Urokinase and tissue type plasminogen activators in human keratinocyte culture

Transient Hyperproliferation of a Transgenic Human Epidermis Expressing Hepatocyte Growth Factor

Hepatocyte growth factor (HGF) is a fibroblast-derived protein that affects the growth, motility, and differentiation of epithelial cells including epidermal keratinocytes. To investigate the role of HGF in cutaneous biology and to explore the possibility of using it in a tissue engineering approach, we used retroviral-mediated gene transfer to introduce the gene encoding human HGF into diploid human keratinocytes. Modified cells synthesized and secreted significant levels of HGF in vitro and the proliferation of keratinocytes expressing HGF was enhanced compared with control unmodified cells. To investigate the effects of HGF in vivo, we grafted modified keratinocytes expressing HGF onto athymic mice using acellular dermis as a substrate. When compared with controls, HGF-expressing keratinocytes formed a hyperproliferative epidermis. The epidermis was thicker, had more cells per length of basement membrane, and had increased numbers of Ki-67-positive proliferating cells, many of which were suprabasal in location. Hyperproliferation subsided and the epidermis was equivalent to controls by 2 weeks, a time frame that coincides with healing of the graft. Transient hyperproliferation may be linked to the loss of factors present in the wound that activate HGF. These data suggest that genetically modified skin substitutes secreting HGF may have applications in wound closure and the promotion of wound healing.

Tranexamic acid: an important adjuvant in the treatment of melasma

This article reviews an old drug tranexamic acid to its new use in the treatment of melasma. Its mechanism of preventing the activation of melanocyte from UV light, hormone and injured kerationcyte through the inhibition of the plasminogen activator system will be explored. The detail usage for such indication and its safety profile will also be thoroughly evaluated.

Tissue plasminogen activator in psoriasis

Elevated levels of the serine proteinase plasminogen activator are observed in psoriatic lesions. In contrast to normal epidermis, lesional psoriatic epidermis contains primarily tissue type plasminogen activator (tPA) activity and much lower levels of urokinase type plasminogen activator (uPA) activity. Tissue plasminogen activator is also detectable immunocytochemically in lesional psoriatic but not normal epidermis. Similarly, mRNA for tPA is observed in lesional epidermis only. These results suggest that lesional psoriatic epidermis synthesizes enhanced levels of tPA compared to normal. Additional data support the hypothesis that enhanced tPA may be another marker common to psoriatic epidermis, epidermis during wound repair, and keratinocytes in culture. The significance of elevated tPA in psoriatic lesions is presently unclear, but its possible relationship to epidermal proliferation and cutaneous inflammation is under study.

Elevated expression and release of tissue-type, but not urokinase-type, plasminogen activator after binding of autoantibodies to bullous pemphigoid antigen 180 in cultured human keratinocytes

In bullous pemphigoid (BP), the binding of BP180-specific antibodies to their hemidesmosomal target antigen is not sufficient for blister formation, but must be accompanied by the release of proteases. Using plasminogen activator (PA) knock-out mice, the PA system has previously been shown to be a prerequisite for blister formation in experimental murine BP. Here, we found elevated levels of plasmin and tPA, but not of uPA, in blister fluid from BP patients (n = 7) compared to blisters from patients with toxic epidermal necrolysis (n = 4) and suction blisters in healthy controls (n = 7). Subsequently, we addressed the question whether keratinocytes release PA in response to the binding of anti-BP180 antibodies. Treatment of cultured normal human keratinocytes with BP IgG, but not with control IgG, led to both increased protein and mRNA levels of tPA, but not of uPA, as determined by ELISA and RT-PCR, respectively. The specificity of this finding was confirmed using BP180-deficient keratinocytes from a patient with generalized atrophic benign epidermolysis bullosa, where no tPA release was observed after stimulation with BP IgG. Our results show the elevated expression and release of tPA from normal human keratinocytes upon stimulation with antibodies to human BP180. Keratinocytes, by secreting tPA, may thus play an active role in blister formation of BP.

Elimination of hydrocortisone from the medium enables tissue plasminogen activator gene expression by normal and immortalized nonmalignant human epithelial cells

Human cervical epithelial cells transfected and immortalized with human papillomavirus type 16 DNA (HCE16/3) can be, like many other epithelial cells, normally grown in medium supplemented with epidermal growth factor, cholera toxin, hydrocortisone, insulin, transferrin, thyroid hormone and serum. We found that hydrocortisone diminished tissue plasminogen activator (tPA) production to an undetectable level. The removal of hydrocortisone increased urokinase plasminogen activator (uPA) activity within 24-48 h and tPA activity within 48-72 h, and converted the cells to a more elongated and fibroblastic phenotype. Upregulation of uPA mRNA was seen as early as at 3 h and of tPA mRNA within 48-72 h. Higher molecular weight forms (97-110 kDa) of plasminogen activators were seen in zymograms, apparently complexed with PAI-1, starting at 6 h both in the presence and absence of hydrocortisone. Immunoprecipitation with a PAI-1 monoclonal antibody confirmed that both uPA and tPA were complexed. We also studied normal diploid human bronchial epithelial cells (NHBE) and NHBE cells transformed with an adeno-12/SV40 hybrid virus (BEAS-2B). In both types of nonmalignant epithelial cells, the removal of hydrocortisone increased uPA activity. The omission of hydrocortisone increased tPA levels significantly in BEAS-2B cell cultures, and in NHBE cell cultures tPA became detectable at 72 h. No PA complexes were seen in these two cell types. We conclude that normal and immortalized nonmalignant epithelial cells produce tPA, but only if hydrocortisone is omitted in the growth medium.

