Transforming growth factor-beta modulates plasminogen activator activity and plasminogen activator inhibitor type-1 expression in human keratinocytes in vitro

Pharmacologic inhibition of ALK5 causes selective induction of terminal differentiation in mouse keratinocytes expressing oncogenic HRAS

TGFβ has both tumor suppressive and oncogenic roles in cancer development. We previously showed that SB431542 (SB), a small molecule inhibitor of the TGFβ type I receptor (ALK5) kinase, suppressed benign epidermal tumor formation but enhanced malignant conversion. Here, we show that SB treatment of primary K5rTA/tetORASV12G bitransgenic keratinocytes did not alter HRASV12G-induced keratinocyte hyperproliferation. However, continuous SB treatment significantly enhanced HRASV12G-induced cornified envelope formation and cell death linked to increased expression of enzymes transglutaminase (TGM) 1 and TGM3 and constituents of the cornified envelope small proline-rich protein (SPR) 1A and SPR2H. In contrast, TGFβ1 suppressed cornified envelope formation in HRASV12G keratinocytes. Similar results were obtained in HRASV12G transgenic mice treated topically with SB or by coexpressing TGFβ1 and HRASV12G in the epidermis. Despite significant cell death, SB-resistant HRASV12G keratinocytes repopulated the primary culture that had overcome HRas-induced senescence. These cells expressed reduced levels of p16(ink4a) and were growth stimulated by SB but remained sensitive to a calcium-induced growth arrest. Together these results suggest that differential responsiveness to cornification may represent a mechanism by which pharmacologic blockade of TGFβ signaling can inhibit the outgrowth of preneoplastic lesions but may cause a more progressed phenotype in a separate keratinocyte population.

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.

Transforming growth factor-beta requires its target plasminogen activator inhibitor-1 for cytostatic activity

The cytokine transforming growth factor beta (TGFbeta) has strong antiproliferative activity in most normal cells but contributes to tumor progression in the later stages of oncogenesis. It is not fully understood which TGFbeta target genes are causally involved in mediating its cytostatic activity. We report here that suppression of the TGFbeta target gene encoding plasminogen activator inhibitor-1 (PAI-1) by RNA interference leads to escape from the cytostatic activity of TGFbeta both in human keratinocytes (HaCaTs) and primary mouse embryo fibroblasts. Consistent with this, PAI-1 knock-out mouse embryo fibroblasts are also resistant to TGFbeta growth arrest. Conversely, we show that ectopic expression of PAI-1 in proliferating HaCaT cells induces a growth arrest. PAI-1 knockdown does not interfere with canonical TGFbeta signaling as judged by SMAD phosphorylation and induction of bona fide TGFbeta target genes. Instead, knockdown of PAI-1 results in sustained activation of protein kinase B. Significantly, we find that constitutive protein kinase B activity leads to evasion of the growth-inhibitory action of TGFbeta. Our data are consistent with a model in which induction of PAI-1 by TGFbeta is critical for the induction of proliferation arrest.

Regulation of Extracellular Matrix Remodeling following Transforming Growth Factor-β1/Epidermal Growth Factor-Stimulated Epithelial-Mesenchymal Transition in Human Premalignant Keratinocytes

During tumor progression, malignant cells exploit critical developmental and tissue remodeling programs, often promoting a plastic phenotype referred to as an epithelial-mesenchymal transition (EMT). Autocrine/paracrine signaling due to tumor microenvironment cytokines, such as members of the transforming growth factor-beta (TGF-beta) and epidermal growth factor (EGF) families, largely regulates the morphological and invasive phases of the EMT phenotype. Notably, epithelial cell initiation often coincides with a switch in the response of these cells to TGF-beta and is concomitant with EGF receptor amplification. Modeling these events, we have observed that premalignant human keratinocytes, HaCaTs, acquire a highly motile and scattered phenotype indicative of EMT following stimulation with TGF-beta1 and EGF. TGF-beta1 and EGF have been shown to upregulate a number of matrix metalloproteinases (MMP) in epithelial cells, which may in turn play a role in developing metastatic potential in these cells. We have established that an increase in MMP-10 expression occurs following treatment of HaCaT cells with a combination of TGF-beta1 and EGF. This increase in MMP-10 expression paralleled the development of a collagenolytic phenotype that was sensitive to components of the plasminogen activation system, including the plasminogen activator inhibitor type-1 (PAI-1). Significantly high levels of MMP-10 have been detected in squamous cell carcinomas of the head and neck, esophagus, oral cavity and skin. Importantly, TGF-beta1 in addition to upregulating MMP-10 has been shown to upregulate PAI-1 expression in HaCaT cells. Taken together, these observations suggest that TGF-beta1 and EGF play a complex role in modulating proteolytic and transitional events such as EMT that may facilitate the progression of human premalignant epithelial cells toward a more invasive phenotype.

