Phorbol Diesters Regulate Expression of the Membrane Neutral Metalloendopeptidase (EC 3.4.24.11) in Rabbit Synovial Fibroblasts and Mammary Epithelial Cells

Activity and expression of enkephalinase and aminopeptidase N in regions of the mesocorticolimbic system are selectively modified by acute ethanol administration

Opioid peptides play a key role in ethanol reinforcement and alcohol drinking behavior. However, regulation of opioid levels by peptidase-degrading activities in ethanol's actions in brain is still unclear. The aim of this work was to study the acute effects of ethanol (2.5 g/kg) on enkephalinase (NEP) and aminopeptidase N (APN) activities and expression in regions of the mesocorticolimbic system, as well as on corticosterone levels in serum for up to 24 h after administration. Enzymatic activities were measured by fluorometric assays, mRNA's expression by reverse transcriptase polymerase chain reaction (RT-PCR) and corticosterone levels by radioimmunoassay. Acute ethanol administration modified peptidase activity and expression with different kinetics. Ethanol induced a transitory increase and decrease in NEP and APN activities in the frontal cortex (FC) and ventral tegmental area (VTA), whereas only increases in these activities were observed in the nucleus accumbens (NAcc). Ethanol induced an increase in NEP mRNA in the FC and decreases in APN mRNA in the FC and NAcc. In contrast, ethanol produced biphasic effects on both enzymes expression in the VTA. Corticosterone levels were not changed by ethanol. Our results suggest that NEP and APN could play a main role in ethanol reinforcement through regulation of opioid levels in mesolimbic areas.

CD10 Expression in Pure Stromal and Sex Cord-Stromal Tumors of the Ovary

CD10 has been recently advocated as a good immunohistochemical marker for endometrial stromal tumors. Metastatic endometrial stromal tumors to the ovary and primary endometrioid stromal sarcomas may show overlapping histological features with pure stromal and sex cord-stromal tumors (SCSTs). We investigated CD10 expression in a large series of pure stromal and SCSTs of the ovary to ascertain whether CD10 may aid in this differential diagnosis. Archival material from 11 fibromas, 10 thecomas, 10 sclerosing stromal tumors (SSTs), 10 adult granulosa cell tumors (AGCTs), 4 luteinized AGCTs, 9 juvenile granulosa cell tumors (JGCTs), 9 Sertoli cell tumors, 9 Sertoli-Leydig cell tumors, 11 sex cord tumors with annular tubules, 10 steroid cell tumors (StCTs), and 8 fibrosarcomas of the ovary were immunostained for CD10. The percentage of cells stained (<5%, 5%-39%, 40%-75%, and >75%) and intensity of staining (1+, 2+, 3+) were evaluated. CD10 was expressed in 7 of 10 thecomas (4 with 5%-75% and mostly 1+), 9 of 10 SSTs (7 with 5%-39% + cells, mostly 1+), 9 of 10 AGCTs (<5%-39%, four 1+, five 2+), 1 of 4 luteinized AGCTs (<5% and 1+), 8 of 9 JGCTs (mostly <5% to 39% and +1), 4 of 9 Sertoli cell tumors (either focal or >75% with variable intensity), 4 of 9 Sertoli-Leydig cell tumors (mostly <10% with variable staining), with the Leydig cells being positive in only 1 tumor (1+ and <5%), and 7 of 10 StCTs (4 tumors with more than 75% + cells, from 1+ to 3+). All fibromas, all but 1 fibrosarcoma (<5% and 1+), and all sex cord tumors with annular tubules were CD10 negative. CD10 expression was frequently seen in StCTs, SSTs, and thecomas of the ovary, although the latter 2 categories usually showed only faint immunoreactivity. In conclusion the frequency and intensity of CD10 immunoreactivity in pure stromal and sex cord-stromal ovarian tumors are low and contrast with the typical strong and diffuse immunostaining seen in endometrial stromal tumors; however, faint CD10 positivity is consistent with the diagnosis of ovarian SCST. Steroid cell tumors are often positive for CD10, but these tumors do not pose problems in differential diagnosis with endometrial stromal tumors. CD10 may play a useful role in aiding the differential between endometrial stromal tumors in the ovary and SCST and stromal tumors.