Differential effects of acute and chronic wound fluids on urokinase-type plasminogen activator, urokinase-type plasminogen activator receptor, and tissue-type plasminogen activator in cultured human keratinocytes and fibroblasts

The effect of wound fluids collected from acute well-healing wounds and chronic nonhealing venous leg ulcers on the plasminogen activation system of keratinocyte and fibroblast cell cultures was studied in a simplified wound-healing model. Acute wound fluid was collected from donor sites of split skin grafts at different time points representing the progressive healing of the wound. Urokinase-type plasminogen activator, tissue-type plasminogen activator, urokinase-type plasminogen activator receptor, and plasminogen activator inhibitor 1 expression were studied. The methods used were immunocapture assay and immunocytochemistry. The results indicated that the later the acute wound fluid was collected, the greater the urokinase-type plasminogen activator and the lower the plasminogen inhibitor-1 level in treated cells. In contrast, the level of urokinase-type plasminogen activator receptor remained stable irrespective of wound fluid treatment. Immunostaining for urokinase-type plasminogen activator of acute wound fluid-treated cells showed a disseminated punctate pattern over the cell surface, but with chronic wound fluid, urokinase-type plasminogen activator was localized to focal contacts. Our findings support the view that in the acute wound environment the plasminogen activator system is proteolytically active and that in chronic leg ulcers urokinase-type plasminogen activator and urokinase-type plasminogen activator receptor may also be organized for cell adhesion and migration.

Migration of keratinocytes through tunnels of digested fibrin

We report here a hitherto undescribed form of cell migration. When a suspension of human keratinocytes is plated on a fibrin matrix, single cells invade the matrix and progress through it as rounded cells by dissolving the fibrin and thereby creating tunnels. These tunnels are cylindrical or helical, the latter being the result of constant change in the path of cellular advance around the helical axis. Helical tunnel formation is strongly promoted by epidermal growth factor. The rate of migration of the cell through the track of a helical tunnel (up to 2.1 mm per day) is about 7-fold greater than through a cylindrical tunnel. Pericellular fibrinolysis leading to tunnel formation depends on the presence of plasminogen in the medium and its conversion to plasmin by a cellular activator. Formation of tunnels requires that plasminogen activator be localized on the advancing surface of the keratinocyte; we propose that the tunnel is cylindrical when the site of release of plasmin is located at a fixed point on the cell surface and helical when the site of release precesses.

Long-term regeneration of human epidermis on third degree burns transplanted with autologous cultured epithelium grown on a fibrin matrix

BACKGROUND

Extensive third degree burn wounds can be permanently covered by the transplantation of autologous cultured keratinocytes. Many modifications to Green and colleagues' original technique have been suggested, including the use of a fibrin matrix. However, the properties of the cultured cells must be assessed using suitable criteria before a modified method of culture for therapeutic purposes is transferred to clinical use, because changes in culture conditions may reduce keratinocyte lifespan and result in the loss of the transplanted epithelium.

METHODS

To evaluate the performances of human keratinocytes grown on a fibrin matrix, we assay for their colony-forming ability, their growth potential and their ability to generate an epidermis when grafted onto athymic mice. The results of these experiments allowed us to compare side by side the performance for third degree burn treatment of autologous cultured epithelium grafts grown according to Rheinwald and Green on fibrin matrices with that of grafts grown directly on plastic surfaces.

RESULTS

We found that human keratinocytes cultured on a fibrin matrix had the same growth capacity and transplantability as those cultured on plastic surfaces and that the presence of a fibrin matrix greatly facilitated the preparation, handling, and surgical transplantation of the grafts, which did not need to be detached enzymatically. The rate of take of grafts grown on fibrin matrices was high, and was similar to that of conventionally cultured grafts. The grafted autologous cells are capable of generating a normal epidermis for many years and favor the regeneration of a superficial dermis.

CONCLUSION

We have demonstrated that: 1) fibrin matrices have considerable advantages over plastic for the culture of skin cells for grafting and that it is now possible to generate and transplant enough cultured epithelium from a small skin biopsy to restore completely the epidermis of an adult human in 16 days; and 2) the generated epidermis self-renews itself for years. The use of fibrin matrices thus significantly improves the transplantation of cultured epithelium grafts for extensive burns as recently demonstrated in a follow-up work.

In vitro and in vivo expression of interleukin-1alpha and tumor necrosis factor-alpha mRNA in pemphigus vulgaris: interleukin-1alpha and tumor necrosis factor-alpha are involved in acantholysis

Keratinocyte-derived cytokines have been implicated in the pathogenesis of a number of skin diseases. In this study we examined the possible role of keratinocyte-derived cytokines in the development of acantholysis in pemphigus vulgaris. Nineteen patients with pemphigus vulgaris, demonstrating the characteristic clinical, pathologic, and immunopathologic findings were studied. In situ immunolabeling demonstrated the presence of two cytokines interleukin-1alpha and tumor necrosis factor-alpha, in lesional and perilesional areas. Results were confirmed by reverse transcriptase-polymerase chain reaction, demonstrating overexpression of both cytokines in vivo. To study the role of these cytokines in the pathogenesis of pemphigus vulgaris both in vitro and in vivo studies were performed. The results of the in vitro study demonstrated that pemphigus vulgaris IgG induced interleukin-1alpha and tumor necrosis factor-alpha mRNA in the skin. The potential pathogenic role of these mediators was demonstrated by a blocking study using antibodies against human interleukin-1alpha and tumor necrosis factor-alpha in keratinocytes cultures. A combination of anti-interleukin-1alpha and anti-tumor necrosis factor-alpha antibodies inhibited in vitro pemphigus vulgaris IgG induced acantholysis. To confirm the role of interleukin-1 and tumor necrosis factor-alpha in pemphigus, we utilized passive transfer studies using interleukin-1 deficient mice (ICE-/-, interleukin-1beta-/-) and tumor necrosis factor-alpha receptor deficient mice (TNFR1R2-/-). Both groups demonstrated a decreased susceptibility to the passive transfer of pemphigus. Our data support the role of cytokines interleukin-1 and tumor necrosis factor-alpha in the pathogenesis of pemphigus vulgaris.

