Characterization and gene sequence of the precursor of elafin, an elastase-specific inhibitor in bronchial secretions

Constitutive and inducible expression of SKALP/elafin provides anti-elastase defense in human epithelia

Skin-derived antileukoproteinase (SKALP), also known as elafin, is a serine proteinase inhibitor first discovered in keratinocytes from hyperproliferative human epidermis. In addition to the proteinase inhibiting domain which is directed against polymorphonuclear leukocyte (PMN) derived enzymes such as elastase and proteinase 3, SKALP contains multiple transglutaminase (TGase) substrate domains which enable crosslinking to extracellular and cell envelope proteins. Here we show that SKALP is constitutively expressed in several epithelia that are continuously subjected to inflammatory stimuli, such as the oral cavity and the vagina where it co-localizes with type 1 TGase. All epithelia from sterile body cavities are negative for SKALP. In general, stratified squamous epithelia are positive, whereas pseudostratified epithelia, simple/glandular epithelia and normal epidermis are negative. SKALP was found in fetal tissues of the oral cavity from 17 wk gestation onwards where it continued to be expressed up to adult life. Remarkably, in fetal epidermis SKALP was found from week 28 onwards, but was downregulated to undetectable levels in neonatal skin within three months, suggesting a role during pregnancy in feto-maternal interactions or in the early maturation phase of the epidermis. Immunoelectron microscopy revealed the presence of SKALP in secretory vesicles including the lamellar granules. In culture models for epidermal keratinocytes we found that expression of the endogenous SKALP gene provided protection against cell detachment caused by purified elastase or activated PMNs. Addition of exogenous recombinant SKALP fully protected the keratinocytes against PMN-dependent detachment whereas superoxide dismutase and catalase were only marginally effective. These findings strongly suggest that the constitutive expression of SKALP in squamous epithelia, and the inducible expression in epidermis participate in the control of epithelial integrity, by inhibiting PMN derived proteinases.

Exons lost and found. Unusual evolution of a seminal vesicle transglutaminase substrate

The GP1G gene codes for three of the four abundant androgen-regulated secretory proteins produced by the guinea pig seminal vesicle. Sequencing of the entire 6.3-kilobase gene and comparison with other mammalian seminal vesicle secretory protein genes reveals a common three-exon, two-intron organization. However, significant sequence similarity between this group of genes is largely limited to their 5'-flanking regions and first exons, which code almost exclusively for signal peptides in each case. The first intron of GP1G does contain a region with high similarity to the coding exon of a human seminal vesicle secretory protein gene, semenogelin II. The 3' half of the GP1G gene appears to share a common ancestry with the human SKALP/elafin gene. Sequences related to the elafin promoter, coding, untranslated regions, and introns are clearly identifiable within the GP1G sequence. The elafin gene codes for a serine protease inhibitor and is expressed in a variety of different human tissues. To determine if the GP1G gene was also active outside of the seminal vesicle, RNA from a variety of guinea pig tissues was hybridized to a GP1G cDNA probe. At least three novel RNA bands hybridizing to the GP1G probe were detected in testis RNA samples, and GP1G-related mRNAs were also found in other tissues. These data suggest that these seminal vesicle secretory proteins may have functional roles outside the reproductive system.

Elafin, a serine elastase inhibitor, attenuates post-cardiac transplant coronary arteriopathy and reduces myocardial necrosis in rabbits afer heterotopic cardiac transplantation

We have related experimentally induced post-cardiac transplant coronary arteriopathy to increased elastolytic activity, IL-1beta, fibronectin-mediated inflammatory and smooth muscle cell (SMC) migration, and SMC proliferation. Since our in vitro studies show that a serine elastase releases SMC mitogens and facilitates IL-lbeta induction of fibronectin, we hypothesized that administration in vivo of the specific serine elastase inhibitor, elafin, would decrease the post-cardiac transplant coronary arteriopathy. Cholesterol-fed rabbits underwent a heterotopic cardiac transplant without immunosuppression and received elafin (1.79 mg/kg per d continuous infusion after a 9 mg bolus, n = 6) or vehicle (n = 6). 1 wk later, hearts were harvested for morphometric, immunohistochemical, and biochemical analyses. A > 70% decrease in the total number of coronary arteries with intimal thickening in elafin-treated compared to control donor hearts (P < 0.002) was associated with reduced vascular elastolytic activity judged by fewer breaks in the internal elastic lamina (P < 0.03), less accumulation of immunoreactive fibronectin (P < 0.02), and reduced cell proliferation quantified by proliferating cell nuclear antigen (P < 0.0001). Despite myocardial lymphocytic infiltration, wet weight of elafin-treated donor hearts was reduced by 50% compared to untreated controls (P < 0.002) and associated with relative preservation of myocyte integrity, instead of extensive myocardial necrosis (P < 0.004). This protective effect correlated with decreased myocardial elastolytic activity (P < 0.0001) and inflammatory cell proliferation (P < 0.0001) and with an elafin-inhibitable elastase in lymphocytes. Serine elastase activity thus appears an important therapeutic target for post-cardiac transplant coronary arteriopathy and myocardial necrosis induced by rejection.

Antiprotease activity in urine of patients with inflammatory skin disorders

Polymorphonuclear leukocytes contain well-defined proteolytic enzymes in their azurophilic granules that can be released into tissues during inflammation, producing a localized excess of proteases that causes a protease-antiprotease imbalance with subsequent tissue destruction. The antiproteolytic compounds of the epidermis, such as the protease inhibitors elafin and antileukoprotease, are thought to counteract the proteolytic tissue damage. We investigated the urine of patients suffering from inflammatory skin conditions (e.g., erysipelas, psoriasis) for the presence of urinary antiprotease activities. Purification of elastase-inhibitory activities from pooled urine samples by cation exchange high-performance liquid chromatography and preparative and analytical reverse-phase high-performance liquid chromatography yielded two different types of inhibitors. One was a cationic, acid-stable, and elastase-specific inhibitor of M(r) 6,000 by size-exclusion high-performance liquid chromatography. N-terminal amino acid sequence analysis of the first 28 residues showed identity with elafin, an elastase-specific inhibitor recently isolated from psoriatic scales. The second anti-protease activity was due to two forms of urinary bikunin, the inhibitory subunit of inter-alpha-inhibitor. Both bikunin fragments, with M(r) 4,000 and 16,000, were identified by N-terminal amino acid sequence analysis of the first 10 residues and were characterized by an antiproteolytic profile against human leukocyte elastase, cathepsin G, and trypsin. Urinary protease inhibitors may serve as diagnostic markers of inflammatory diseases.

Regulation of proteolytic activity in tissues

Degradation of tissue proteins is controlled by multiple means. These include regulation of the synthesis of proteinases, activation of the zymogen forms, the activity of the mature proteinase, and the degradation of these enzymes and the substrates. Mature proteinases can be controlled by pH, calcium ions, ATP, lipids and the formation of complexes with other proteinases, proteoglycans, and inhibitors.