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

The emergence of highly aggressive subtypes of human cutaneous squamous cell carcinoma (SCC) often reflects increased autocrine/paracrine TGF-β synthesis and epidermal growth factor receptor (EGFR) amplification. Cooperative TGF-β/EGFR signaling promotes cell migration and induces expression of both proteases and protease inhibitors that regulate stromal remodeling resulting in acquisition of an invasive phenotype. TGF-β1+EGF stimulation increases the production of several matrix metalloproteinases (MMPs) in human SCC. Among the most prominent is MMP-10 which is 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 up-regulated under these conditions and is an early event in progression of incipient epidermal SCC. A model is proposed in which TGF-β1+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 mechanisms that maintain this elegant balance is critical to developing potential therapeutics for the treatment of human cutaneous malignancies.

Glucose-mediated regulation of transforming growth factor-beta (TGF-beta) and TGF-beta receptors in human retinal endothelial cells

PURPOSE

Diabetic retinopathy is a micro-angiopathy affecting predominantly small vessels of the retina. Clinical trials have demonstrated a strong association between tight glucose control and a reduction in the incidence and the severity of diabetic retinopathy. Transforming growth factor beta (TGF-beta) is involved in the control of endothelial cell proliferation, adhesion, and deposition of extracellular matrix, thus TGF-beta may play a role in the control of endothelial cell proliferation seen in the disease. We wished to investigate the regulation of transforming growth factor beta and its receptors (type I and II) in human retinal endothelial cells exposed to a range of glucose concentrations.

METHODS

Human retinal endothelial cells were isolated from donor eyes, cultured in vitro and exposed to a range of glucose concentrations (0-25 mmol/l). TGF-beta protein and mRNA levels were determined by ELISA and Northern analysis, respectively. The binding affinities and TGF-beta receptor numbers were defined using a binding assay.

RESULTS

Northern hybridisation and ELISA showed that after 8 hours, the level of TGF-beta mRNA and protein was significantly higher at 15mmol/l compared to 5, 20 or 25mmol/ l. Binding assays showed that for high glucose (25 mmol/l), human retinal endothelial cells express a population of TGF-beta receptors with higher affinity for its ligand than at 5 or 15 mmol/l.

CONCLUSIONS

These results demonstrate that glucose regulates TGF-beta mRNA and protein production and also TGF-beta receptor expression in human retinal endothelial cells. Thus, the glucose-mediated changes that occur in diabetic patients may expose human retinal endothelial cells to potential angiogenic factors which may influence disease progression.

Cutaneous small-vessel vasculitis

Cutaneous small-vessel vasculitis (CSVV) refers to a group of disorders usually characterized by palpable purpura; it is caused by leukocytoclastic vasculitis of postcapillary venules. CSVV can be idiopathic or can be associated with a drug, infection, or underlying systemic disease. Initially, the pathogenesis of CSVV is immune complex related, but in its later stages different pathogenetic mechanisms may intensify the reaction and lymphocytes may predominate in the infiltrate. Cure requires elimination of the cause (ie, drugs, chemicals, infections, food allergens) when possible, as well as therapy with nonsteroidal antiinflammatory agents, corticosteroids, dapsone, potassium iodide, fibrinolytic agents, aminocaproic acid, immunosuppressive agents (ie, cyclophosphamide, azathioprine, methotrexate, cyclosporine) or even monoclonal antibodies, depending on disease severity.