Protein C inhibitor is expressed in keratinocytes of human skin

Protein C inhibitor is a member of the serpin family that inhibits a variety of serine proteases. Protein C inhibitor is present in numerous body fluids and is produced in the liver and by various epithelial cells. To determine if this epithelial serpin is present in skin, immunohistochemical studies were performed that showed strong staining for protein C inhibitor antigen in the epidermis. Protein C inhibitor mRNA was detected in the keratinocyte cell line HaCaT and the epidermoid carcinoma cell line A431 using reverse transcription-polymerase chain reaction suggesting that also in normal skin protein C inhibitor is derived from keratinocytes. Conditioned media from these cell lines were analyzed on immunoblots, which revealed a protein C inhibitor-antigen band that comigrated with protein C inhibitor derived from the hepatoma cell line HepG2. Using an enzyme-linked immunosorbent assay specific for total protein C inhibitor antigen the accumulation of protein C inhibitor in the cell culture supernatants of HaCaT keratinocytes was found to be 0.3 ng per h per 1 million cells. This is similar to the amount of plasminogen activator inhibitor-1 produced by these cells, which also produce tissue plasminogen activator and urokinase. Fluorescence-activated cell sorter analysis revealed similar expression of intracellular protein C inhibitor antigen in proliferating and confluent HaCaT cells. These findings demonstrate that protein C inhibitor antigen is present in the normal epidermis and that protein C inhibitor is constitutively expressed by keratinocytes in culture. Therefore, protein C inhibitor may provide protease inhibitory activity not only to internal, but also to the external surface of the body. Additionally, protein C inhibitor could contribute to the regulation of retinoid supply in the epidermis, as we have shown recently that retinoic acid binds specifically to protein C inhibitor.

Hydrocortisone regulates the dynamics of plasminogen activator and plasminogen activator inhibitor expression in cultured murine keratinocytes

The plasminogen activators tPA and uPA, and their inhibitors, PAI-1 and PAI-2, have been associated with epithelial homeostasis and wound healing. In these studies, we investigate the effect of the steroid hormone hydrocortisone, a commonly used therapeutic modality for skin, on PAs/PAIs in serum- and plasminogen-free primary cultures of murine keratinocytes. SDS-PAGE fibrin zymography showed that addition of 1 microM hydrocortisone to cultures significantly reduced tPA fibrinolytic activity in both cell extracts and conditioned medium. uPA activity in conditioned medium was similarly inhibited. Cells were also cultured in the presence of dibutyryl cyclic AMP (dbcAMP). dbcAMP (5 mM) alone enhanced uPA and tPA fibrinolytic activity in conditioned medium, but this increase was diminished in the presence of 1 microM hydrocortisone. Immunoblots revealed a three- to fivefold induction of free PAI-1 by hydrocortisone which was partially blocked by dbcAMP. Northern blots showed that PAI-1 mRNA increased threefold 2 h after addition of hydrocortisone and remained elevated at least 8 h. In contrast, uPA and tPA mRNA were unchanged over the same time course. uPA, tPA, and PAI-1 mRNA increased in the presence of dbcAMP; levels remained elevated at least 8 h. HC suppressed the induction of uPA and tPA by dbcAMP. Studies directed at identifying plasminogen mRNA showed that in this culture system, keratinocytes produce no plasminogen mRNA either in the presence or in the absence of hydrocortisone or dbcAMP. Collectively, these results show that keratinocyte plasminogen activator activity is suppressed by hydrocortisone as a function of increased PAI-1 combined with an attenuation of PA induction by agents that increase intracellular cAMP. These results provide additional information to further define the mechanism by which glucocorticoids inhibit wound healing.

Plasminogen activator inhibitor type 2 is expressed in keratinocytes during re-epithelialization of epidermal defects

Plasminogen activation is observed in the human epidermis during re-epithelialization of epidermal defects. The activation reaction depends on plasminogen activators (PAs) associated with re-epithelializing keratinocytes. PA inhibitor type 2 (PAI-2) is thought to be a major epidermal PA inhibitor in keratinocytes. However, no data are available on the expression of PAI-2 in keratinocytes during epidermal regeneration. We have therefore analysed PAI-2 at the mRNA and protein level in keratinocyte cultures as well as in epidermal lesions in which re-epithelializing keratinocytes were apparent. We found that PAI-2 expression at the mRNA and protein level was negatively correlated with the cell density in regular keratinocyte cultures. In organotypic cocultures, in which the transition from a re-epithelializing to a sedentary phenotype can be studied, PAI-2 was most strongly expressed in early cultures prior to formation of a differentiated epidermis-like structure. We found a strong expression of PAI-2 in keratinocytes that re-epithelialized dermal burn wounds or lesions caused by the autoimmune blistering disease pemphigus vulgaris. Our results suggest that not only PAs, but also a major PA inhibitor, PAI-2, are expressed in keratinocytes that are actively involved in re-epithelialization.

Plasminogen activator system in pemphigus vulgaris

Pemphigus vulgaris (PV) is caused by autoantibodies against desmosomes and is characterized by intra-epidermal blisters. The pathology of PV has been linked with plasminogen activation in lesional epidermis. The plasminogen activator system (PA system) consists of urokinase-type plasminogen activator (uPA), tissue-type PA (tPA), as well as the two types of plasminogen activator inhibitors (PAI-1 and PAI-2). In keratinocytes, uPA binds to a specific cell surface receptor for uPA (uPA-R = CD87) in an autocrine manner. Cell-bound uPA is regulated by PAIs. The central PA system component plasminogen, which is present in plasma and interstitial fluids, is bound to the keratinocyte surface via plasmin(ogen) binding sites, where it can be activated by uPA-R-bound uPA. Cell surface-associated plasmin then mediates pericellular proteolysis. As the topographical organization of the distinct PA system components in lesional epidermis of PV remained elusive, we have performed the present immunohistological analysis of lesional and non-lesional epidermis of PV. In keratinocytes directly involved in the epidermal split formation, plasmin(ogen) was stained in nine of 10 cases, uPA-R and uPA in four of 10 cases and PAI-2 in seven of 10 cases. Together, acantholytic plasmin(ogen)+ keratinocytes appeared in three different phenotypes: uPA-R+/uPA+ and PAI-2+, uPA-R-/uPA- and PAI-2+, as well as uPA-R-/uPA- and PAI-2-. Our findings demonstrate that, in acantholytic keratinocytes of PV, PAs and PAIs appear as differentially regulated components of the PA system.

