PAI-1 is a member of the most prominently expressed subset of TGF-beta1-induced transcripts. Recent findings implicate EGFR/pp60c-src-->MEK/ERK1/2 and Rho/ROCK-->SMAD2/3 signaling in TGF-beta1-stimulated PAI-1 expression in vascular smooth muscle cells. The EGFR is a direct upstream regulator of MEK/ERK1/2 while Rho/ROCK modulate both the duration of SMAD2/3 phosphorylation and nuclear accumulation. E-box motifs (CACGTG) in the PE1/PE2 promoter regions of the human PAI-1 gene, moreover, are platforms for a MAP kinase-directed USF subtype switch (USF-1-->USF-2) in response to growth factor addition suggesting that the EGFR-->MEK/ERK axis impacts PAI-1 expression, at least partly, through USF-dependent transcriptional controls. This paper reviews recent data suggesting the essential cooperativity among the EGFR-->MAP kinase cascade, the Rho/ROCK pathway and SMADs in TGF-beta1-initiated PAI-1 expression. The continued clarification of mechanistic controls on PAI-1 transcription may lead to new targeted therapies and clinically-relevant options for the treatment of vascular diseases in which PAI-1 dysregulation is a major underlying pathogenic feature.

Smad4-dependent TGF-beta signaling suppresses RON receptor tyrosine kinase-dependent motility and invasion of pancreatic cancer cells

Transforming growth factorbeta (TGF-beta) signals through Smad-dependent and Smad-independent pathways. However, Smad signaling is altered by allelic deletion or intragenic mutation of the Smad4 gene in more than half of pancreatic ductal adenocarcinomas. We show here that loss of Smad4-dependent signaling leads to aberrant expression of RON, a phosphotyrosine kinase receptor, and that signaling by RON cooperates with Smad4-independent TGF-beta signaling to promote cell motility and invasion. Restoring Smad4 expression in a pancreatic ductal adenocarcinoma cell line that is deficient in Smad4 repressed RON expression. Conversely, small interference RNA knock down of Smad4 or blocking TGF-beta signaling with a TGF-beta type I receptor kinase inhibitor in Smad4-intact cell lines induced RON expression. TGF-beta-induced motility and invasion were inhibited in cells that express Smad4 and that have low levels of RON compared with isogenically matched cells that were deficient in Smad4. Furthermore, knocking down RON expression in Smad4-deficient cells suppressed TGF-beta-mediated motility and invasion. We further determined that Smad4-dependent signaling regulated RON expression at the transcriptional level by real-time reverse transcription PCR and RON promoter luciferase reporter assays. Functional inactivation by site-directed mutations of two Smad binding sites on the RON promoter inhibited TGF-beta-mediated repression of RON promoter activity. These studies indicate that loss of Smad4 contributes to aberrant RON expression and that cross-talk of Smad4-independent TGF-beta signaling and the RON pathway promotes an invasive phenotype.