Induction of neutral endopeptidase activity in PC-3 cells by an aqueous extract of Epilobium angustifolium L. and oenothein B

An aqueous extract of Epilobium angustifolium and its main compound oenothein B (OeB), a dimeric macrocyclic ellagitannin, are specifically able to induce the neutral endopeptidase (NEP) in prostate cancer cells. The angiotensin-converting enzyme (ACE) is not influenced. Additionally, a weak but statistically significant inhibition of cell proliferation is observed. Simultaneous treatment of the cells with arabinosylcytosine and the extract as well as the OeB, leads to an additional enhancement of NEP activity. Taking into account the role of this peptidase in prostate cancer progression, our results might offer a pharmacological explanation for the use of Epilobium in folk medicine.

Alphavbeta6-Fyn signaling promotes oral cancer progression

We have previously shown that the integrin beta6 is neo-expressed in invasive oral squamous cell carcinoma (SCC) and is correlated with oral tumor progression. However, the mechanism by which the integrin beta6 promotes oral tumor progression is not well understood. The purpose of the present study was to determine whether integrin beta6 signaling activates Fyn and thus promotes oral squamous cell carcinoma progression. We analyzed the integrin beta6 signaling complex and investigated the function of these signaling molecules in oral SCC cells. We found that, upon ligation of the integrin beta6 with fibronectin, beta6 complexed with Fyn and activated it. The activation of Fyn recruited and activated focal adhesion kinase to this complex. This complex was necessary to activate Shc and to couple beta6 signaling to the Raf-ERK/MAPK pathway. This pathway transcriptionally activated the matrix metalloproteinase-3 gene and promoted oral SCC cell proliferation and experimental metastasis in vivo. These findings indicate that integrin beta6 signaling activates Fyn and thus promotes oral cancer progression.

Transcriptional regulation of stromelysin-1 gene expression is altered during progression of mouse mammary epithelial cells from functionally normal to malignant

The matrix metalloproteinase stromelysin-1 plays a central role during mammary gland development and tumor progression. To gain insight into the regulation of stromelysin-1 gene expression, the murine stromelysin-1 promoter was cloned and transfected into mouse mammary epithelial cells displaying various degrees of malignancy. A reconstituted basement membrane inhibited stromelysin-1 promoter activity in functionally normal cells, had little effect on moderately malignant cells and up-regulated the promoter in highly malignant cells. Spreading of normal and malignant cells was reduced by a reconstituted basement membrane, compared to a plastic substratum. Preventing spreading by maintenance of cells in suspension culture, regulated stromelysin-1 promoter activity in a manner similar to that on a reconstituted basement membrane. Conversely, increasing spreading by augmenting substratum adhesivity up-regulated stromelysin-1 promoter activity in tumor cells. In cells with reduced spreading in the presence of reconstituted basement membrane and in suspension culture, actin stress fibers were replaced by cortical actin bundles. In tumor cells, but not in functionally normal cells, treatment with phorbol diesters also resulted in accumulation of cortical actin and increased stromelysin-1 promoter activity. Consistent with an epithelial-to-mesenchymal conversion, regulation of stromelysin-1 gene expression in highly malignant cells was similar to its regulation in mammary fibroblasts. We conclude that the switch in transcriptional regulation of stromelysin-1 expression that occurs during epithelial-to-mesenchymal transition and conversion to tumorigenicity is related to altered regulation of signals from the cytoarchitecture.

Differential expression of the Kell blood group and CD10 antigens: two related membrane metallopeptidases during differentiation of K562 cells by phorbol ester and hemin

The erythroleukemic cell line K562 can undergo further differentiation in erythroid or megakaryocytic lineage depending on the nature of the stimulus. Phorbol ester (PMA) stimulates megakaryocytic development whereas hemin promotes erythroid differentiation of these cells. We have examined the effect of PMA and hemin on the expression of the Kell blood group and CD10 antigens, two related proteins that belong to a family of membrane-bound neutral metalloendopeptidases. We show here that differentiation of K562 cells by PMA in the megakaryocytic lineage results in abolishment of Kell mRNA accumulation and protein expression and, in parallel, the induction of CD10 mRNA accumulation, protein expression, and enzymatic activity. Conversely, differentiation of these cells by hemin in the erythroid lineage is accompanied by an up-regulation of Kell mRNA and protein expression, with no changes in CD10 mRNA and protein expression. Thus, CD10 and Kell can be regarded as specific markers of the differentiation of K562 cells in the megakaryocytic and erythroid lineages, respectively.