The proteolytic potential of normal human melanocytes: comparison with other skin cells and melanoma cell lines

To understand the contribution of epidermal melanocytes in the proteolytic potential of human skin, we have studied melanocytes grown in a low-serum medium deprived of phorbol esters, cholera toxin, and other non-physiological supplements. We focused on the plasminogen activation system and certain matrix metalloproteinases (gelatinases). Supposing that the proteolytic activity of cells can influence binding to collagen matrix and its reorganization, we have analyzed these parameters as well. We found that human melanocytes secreted tissue-type plasminogen activator and utilised it to generate cell-bound plasmin. No urokinase-type plasminogen activator was detected in the cultures but its receptor was found in cell extracts. Both the 72 kDa and 92 kDa gelatinases were secreted by the cells and in equal amounts. In addition, melanocytes secreted the wide-spectrum proteinase inhibitor alpha-2-macroglobulin. Melanocytes cast into collagen matrices retained a rounded morphology, did not extend processes, and were unable to contract collagen lattices. As a control, these parameters were investigated in parallel in cultures of human keratinocytes, dermal fibroblasts, and two melanoma cell lines. The obtained characteristics suggest that normal human melanocytes are proteolytically active cells. This function may pertain to skin physiology and pathophysiology.

Interleukin-1 beta upregulates tissue-type plasminogen activator in a keratinocyte cell line (HaCaT)

Human keratinocytes synthesize and secrete tissue-type plasminogen activator (tPA). tPA converts the inactive precursor enzyme plasminogen into the trypsin-like proteinase plasmin. tPA is not found in normal epidermis, but in lesional epidermis from patients with a variety of cutaneous diseases, including psoriasis, pemphigus and pemphigoid. The presence of tPA is probably a reaction to the disease process rather than the initiating event in these etiologically and histopathologically diverse lesions. However, the factor(s) that upregulate tPA expression and secretion in keratinocytes have remained largely elusive. We sought to determine whether the inflammatory cytokine interleukin-1 beta (IL-1 beta), which is commonly present in diverse epidermal lesions, influences tPA production. Accordingly, we studied the influence of IL-1 beta on secretion of tPA by cells of the human keratinocyte cell line HaCaT. We found that IL-1 beta increased tPA secretion in these cells. Given the observation that IL-1 beta is a common proinflammatory mediator in cutaneous diseases, our findings may explain the increase in tPA in clinically and etiologically diverse inflammatory epidermal lesions.

Protein kinase C mediates up-regulation of urokinase and its receptor in the migrating keratinocytes of wounded cultures, but urokinase is not required for movement across a substratum in vitro

Both in cell culture and in vivo, keratinocytes that are migrating in response to a wound express enhanced levels of both urokinase-type plasminogen activator (uPA) and the uPA cell surface receptor (uPA-R). To explore the mechanism of this up-regulation, keratinocyte cultures were treated proir to wounding with a variety of metabolic and growth factor inhibitors in order to evaluate their effect on uPA and uPA-R expression. Actinomycin D and cycloheximide inhibited the up-regulation of both uPA and uPA-R, as determined by immunohistochemistry, indicating that RNA and protein syntheses are required for their induction in migrating keratinocytes. Neither removal of protein growth factors from the medium nor addition of inhibitory antibodies to a number of growth factors depressed uPA or uPA-R induction; these findings suggest that a variety of exogenous or endogenous growth factors [i.e., basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), amphiregulin, and tumor necrosis factor-alpha (TNF-alpha) do not have a critical role in the induction of uPA or uPA-R. In contrast, when protein kinase C (PKC) was either down-regulated with bryostatin 5 or inhibited with Ro31-8220 or staurosporine, the expression of both uPA and uPA-R was greatly decreased in migrating keratinocytes. Furthermore, pharmacologic activation of PKC enhanced uPA levels in non-wounded cultures. These data suggest that the enhanced expression of uPA and uPA-R in migrating keratinocytes is mediated by selective activation of PKC in these cells, perhaps secondary to alterations in the cytoskeleton induced by wounding. To test the requirement for uPA during keratinocyte migration in vitro, the extent of migration was quantified in the presence and absence of a variety of inhibitors in the wounded culture model. Migration was not altered by actinomycin D, cycloheximide, any of the above growth factor inhibitors, anti-uPA antibodies, a variety of inhibitors of uPA or plasmin enzymatic activity, or exogenous uPA. The independence of keratinocyte migration in vitro from uPA was further suggested by experiments which combined the phagokinetic assay of migration and the zymographic assay for pericellular uPA activity; no relationship was observed between pericellular uPA activity and the motility of individual cells.

Serum is a potent stimulator of keratinocyte tissue plasminogen activator expression

The plasminogen activator (PA) proteolytic cascade comprises two enzymes known as urokinase PA (uPA) and tissue PA (tPA), both of which activate plasminogen to plasmin. In normal human epidermis uPA is the predominant PA. In lesional epidermis from patients with a variety of cutaneous diseases, including psoriasis, pemphigus foliaceous, pemphigus, vulgaris, bullous pemphigoid, and benign chronic pemphigus, however, tPA is selectively elevated and becomes the predominant PA activity. The enhanced tPA is likely to be a reaction to the disease challenge rather than an initiating event in these clinically and etiologically diverse lesions. In the present study, cultured human keratinocytes, propagated under serum-free conditions, have been shown to respond to the addition of bovine or human serum with an increase in tPA activity and antigen. Furthermore, tPA is found predominantly in the suprabasal keratinocytes both in lesional epidermis and in stratified cultures that have been incubated for approximately 8 d in the presence of serum. These results suggest a possible mechanism by which epidermal tPA may be increased in diverse cutaneous lesions: The plasma infiltrated into lesional epidermis may stimulate the suprabasal keratinocytes in vivo to express tPA.