Three activator protein-1-binding sites bound by the Fra-2.JunD complex cooperate for the regulation of murine laminin alpha3A (lama3A) promoter activity by transforming growth factor-beta

Several lines of evidence suggest a role for laminin-5 in skin wound healing. We report here that transforming growth factor-beta (TGF-beta), which elicits various responses during cutaneous healing, stimulates transcription of the mouse laminin alpha3A (lama3A) gene. To identify the TGF-beta-responsive elements (TGFbeta-REs) on the lama3A promoter, we have generated a series of 5'-deletions of the promoter upstream of the beta-galactosidase reporter gene. Transient cell transfection assays using mouse PAM212 keratinocytes revealed that TGFbeta-REs lie between nucleotides -297 and -54 relative to the transcription start site. Insertion of the TGFbeta-RE in front of the unresponsive minimal SV40 promoter conferred TGF-beta inducibility. Computer analysis of the promoter sequence identified three canonical activator protein-1 (AP-1) sites located at nucleotides -277 (AP-1A), -125 (AP-1B), and -69 (AP-1C). Site-directed mutagenesis of either the AP-1A or AP-1C site did not drastically alter the basal activity of the lama3A promoter, but reduced TGF-beta responsiveness by 50%. Simultaneous mutation of these two AP-1 sites resulted in a 65% decline in the response to TGF-beta, suggesting a cooperative contribution of each site to the overall promoter activity. In contrast, mutation of the AP-1B site markedly reduced the basal activity of the lama3A promoter, indicating that this AP-1 site is essential for gene expression. Mobility shift assays demonstrated specific binding of Fra-2 and JunD to the AP-1 sites, suggesting for the first time a possible regulatory function for the Fra-2.JunD AP-1 complex in a basal keratinocyte-specific gene.

The differential regulation and secretion of proteinases from fetal and neonatal fibroblasts by growth factors

One of the major differences between fetal and adult wound repair is the unique ability of fetal wounds to heal without scarring. Since scar formation is a function of extracellular matrix deposition, the regulation of this component is fundamental in tissue remodeling. In this study, we have characterized the differences in the secretion of matrix-degrading proteases, namely urokinase plasminogen activator and gelatinase A and B, from fetal and neonatal fibroblasts. In addition, we examined the modulation of these protease levels by growth factors known to be important in wound repair. The results indicate that the secretion of these proteases differ significantly between the two cell types. The levels of urokinase plasminogen activator and its inhibitor were notably higher in media conditioned by neonatal fibroblasts in comparison to fetal samples. In contrast, the basal level of gelatinase A was comparable in both cell types, whilst the level of gelatinase B was elevated in the fetal fibroblasts. Transforming growth factor-beta 1 reduced the level of urokinase plasminogen activator and stimulated the secretion of plasminogen activator inhibitor-1 and progelatinase B in both neonatal and fetal fibroblasts. However, only progelatinase A and an activated form of gelatinase B were significantly elevated in fetal fibroblasts. In contrast, platelet-derived growth factor stimulated urokinase plasminogen activator, its inhibitor and both gelatinase A and B, an effect which was more apparent in fetal fibroblasts. This difference in protease regulation may be reflected in the differing rate and quality of tissue remodeling observed during adult vs fetal wound repair.

Transforming growth factor-beta 1 modulates beta 1 and beta 5 integrin receptors and induces the de novo expression of the alpha v beta 6 heterodimer in normal human keratinocytes: implications for wound healing

The molecular mechanism underlying the promotion of wound healing by TGF-beta 1 is incompletely understood. We report that TGF-beta 1 regulates the regenerative/migratory phenotype of normal human keratinocytes by modulating their integrin receptor repertoire. In growing keratinocyte colonies but not in fully stratified cultured epidermis, TGF-beta 1: (a) strongly upregulates the expression of the fibronectin receptor alpha 5 beta 1, the vitronectin receptor alpha v beta 5, and the collagen receptor alpha 2 beta 1 by differentially modulating the synthesis of their alpha and beta subunits; (b) downregulates the multifunctional alpha 3 beta 1 heterodimer; (c) induces the de novo expression and surface exposure of the alpha v beta 6 fibronectin receptor; (d) stimulates keratinocyte migration toward fibronectin and vitronectin; (e) induces a marked perturbation of the general mechanism of polarized domain sorting of both beta 1 and beta 4 dimers; and (f) causes a pericellular redistribution of alpha v beta 5. These data suggest that alpha 5 beta 1, alpha v beta 6, and alpha v beta 5, not routinely used by keratinocytes resting on an intact basement membrane, act as "emergency" receptors, and uncover at least one of the molecular mechanisms responsible for the peculiar integrin expression in healing human wounds. Indeed, TGF-beta 1 reproduces the integrin expression pattern of keratinocytes located at the injury site, particularly of cells in the migrating epithelial tongue at the leading edge of the wound. Since these keratinocytes are inhibited in their proliferative capacity, these data might account for the apparent paradox of a TGF-beta 1-dependent stimulation of epidermal wound healing associated with a growth inhibitory effect on epithelial cells.