Gene expression and activity of specific opioid-degrading enzymes in different brain regions of the AA and ANA lines of rats

There is increasing evidence that alcoholism runs in families suggesting that genetic factors may play a role. In support of this hypothesis, the alcohol-preferring (AA) and the alcohol-avoiding (ANA) rat lines have been developed through selective outbreeding. Numerous studies indicate that the endogenous opioid system may be involved in controlling ethanol consumption. Changes in opioid peptides and opioid receptors have been described after ethanol intake. But, the influence of ethanol on peptidolytic degradation of opioid peptides has been largely ignored, although the peptidase-mediated metabolism of neuropeptides is known as an important regulatory site of peptidergic transmission. Neutral endopeptidase 24.11 (NEP) and angiotensin-converting enzyme (ACE) degrade neuropeptides, including enkephalin and are expressed in the brain. Furthermore, a good correspondence between the regional distribution of NEP and opioid receptors in rat brain has already been reported pointing to a possible role of NEP in regulating opioid peptides. For both enzymes studied, the gene expression pattern was found to be in good agreement with the corresponding enzyme activities in the brain regions investigated, showing the highest levels for both specific mRNAs and enzyme activities in the striatum. Differences in both measured parameters were detected in distinct brain regions of AA and ANA rats. Furthermore, in some brain regions discrepancies between ACE and NEP mRNA levels and the corresponding enzyme activities were observed. For example, in olfactory bulb and striatum such discrepancies were found for both enzymes studied. In tegmentum/colliculi a higher NEP gene expression in AA rats was associated with a higher NEP enzyme activity compared to the amounts found in ANA rats.

Neuropeptides in the skin: interactions between the neuroendocrine and the skin immune systems

The interaction between components of the nervous system and multiple target cells in the cutaneous immune system has been receiving increasing attention. It has been observed that certain skin diseases such as psoriasis and atopic dermatitis have a neurogenic component. Neuropeptides released by sensory nerves that innervate the skin and often contact epidermal and dermal cells can directly modulate functions of keratinocytes, Langerhans cells (LC), mast cells, dermal microvascular endothelial cells and infiltrating immune cells. Among these neuropeptides the tachykinins substance P (SP) and neurokinin A (NKA), calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and somatostatin (SOM) have been reported to effectively modulate skin and immune cell functions such as cell proliferation, cytokine production or antigen presentation under physiological or pathophysiological conditions. Expression and regulation of their corresponding receptors that are expressed on a variety of skin cells as well as the presence of neuropeptide-specific peptidases such as neutral endopeptidase (NEP) or angiotensin-converting enzyme (ACE) determine the final biological response mediated by these peptides on the target cell or tissue. Likewise, skin cells like keratinocytes or fibroblasts are a source for neurotrophins such as nerve growth factor that are required not only for survival and regeneration of sensory neurons but also to control responsiveness of these neurons to external stimuli. Therefore, neuropeptides, neuropeptide receptors, neuropeptide-degrading enzymes and neurotrophins participate in a complex, interdependent network of mediators that modulate skin inflammation, wound healing and the skin immune system. This review will focus on recent studies demonstrating the role of tachykinins, CGRP, SOM and VIP and their receptors and neuropeptide-degrading enzymes in mediating neurogenic inflammation in the skin.

The Type 2 CD10/Neutral Endopeptidase 24.11 Promoter: Functional Characterization and Tissue-Specific Regulation by CBF/NF-Y Isoforms

The cell surface zinc metalloproteinase CD10/neutral endopeptidase 24.11 ([NEP] neprilysin) functions as part of a regulatory loop to control local concentrations of peptide substrates and associated peptide-mediated signal transduction. The physiologic role of the enzyme depends on available substrates in specific organs and cell types. Although CD10/NEP is expressed on a restricted subset of normal and malignant lymphoid progenitors, the enzyme is also expressed by a variety of epithelial cells. To explore the mechanism of tissue-specific expression of this regulatory enzyme, we characterized the major (type 2) CD10/NEP promoter and identified three functionally active transcription factor binding sites (regions I to III). CBF/NF-Y binds to the inverted CCAAT box in region I, whereas a second positive and a third negative factor bind to regions II and III, respectively. Although region I is required for maximal CD10/NEP-driven luciferase activity in the examined epithelial cell lines, this region is not required for maximal activity in the evaluated lymphoid cell lines. The apparent tissue-specific differences in requirements for region I (and CBF/NF-Y) are of particular interest because lymphoid and epithelial cells express alternatively spliced versions of CBF/NF-Y that differ in biologic activity.