Epidermal growth factor-binding protein activates soluble and receptor-bound single chain urokinase-type plasminogen activator

Epidermal growth factor-binding protein (EGF-BP) is a serine proteinase that reversibly associates with epidermal growth factor (EGF). We analyzed the reaction of EGF-BP with urokinase type plasminogen activator (u-PA), a serine proteinase that promotes pericellular proteolysis and cellular migration. EGF-BP cleaved single chain u-PA (scu-PA) between Lys158 and Ile159, converting the zymogen into enzymatically active two-chain u-PA (tcu-PA), as shown by SDS-PAGE, N-terminal sequence analysis, and enzymatic assay. The kcat and Km of the activation reaction were (5.6 +/- 0.6) x 10(-2)s-1 and 2.0 +/- 0.3 microM, yielding a catalytic efficiency of 2.8 x 10(4) M-1.s-1. EGF-BP also activated scu-PA bound to receptors on U937 monocytes as demonstrated by the generation of amidase activity against a tcu-PA-specific fluorogenic substrate. By activating scu-PA, EGF-BP may initiate u-PA-dependent cell surface proteolysis and therefore enhance EGF activities that require cellular migration and/or tissue remodeling.

tPA of human keratinocytes: contribution to cell surface-associated plasminogen activation and upregulation by retinoic acid

We tested distinct variants of a human keratinocyte line (HaCaT) for the expression of tissue-type plasminogen activator (tPA)-specific mRNA, as well as cell surface-associated and secreted tPA. Cells of early passages (passage no. 22) only expressed urokinase plasminogen activator (uPA)- but not tPA-specific mRNA. Cells after prolonged culture (passage no. 44) expressed uPA- and tPA-specific mRNA, but did not release tPA in the extracellular space and did not display surface-associated tPA. HaCaT cells transformed with the c-Ha-ras oncogene (HaCaTras) showed both secreted and surface-associated tPA antigen. The secreted and the surface-associated plasminogen activator (PA)-activity of HaCaTras cells were in part inhibitable by anticatalytic anti-tPA antibodies, thus indicating that tPA contributes to extracellular and surface-associated plasminogen activation. Finally, we demonstrate that tPA secretion of HaCaT 44 cells can be induced by retinoic acid, most likely via interaction of retinoic acid with nuclear-associated retinoic acid-receptor(s).

Plasminogen activation by human keratinocytes: molecular pathways and cell-biological consequences

Keratinocytes are the major cellular constituent of stratified epithelia. Defects in these epithelia are re-epithelialized by keratinocytes migrating from the edge of the defect into the wound. The cells form a monolayer with subsequent differentiation into a multilayered epithelium. It is thought that plasminogen activation by migrating keratinocytes is an important event during re-epithelialization. In the present report we summarize the studies on plasminogen activation by human keratinocytes in vitro and in vivo. Under the aspect of pericellular proteolysis the discussion is focused on the molecular mechanisms of plasminogen activation at the keratinocyte surface and on the cell-biological consequences of pericellular plasmin formation. We describe a cell surface-associated pathway of plasminogen activation which crucially depends on cell surface receptors for (pro)-uPA and plasmin(ogen). uPA bound to its receptor converts cell-bound plasminogen into the active protease plasmin. Compared to plasminogen activation in solution, activation at the keratinocyte cell surface is accelerated by a factor of approx. 7-10, and the plasmin generated and bound at the cell surface is protected against its specific inhibitor alpha 2-antiplasmin. Plasmin thus provided in the pericellular space leads to detachment of cultured keratinocytes from the growth substratum. Plasmin interferes with the adhesion of keratinocytes to fibrin, but not with the adhesion to collagen type I. By demonstrating that keratinocytes of the epithelial outgrowth in healing skin wounds express uPA and the uPA-R and that plasmin(ogen) is colocalized with uPA and/or uPA-R, indirect evidence is provided that this pathway may be operative in vivo. In view of previous findings that plasminogen activation is also observed under certain pathologic conditions in the epidermis, we conclude that plasminogen activation by keratinocytes is rather related to tissue damage and subsequent repair mechanisms than to a specific pathologic situation.

Expression of plasminogen activator enzymes in psoriatic epidermis

The plasminogen activators, tissue type and urokinase type (tPA and uPA, respectively) have been identified in human skin under normal conditions and in various inflammatory dermatoses, including psoriasis. By Northern blot analyses, mRNA for uPA, but not for tPA, has been previously identified in epidermal extracts from normal skin, whereas in psoriasis, mRNA for tPA is readily detected. To further characterize uPA and tPA expression in psoriasis, the localization of uPA and tPA mRNAs was evaluated by in situ hybridization. Studies were conducted using lesional and nonlesional skin of patients with psoriasis as well as normal skin. Additionally, in situ zymography using casein gel overlays was utilized to assess enzymatic activity. In psoriatic lesional skin, both uPA and tPA mRNAs were demonstrated by in situ hybridization. Message for tPA was observed throughout the epidermis with areas of accentuation in the superficial stratum spinosum. Message for uPA was more focal and was localized primarily in the basal layer. Zymography showed tPA activity was coordinately increased in psoriatic lesions. Uninvolved skin of psoriatic patients was similar to that of normal skin with respect to expression of plasminogen activators. In normal epidermis, neither tPA nor uPA mRNA could be detected by in situ hybridization. Activity for uPA, but not tPA, was observed by zymography. These studies suggest that alterations in plasminogen activators expression may contribute to the pathogenesis of psoriasis.