Differential regulation of plasminogen activation in normal keratinocytes and SCC-4 cells by fibroblasts

The plasminogen activator (PA)/plasmin system is thought to be involved in processes such as tumor invasion and wound healing, during which epithelial and mesenchymal cells come close together. However, information on regulation of the PA/plasmin system during epithelial-mesenchymal interactions is scarce. Therefore, we examined the in vitro modulation of the production and activity of the components of the PA/plasmin system in squamous carcinoma cells (SCC-4) and normal human keratinocytes in relation to cell density and the presence or absence of fibroblasts (3T3 cells). There was an inverse relation between cell density and mRNA expression for urokinase-type plasminogen activator (u-PA) and u-PA receptor in both SCC-4 cells and keratinocytes. In addition, such a relation was found for plasminogen activator inhibitor types 1 (PAI-1) and 2 (PAI-2) in SCC-4 monocultures, but not in keratinocyte monocultures. In contrast to monocultures, variation of cell density did not affect the mRNA expression of the components of the PA/plasmin system in cocultures of SCC-4 cells or keratinocytes with 3T3 cells. However, the relative expression of mRNAs in co-cultures was clearly different from that in monocultures, especially at low cell density. For most of the components of the PA/plasmin system, a decrease in mRNA expression and u-PA receptor protein was observed at most cell densities, whereas for PAI-1 only in keratinocytes a marked increase was documented. Zymography of supernatants revealed that the levels of both free u-PA and PA-PAI were increased in SCC-4/3T3 co-cultures, whereas in keratinocytes/3T3 co-cultures, only levels of the PA-PAI complex were increased, while the amount of free u-PA activity decreased. This occurred despite the increase u-PA immunoreactivity and was probably caused by the markedly elevated levels of immunoreactive PAI-1. The results of the present study reveal that the production and synthesis of various components of the PA/plasmin system in keratinocytes and SCC-4 cells depend on the density of epithelial cells and are modulated by fibroblasts, probably through a direct cell-cell or cell-matrix contact. Fibroblast-induced modulations are similar in keratinocytes and SCC-4 cells except for the regulation of PAI-1, which is markedly enhanced only in keratinocytes. This suggests that the modulation of PA activity in the direct microenvironment may be different under physiologic and pathologic conditions.

Calcium-independent increases in pericellular plasminogen activator activity in pemphigus vulgaris

Intracellular free calcium ([Ca2+]i), an important second messenger, plays a crucial role in a variety of biochemical reactions leading to cell activation and protein secretion. This study examines the potential role of [Ca2+]i in mediating increases in pericellular plasminogen activator activity of canine keratinocytes observed upon binding of human pemphigus vulgaris IgG (hPV IgG). Using the calcium-sensitive fluorescent probe fura-2 and digital video fluorescence imaging microscopy, [Ca2+]i levels were determined in individual keratinocytes for up to 29 minutes after addition of 0.1-5 mg/ml hPV IgG to monolayers of subconfluent and confluent cultures. Extracellular ATP (a known [Ca2+]i-agonist in canine keratinocytes) and normal human IgG (nh IgG) served as positive and negative controls, respectively. HPV IgG and nh IgG failed to induce significant increases in [Ca2+]i, whereas 500 microM ATP induced a rapid, 3- to 12-fold transient increase above resting levels. Binding of hPV IgG to these keratinocyte cultures was demonstrated by immunofluorescence at the end of selected experiments. ATP stimulation of cultures previously treated with hPV IgG showed normal responsiveness and more than 90% of the cells were still viable at the end of [Ca2+]i imaging, thus demonstrating that failure to respond to hPV IgG was not due to an experimental artifact. Plasminogen activator activity in supernatants of confluent cultures incubated with 0.1-1 mg/ml hPV IgG or nh IgG and harvested at various time intervals was dependent on the IgG dose used and increased steadily over time. Increases in activity were 47-92% higher in cultures treated with hPV IgG than those incubated with the same dose of nh IgG.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor beta as a neuronoglial signal during peripheral nervous system response to injury