Simian virus 40 transformation alters the actin cytoskeleton, expression of matrix metalloproteinases and inhibitors of metalloproteinases, and invasive behavior of normal and ataxia-telangiectasia human skin fibroblasts

Alterations in the actin cytoskeleton of normal cells result in changes in cell shape and adhesiveness and induce expression of matrix-degrading matrix metalloproteinases. We examined the effect of simian virus 40 transformation of normal and ataxia-telangiectasia human skin fibroblasts, a process that produces actin reorganization, altered cell morphology, and altered cell behavior, on expression of genes of the matrix metalloproteinase and tissue inhibitor of metalloproteinases gene families. Simian virus 40 transformation induced collagenase-1 gene expression; in contrast, stromelysin-1, 72-kDa gelatinase (gelatinase A), tissue inhibitor of metalloproteinases-1, and tissue inhibitor of metalloproteinases-2 genes were repressed. Transformation also altered the response of the fibroblasts to 12-O-tetradecanoylphorbol-13-acetate. Collagenase mRNA was induced in 12-O-tetradecanoylphorbol-13-acetate treated transformed cells up to 50-fold more than in untreated transformed cells or in 12-O-tetradecanoylphorbol-13-acetate treated untransformed parent cells. In contrast, 12-O-tetradecanoylphorbol-13-acetate did not overcome the attenuated expression of stromelysin-1 in the simian virus 40 transformants. In addition, 92-kDa gelatinase (gelatinase B) was induced by 12-O-tetradecanoylphorbol-13-acetate only in the simian virus 40 transformants. The responses of gelatinase A and tissue inhibitor of metalloproteinases-1 to 12-O-tetradecanoylphorbol-13-acetate were unchanged. The pattern of altered proteinase expression after transformation was accompanied by a phenotypic alteration in cell invasion. The simian virus 40 transformants exhibited enhanced invasiveness through a basement-membrane-like matrix. These data demonstrate that enhanced invasiveness in simian virus 40 transformed cells is accompanied by changes in actin organization and expression of proteinases and inhibitors, as well as in the balance between proteinases and inhibitors in favor of proteinases.

Tissue-specific expression of rat neutral endopeptidase (neprilysin) mRNAs

Neutral endopeptidase is a cell surface zinc metal-lopeptidase that regulates the action of a variety of physiologically active peptides. The enzyme exhibits a wide tissue distribution, being most abundant in kidney and lung. Three rat neutral endopeptidase cDNAs with unique 5'-untranslated sequences were isolated. Distribution of the corresponding mRNAs in rat tissues was analyzed by RNase protection assays and by in situ hybridization. In kidney, the type 2b transcript was the major species. In lung and testis, type 1 and type 2b transcripts were expressed in approximately equal amounts, while in brain and spinal cord the type 1 mRNA was the major transcript. These findings were extended by in situ hybridization studies. All three mRNAs were expressed in the proximal tubule of the kidney, with the type 2b transcript giving the strongest signal. In the frontoparietal cortex, expression of the neutral endopeptidase mRNA subtypes was cell- and region-specific. The type 1 transcript was localized to neurons, type 2b mRNA was not detectable, while type 3 mRNA was localized to the oligodendrocytes of the corpus callosum. These results clearly demonstrate that expression of the three neutral endopeptidase mRNAs can be regulated in a cell-specific manner.

Activation of adenylate cyclase and phosphodiesterase inhibition enhance neutral endopeptidase activity in human endothelial cells

Endothelial neutral endopeptidase (EC 3.4.24.11, NEP) contributes to the inactivation of vasoactive and inflammatory peptides such as f-Met-Leu-Phe, substance P, atrial natriuretic peptide, and bradykinin. The aim of the present study was to investigate the cellular regulation of NEP expression in human endothelial cells, focusing on the role of cyclic nucleotides and cellular phosphodiesterases (PDE). Activation of adenylate cyclase by forskolin or prostaglandin E1 (PGE1) induced an increase of NEP activity and NEP protein after 24 h of incubation. This effect was mimicked by two activators of protein kinase A, dibutyryl-cAMP and 8-bromo-cAMP. The nonspecific PDE inhibitor, 3-isobutyl-1-methylxanthine (200 microM), increased NEP activity up to 192%. The activator of guanylate cyclase, sodium nitroprusside (SNP), did not affect NEP activity but completely inhibited the 3-isobutyl-1-methylxanthine-mediated increase of NEP activity. The PDE-III inhibitors motapizone (100 microM) and enoximone (100 microM) enhanced NEP activity up to 188% and 213%, the PDE-IV inhibitor rolipram (3 microM) up to 162%, and the combined PDE-III/IV inhibitor zardaverine (1 microM) up to 176% of control values. The present data provide evidence for a cAMP-mediated increase of NEP activity in human endothelial cells.