Vitamin D3 and calcipotriol decrease extracellular plasminogen activator activity in cultured keratinocytes

Vitamin D3, 1 alpha,25(OH)2D3, and its metabolites regulate the growth and differentiation of several cell types. Vitamin D3 and its analogue, calcipotriol (MC 903), inhibit the proliferation of cultured human and mouse keratinocytes and induce keratinocyte differentiation. Calcipotriol is effective in the treatment of psoriasis in which increased plasminogen activator activity has been reported. We analyzed therefore the effects of calcipotriol and vitamin D3 on the production of plasminogen activator (PA) activity in human keratinocytes and a mouse keratinocyte cell line. Caseinolysis-in-agarose assays indicated that vitamin D3 decreases total PA activity in both keratinocyte culture systems. Zymographic analyses of the medium indicated that the secreted activator was of the urokinase type (u-PA). A decrease was observed also in extracellular matrix and membrane-associated u-PA activity of vitamin D3 and calcipotriol treated cells. Immunoblotting analysis of the conditioned medium from human keratinocytes revealed a decrease in the u-PA protein levels. Accordingly, Northern hybridization analysis of the respective mRNAs indicated a rapid decrease in urokinase mRNA levels. Calcipotriol decreased u-PA activity also in the presence of inducers of u-PA activity like transforming growth factor-beta, epidermal growth factor, and phorbol-12-myristate-13-acetate. Calcipotriol also caused a decrease in tissue type PA (t-PA) activity of the keratinocytes. Most t-PA activity was associated with the extracellular matrices and cell membranes as revealed by zymographic analysis. Paradoxically, the secretion and deposition of the matrix of plasminogen activator inhibitor type 1 decreased in calcipotriol-treated cells. The results indicate that a major effect of vitamin D3 on cultured keratinocytes is a decrease of plasminogen activator activity.

Keratinocyte growth factor (FGF-7) stimulates migration and plasminogen activator activity of normal human keratinocytes

Keratinocyte growth factor (KGF), a member of the fibroblast growth factor (FGF) family (and alternatively designated FGF-7), is a paracrine growth factor produced by mesenchymal cells and mitogenic specifically for epithelial cells. The potential effect of KGF on wound healing was assessed in vitro by measuring randomized migration and plasminogen activator (PA) activity of keratinocytes in response to the growth factor. Incubation of normal human keratinocytes with KGF in modified MCDB 153 medium significantly stimulated cell migration and PA activity compared with control (p < 0.001 and p < 0.01, respectively). When tested in these assays on an equimolar basis, 1 nM KGF was at least as potent as transforming growth factor alpha and more active than basic FGF. None of these effects were observed when KGF was administered to fibroblasts or endothelial cells. Stimulation of keratinocyte migration by KGF was dose dependent, and a neutralizing monoclonal antibody against KGF reduced KGF-stimulated migration and cell growth. Zymographic analyses of cell extracts and conditioned medium from KGF-treated keratinocytes revealed increased PA activity, which was mainly attributable to an elevated level of urokinase-type PA. These in vitro results suggest that KGF may have an important role in stimulating reepithelialization during the process of wound repair.

Immunohistochemical characterization of the plasminogen activator system in psoriatic epidermis

The relative topographical distribution of urokinase-type plasminogen activator (uPA), tissue-type PA (tPA), PA-inhibitor-1 (PAI-1), PA-inhibitor-2 (PAI-2), plasmin(ogen), alpha 2-antiplasmin, and alpha 2-macroglobulin was studied in lesional epidermis of psoriasis vulgaris, and in normal epidermis, by immunohistochemistry. In psoriatic epidermis, tPA predominated, although uPA was found in some biopsies. PAs were not detected in normal epidermis. PAI-1 was not detected in normal epidermis and was only present in a proportion of biopsies of psoriatic lesions. PAI-2 was found in normal and psoriatic epidermis. Plasmin(ogen) was confined to the basal cell layer of normal epidermis, whereas in lesional psoriatic skin it was scattered throughout the epidermis. Alpha 2-antiplasmin and alpha 2-macroglobulin were not found in the epidermis of normal skin. In psoriatic epidermis alpha 2-antiplasmin was confined to the subcorneal layer, whereas staining for alpha 2-macroglobulin was found only in a proportion of biopsies, in the upper epidermis. Our immunohistological findings indicate that colocalization of tPA and its substrate plasminogen may allow efficient generation of plasmin, and that the focal absence of plasmin inhibitors may then favour the persistence of plasmin activity.

Autocrine/paracrine regulation of keratinocyte urokinase plasminogen activator through the TGF-alpha/EGF receptor

Transforming growth factor-alpha (TGF-alpha) appears to be an important autocrine/paracrine regulator of keratinocyte function. Not only does TGF-alpha induce keratinocyte proliferation and migration in vitro, but it also has been detected in normal human epidermis and at elevated levels in hyperproliferative epidermis. In the present study we report that exogenous TGF-alpha increases urokinase-type plasminogen activator (uPA) in cultured human keratinocytes. Furthermore, in the absence of exogenous growth factors, the "basal" levels of uPA are decreased by an antagonist monoclonal antibody to the receptor shared by TGF-alpha and epidermal growth factor (EGF). These results suggest that an endogenous factor serves as an autocrine/paracrine regulator of keratinocyte uPA. We hypothesize that activation of the TGF-alpha/EGF receptor may coordinately regulate the keratinocyte response to cutaneous wounding, which includes enhanced uPA expression, migration, and proliferation.