In contrast to the central nervous system (CNS), the peripheral nervous system (PNS) displays an important regenerative ability which is dependent, at least in part, on Schwann cell properties. The mechanisms which stimulate Schwann cells to adapt their behavior after a lesion to generate adequate conditions for PNS regeneration remain unknown. In this work, we report that adult rat dorsal root ganglion (DRG) neurons are able, after a lesion performed in vivo or when they are dissociated and cultured in vitro, to synthesize transforming growth factor beta (TGF beta), a pleiotropic growth factor implicated in wound healing processes and in carcinogenesis. This TGF beta is tentatively identified as the beta-1 isoform. Adult rat DRG neurons release a biologically active form of TGF beta which is able to elicit multiple Schwann cell responses including a stimulation to proliferate. Moreover, purified TGF beta-1 produces a Schwann cell morphology alteration and decreases the secretion of tissue-type plasminogen activator (tPA) and enhances the secretion of plasminogen activator inhibitor (PAI) by Schwann cells. This generates conditions which are thought to favor a successful neuritic regrowth. Furthermore, purified TGF beta-1 stimulates type IV collagen mRNA expression in Schwann cells. This subtype of collagen is associated with the process of myelinization. Finally, TGF beta-1 decreases nerve growth factor (NGF) mRNA expression by Schwann cells, an effect which could participate in the maintenance of a distoproximal NGF gradient during nerve regeneration. We propose that neuronal TGF beta plays an essential role as a neuronoglial signal that modulates the response of Schwann cells to injury and participates in the successful regeneration processes observed in the PNS.

Enhanced production of plasminogen activator activity in human and murine keratinocytes by transforming growth factor-beta 1

Transforming growth factor-beta (TGF beta) is the most potent known inhibitor of keratinocyte growth. Pericellular proteolytic activity is usually high in proliferating and malignant cells and decreased in resting or growth-arrested cells. We have therefore analyzed the effects of TGF beta 1 on the production of plasminogen activator activity by normal human keratinocytes and a mouse keratinocyte cell line under serum-free conditions. The plasminogen activator activity of the culture medium was analyzed using caseinolysis-in-agar and zymography assays, immunoblotting, and Northern hybridization analysis for the plasminogen activators (PA) and PA inhibitor-1 (PAI-1). Alterations of radiolabeled polypeptides were observed in fluorograms of gels. It was found that like in human epidermoid carcinoma cells picomolar concentrations of TGF beta 1 (0.2-20 ng/ml) enhanced total plasminogen activator activity in both keratinocyte cell systems. Zymographic and immunoblotting analyses of the medium indicated that the activator was of the urokinase type (u-PA). Immunoprecipitation and Concanavalin A affinity chromatography of the culture medium indicated that the cells also started to produce PAI-1. Analysis of the pericellular matrix preparations of the keratinocytes showed that PAI-1 is deposited to the pericellular space. Evidently due to elevated u-PA activity PAI-1 was removed from the extracellular matrix more rapidly in TGF beta 1-treated cells than from control cultures. Northern hybridization analysis of human keratinocytes showed that TGF beta 1 rapidly elevated both u-PA and PAI-1 mRNA levels. Comparison of the temporal induction profiles indicated that the mRNA for u-PA increased more slowly but was more persistent than that of PAI-1. Actinomycin D inhibited the induction of both u-PA and PAI-1 mRNA, suggesting that the induction was due to increased transcription. The results suggest that enhanced plasminogen activator activity can be associated with growth inhibition also in nonmalignant cells like cultured human or murine keratinocytes.