Ectoenzyme regulation by phenotypically distinct fibroblast sub-populations isolated from the human mammary gland

Inter- and intralobular mammary fibroblasts have been separated from normal human breast tissue and cultured to study the differential expression of ectoenzymes present within the stroma of the normal gland and associated with breast cancers. Specific ectoenzymes were identified by indirect immunofluorescence and quantified by flow cytometry and semi-quantitative PCR. A consistent difference was noted between the two fibroblast sub-populations at early passage in respect of dipeptidyl peptidase IV (DPP IV) and aminopeptidase N (APN) expression. Early passage intralobular fibroblasts were positive for APN but negative for DPP IV, as seen in the intact tissue. However, with continued sub-culture they gradually began to express DPP IV, until at later passages they became indistinguishable from the interlobular fibroblasts, which were APN and DPP IV-positive at all stages in culture, as they are in intact tissue. Neutral endopeptidase (NEP/CALLA/CD10) is not expressed by normal adult breast fibroblasts but is found in the stroma associated with over 60% of breast cancers. It was up-regulated in vitro on both inter- and intralobular fibroblasts, with final levels that were significantly (&lt; 14 times) higher on the former in all pairs of preparations from individual donors analysed. This difference persisted with continued passage, and levels of the ectoenzyme and its messenger RNA were further up-regulated by hydrocortisone in both populations. These results demonstrate that phenotypically distinct cultures of human mammary fibroblast sub-populations can be used to study the regulation of these stromal ectoenzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased gelatinolytic and caseinolytic activity in the thermally injured, nutritionally compromised rat cornea: detection of a 27-kDa lymphoreticular cell-associated caseinase

This study assesses the impact of various forms of injury on matrix degrading enzymes in nutritionally compromised rat corneas. In vitamin A-deficient (nutritionally compromised) and normal control corneas, in vivo or ex vivo mild mechanical abrasion did not appreciably alter the activity of either the 65-kDa or the 92-kDa gelatinases. In contrast, after thermal injury, while no appreciable change was detected in activity associated with the 65-kDa gelatinase in either vitamin A-deficient or normal control corneas, 92-kDa gelatinolytic activity was consistently higher in corneas from both groups, although activity associated with nutritionally compromised corneas was much higher. In these corneas, thermal injury also induced the expression of two high molecular weight (approximately 130-kDa and 225-kDa) gelatinases and a 27-kDa caseinase. While gelatinases were totally inactivated by inhibitors of metalloproteinases such as 1,10-phenanthroline and Galardin MPI, the 27-kDa caseinase showed considerable susceptibility to a mixture of serine protease inhibitors (aprotinin, dichloro-isocoumarin and pA-PMSF [(4-amidino-phenyl)-methane-sulphonyl fluoride]. Furthermore, unactivated-lymphoreticular cells from either nutritionally compromised or normal control animals contained a 24- and 27-kDa caseinase, however most of the activity was due to the 24-kDa caseinase. In contrast, glycogen-activated lymphoreticular cells contained a preponderance of the 27-kDa caseinase. Activated-lymphoreticular cells also expressed 92-kDa, 130-kDa and 225-kDa gelatinases. The presence of low molecular weight caseinases in lymphoreticular cells implicates them as the source of these enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

The expression of matrix metalloproteinases and their inhibitors by pig synovial cells and their regulation by combinations of cytokines and growth factors

1. Pig synovial fibroblasts in culture were studied to determine if they were an easily reproducible model system for studying the actions of cytokines and growth factors on human synovial cells. The biochemical analyses were conducted by activity assays, enzymography and Northern blot. 2. Human recombinant interleukin-1 alpha, basic fibroblast growth factor and transforming growth factor-beta 1 were studied in combinations because of their known involvement in controlling tissue remodelling. 3. The response of pig fibroblasts to these agents, in terms of the expression of matrix metalloproteinases (collagenase, gelatinase and stromelysin) and their inhibitors (TIMPs), show that they behave similarly enough to human cells for use when supplies of human primary cells are unavailable.