An immunohistochemical study of the distribution of plasminogen and plasminogen activators in bullous pemphigoid

Abnormalities of the cutaneous plasminogen/plasminogen activator system have been associated with acantholytic disorders, psoriasis, keratinocytes in culture, and epidermis in healing wounds. The present study was undertaken to investigate the possible role of the plasmin/plasminogen protease system in lesion development in bullous pemphigoid (BP). Using polyclonal antibodies and a fluorescent technique, the immunohistochemical distribution of plasmin/plasminogen, fibrinogen and the plasminogen activators, urokinase (uPA) and tissue plasminogen activator (tPA), were studied in lesional and non-lesional skin from nine BP patients, one with linear IgA disease (LAD) and one with pemphigoid gestationis (PG). The distribution of the proteases was compared with that in normal skin (n = 4) and in suction blisters (n = 2). In normal skin, fibrinogen, tPA and uPA were absent from the epidermis and plasminogen was confined to the basal layer. Uninvolved BP skin was identical to controls. Focal areas of suprabasal plasminogen expression in the region of a blister was seen in 3/9 BP lesions and in 1/2 suction blisters. In 6/9 BP lesions and both uninvolved and lesional LAD and PG skin were identical to controls, and no suprabasal expression of plasminogen was present. These findings suggest that suprabasal plasminogen expression is unlikely to play a fundamental role in the pathogenesis of blister formation in BP as enhanced expression was not present in every case and the finding was not specific to BP, also occurring in a suction blister. Enhanced plasminogen expression rather may be a reflection of the processes of tissue repair.

Plasminogen activation in lesional skin of Pemphigus vulgaris type Neumann

Zymographic and immunological studies revealed that primarily tissue-type plasminogen activator and to a lesser extent urokinase-type plasminogen activator were present in fluids of pemphigus vulgaris (type Neumann) skin blisters. Furthermore, plasmin activity was detected in pemphigus blister fluids using chromogenic peptide substrate assays. In pemphigus, but not in control, suction blister fluids plasmin/alpha 2-antiplasmin and plasmin/alpha 2-macroglobulin complexes were found by immunoprecipitation or by testing in immunoassays after fractionation by molecular-sieve chromatography. Plasmin activity, detected by a low molecular weight chromogenic peptide assay, was ascribed to plasmin/alpha 2-macroglobulin complexes. Since formation of plasmin/inhibitor complexes requires active plasmin, the finding indicates previous activation of plasminogen in pemphigus lesions.

Regulation of urokinase plasminogen activator localization in keratinocytes by calcium ion and E-cadherin

In keratinocyte culture, the cellular distribution of many adhesion markers and the organization of intercellular junctions are controlled by the calcium ion concentration of the medium. We show in the present study that urokinase plasminogen activator (uPA) localization in the human keratinocyte is similarly dependent upon calcium concentration. At 30 microM calcium, uPA is present throughout the cell, often with a perinuclear concentration. Upon calcium elevation to 1.0 mM, uPA is concentrated along the cell-cell borders, where it colocalizes (at the light microscope level) with E-cadherin. Blocking antibody to E-cadherin delays the calcium-induced redistribution of uPA, in a manner very similar to the previously observed delay in redistribution of several adhesion-related markers, including vinculin, desmoplakin, and beta 1 integrin. These data suggest a link between the redistribution of uPA to the cell-cell borders and the calcium-induced organization of intercellular junctions in the human keratinocyte. The presence of uPA along the intercellular borders suggests that this enzyme may be involved in regulation of epidermal adhesion through proteolysis.

Enhanced association of plasminogen/plasmin with lesional epidermis of bullous pemphigoid

The distribution of plasminogen/plasmin, the central proteolytic component of the plasminogen activator/plasmin system was analysed in lesional skin of bullous pemphigoid by using monoclonal antibodies (MAbs) specific for distinct epitopes of the plasminogen/plasmin molecule. Four groups of MAbs were used: (i) MAbs HD-PG 1 and HD-PG 2, specific for epitopes associated with the lysine-binding sites I (kringle domain 1 + 2 + 3) and II (kringle domain 4) of plasminogen/plasmin, (ii) MAbs HD-PG 6 and HD-PG 7, specific for the lysine binding site I only, (iii) MAbs HD-PG 12 (formerly designated P 2) and HD-PG 18, specific for non-kringle domains of glu- and lys-plasminogen, and (iv) MAb HD-PG 13 which recognizes glu-plasminogen, only. The basal cell layers of normal skin consistently reacted with MAb HD-PG 12, whereas only faint staining was seen with the other MAbs in the same biopsies. In contrast, all anti-plasminogen/plasmin MAbs strongly stained lower and intermediate epidermal cell layers of fully developed bullous pemphigoid lesions.

Urokinase plasminogen activator is immunocytochemically detectable in squamous cell but not basal cell carcinomas

The presence of plasminogen activators (PA) in a variety of solid tumors appears to correlate, in a number of instances, with enhanced invasive or metastatic capabilities. In the present study, we have immunocytochemically examined basal cell (BCC) and squamous cell carcinomas (SCC) comprising a spectrum of histologic subtypes for the presence of urokinase-type (uPA) and tissue-type (tPA) PA. Neither uPA nor tPA was noted in any BCC, whether of the nodular, infiltrative, morpheaform, or basosquamous variety. uPA but not tPA was seen in 12 of 16 SCC examined; the tumors lacking uPA were all histologically well differentiated. No relationship between uPA expression and depth of invasion was noted, and uPA was not preferentially expressed at tumor borders. We conclude that uPA presence in SCC may relate to the degree of differentiation.

Plasminogen binding sites in normal human skin

Plasminogen is detected in the basal cell layer of the epidermis, keratinocytes can generate plasminogen activators and it is suggested that the generation of plasmin may facilitate keratinocyte division, migration and differentiation. In this study we have investigated the characteristics of plasminogen binding sites in normal human epidermis. It was found that 6-aminohexanoic acid and benzamidine displaced endogenous epidermal plasminogen from the basal layer suggesting that endogenous plasminogen binds initially via the kringle 5 aminohexyl (AH) site. Plasminogen binding sites in epidermis were further investigated by displacing endogenous plasminogen and incubating sections with exogenously added glu-plasminogen, lys-plasminogen and plasmin or the isolated plasminogen fragments kringles 1-3, kringle 4 and kringle 5L. The results suggest that the uptake of plasminogen involves primary interaction with the kringle 5AH site and a secondary interaction with lysine binding sites of kringles 1-3. Cell binding is not dependent upon additional reactions of the plasmin active centre.

Cell adhesion in Hailey-Hailey disease and Darier's disease: immunocytological and explant-tissue-culture studies

The pathogenesis of Hailey-Hailey disease and Darier's disease was investigated using immunocytological and explant-tissue-culture techniques. There was breakdown of the intercellular adhesions between keratinocytes in explants from clinically uninvolved skin of patients with Hailey-Hailey disease or Darier's disease. The major desmosomal components were present in the cultures and were expressed in a punctate peripheral pattern at cell-cell contact sites, but there was diffuse staining of acantholytic cells. Plasminogen, which is expressed by basal keratinocytes in normal skin, was detected in association with suprabasal acantholytic cells in skin biopsies from these diseases. Plasminogen was reversibly displaced from the cells by 6-aminohexanoic acid, suggesting that binding is mediated by a reaction with the lysine receptor on the plasminogen molecule. Plasminogen was also detected in separating cells in explant cultures and there was cytoplasmic expression of the plasminogen activator urokinase by these cells. These abnormalities are not unique to either disease and do not account for the phenotypic differences between Darier's disease and Hailey-Hailey disease, but plasmin generation may have a role in perpetuating cell separation.

Induction of HLA-DR by interferon-gamma requires a trypsin-like protease

Induction of HLA-DR antigen expression by interferon-gamma (IFN-gamma) is inhibited by trypsin inhibitors and an anti-trypsin monoclonal antibody, but not by chymotrypsin inhibitors, suggesting a requirement for trypsin-like protease (TLP) activity in IFN-gamma-induced HLA-DR expression. Using p-nitroanilide and thioester substrates, TLP activity was demonstrated in cellular extracts of a hybrid epidermal cell line and judged to be essential for HLA-DR expression. TLP activity was inhibited by the trypsin inhibitors soybean trypsin inhibitor, ovomucoid trypsin inhibitor, and tosyl-lysyl-chloromethyl ketone and by an anti-trypsin monoclonal antibody, closely paralleling inhibition of HLA-DR expression by such agents. TLP activity was enhanced by exposure to trypsin-linked agarose, indicating that the protease normally exists in an inactive form, perhaps in an enzyme-inhibitor complex or as an activatable proenzyme. Finding glucocorticoids (GC) to also inhibit IFN-gamma-induced HLA-DR expression and to regulate serine protease, especially urokinase plasminogen activator (uPA), activity raised the possibility of GC regulation of TLP activity. However, TLP activity was found to be constitutively expressed, regulated by neither GC nor IFN-gamma, nor was uPA activity involved in HLA-DR regulation. Trypsin inhibitors and GC also inhibited induction of intracellular 2',5'-oligoadenylate (2-5A) synthetase by IFN-gamma. Thus, TLP activity is required for IFN-gamma induction of HLA-DR and 2-5A synthetase.

mRNA for tissue-type plasminogen activator is present in lesional epidermis from patients with psoriasis, pemphigus, or bullous pemphigoid, but is not detected in normal epidermis

Plasminogen activator (PA), which catalyzes the conversion of plasminogen to the proteinase plasmin, has been implicated in a variety of cutaneous disorders. Lesional epidermis from patients with psoriasis, pemphigus, bullous pemphigoid, and Hailey-Hailey disease contains elevated levels of tissue-type PA (tPA) activity compared to non-lesional epidermis or to epidermis from normal individuals. In the present study, we have used Northern blot analysis to demonstrate that mRNA for tPA is detectable in lesions from patients with psoriasis, pemphigus, and bullous pemphigoid, but is not detectable in normal epidermis. These data strongly suggest that the tPA enzymatic activity present in lesional epidermis results from enhanced synthesis of the enzyme in situ, secondary to elevated steady-state levels of tPA mRNA. Cultured keratinocytes likewise are shown to contain tPA mRNA. Previous investigators have suggested that the phenotypes of keratinocytes in culture, psoriatic epidermis, and epidermis in the process of wound reepithelialization are comparable. Our findings, combined with those of other investigators, suggest that elevated tPA expression may be another common feature of epidermis under these circumstances.

A high-affinity receptor for urokinase plasminogen activator on human keratinocytes: characterization and potential modulation during migration

Low passage cultures of normal human keratinocytes produce several components of the plasminogen activator/plasmin proteolytic cascade, including urokinase plasminogen activator (uPA), tissue plasminogen activator (tPA), and two specific inhibitors. Studies here presented demonstrate that these cells also contain a high-affinity (Kd = 3 x 10(-10) M) plasma membrane-binding site for uPA. High molecular weight uPA, either as the single-chain precursor or two-chain activated form, bound to the receptor; however, low molecular weight (33 kD) uPA, tPA, or epidermal growth factor did not compete for binding, demonstrating specificity. Acid treatment, which removed endogenous uPA from the receptor, was required to detect maximal binding (45,000 sites per cell). To investigate the possibility that the uPA receptor on keratinocytes may be involved in epithelial migration during wound repair, cultures were wounded and allowed to migrate into the wounded site. Binding sites for uPA were localized by autoradiographic analysis of 125I-uPA binding as well as by immunocytochemical studies using anti-uPA IgG. With both techniques uPA binding sites were detected selectively on the plasma membrane of cells at the leading edge of the migrating epithelial sheet. This localization pattern suggests that uPA receptor expression on keratinocytes may be coupled to cell migration during cutaneous wounding.