Effects of bombesin and gastrin-releasing peptide on human bronchial epithelial cells from a series of donors: individual variation and modulation by bombesin analogs

Human pulmonary neuroendocrine cells produce a variety of hormones, including mammalian bombesin (BN) or gastrin-releasing peptide (GRP). Neuroendocrine cell hyperplasia and increased release of BN-like peptides occur in several diseases of the airways, including chronic obstructive pulmonary disease (COPD) and bronchopulmonary dysplasia. Growth stimulation of human bronchial epithelial cells by BN, as measured in a colony-forming assay, has been reported previously (Willey et al.:Exp. Cell Res. 153:245-248, 1984). In a follow-up to this report, we examined the response of human bronchial epithelial (HBE) cells to BN or GRP in a similar system, using cells derived from 13 human tissue donors. A stimulatory response (increased colony-forming efficiency) was found in cultures from 8 donors, including 3 with COPD. Statistical significance was found for the data from 5 of these 8 donors. The other 5 donors, 1 normal and 4 lung cancer patients, showed inhibition of colony formation by BN or GRP. Statistical significance was found for 3 of these donors. The ability of BN analogs to modulate BN stimulation was examined in cells from a donor with COPD. [psi Leu13,Leu14] BN(1-14), a BN antagonist, blocked the stimulation induced by BN. [D-Cpa6,psi Leu13,Phe14] BN(6-14), a mixed agonist-antagonist, showed partial agonist activity in HBE cells. [D-Phe1,Leu8,9] Litorin, an agonist, also showed agonist activity in a colony-forming assay with cells from these donors. These results indicate that responsiveness to BN/GRP may vary widely in the human population. Responsiveness may be heightened in disease states involving a proliferation of neuroendocrine cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Increase of neutral endopeptidase-24.11 with cellular density and enzyme modulation with an inhibitor on human Reh6 cell line

Neutral endopeptidase (EC 3.4.24.11, NEP) is an ectoenzyme, identified as the common acute lymphoblastic leukemia antigen (CALLA, CD10). This enzyme is involved in the inactivation of regulatory peptides such as enkephalins and atrial natriuretic peptide and its expression on the cell surface is therefore essential. NEP levels have been measured under different conditions on leukemic cell lines. NEP activity per cell was found to increase during the cell growth of Reh6 and CEM cells, a cell-cell contact mechanism being suggested by experiments using Transwell cell chambers. The same process was not observed with ICIG-7 fibroblasts. The numbers of enzymatic sites was also found to be selectively modulated by treatment with 0.1 microM N-[3-(R,S)-[(hydroxyamino)carbonyl]-2-benzyl-1-oxopropyl]glycine (HACBOGly), a potent (Ki = 1.4 nM) and specific inhibitor of NEP. A maximal 13% decrease in sites was observed after 8 hr incubation, this effect disappearing after 12 hr. This weak but specific negative modulation was not observed with a compound, chemically related to HACBOGly, which has a 10,000-fold lower inhibitory potency. The modulation was inhibited by low temperature or monensin treatment and could be brought about by an internalization of the enzyme, compensated for by an increased biosynthesis or by the sequestration of NEP in a non-membranous compartment.

Early modifications of outgrowth and metallo-endopeptidase activity in fibroblasts from rat cutaneous explants after local gamma-irradiation: dermis cellularity and collagen fibre alterations

The initial response to local gamma-irradiation of skin was investigated in fibroblasts from cutaneous explants after doses of 4, 8, 12, 16 or 20 Gy. On the day of irradiation, fibroblast outgrowth was inhibited in a dose-dependent manner, but by day 7 post-irradiation, cell restoration occurred especially in explants exposed to 4 or 8 Gy. The dose-dependent inhibition of fibroblast outgrowth correlated with the decrease in cellular metallo-endopeptidase (MEP) activity against succinyl trialanine paranitroanilide. However, the secretion of this MEP activity was 10-fold higher in the culture medium after the lowest irradiation dose (4 Gy). Its inhibition profile was not modified after local irradiation, whatever the dose. In vivo, the cell density of mastocytes, pericytes and endothelial cells decreased after irradiation. Moreover, damaged collagen was observed in the superficial dermis after local irradiation. These results strongly suggest that this MEP may be involved in the alterations occurring in dermal connective tissue components after skin irradiation. The rapid decrease with the dose in fibroblast outgrowth and MEP activity also suggests that these two parameters may provide useful tools for dosimetric assay of the heterogeneity and extent of irradiated areas.