LEKTI, a Novel 15-Domain Type of Human Serine Proteinase Inhibitor

Abstract

Proteinase inhibitors are important negative regulators of proteinase action in vivo. We have succeeded in isolating two previously unknown polypeptides (HF6478 and HF7665) from human blood filtrate that are parts of a larger precursor protein containing two typical Kazaltype serine proteinase inhibitor motifs. The entire precursor protein, as deduced from the nucleotide sequence of the cloned cDNA, exhibits 15 potential inhibitory domains, including the Kazal-type domains, HF6478, HF7665, and 11 additional similar domains. An inhibitory effect of HF7665 on trypsin activity is demonstrated. Because all of the 13 HF6478-and HF7665-related domains share partial homology to the typical Kazal-type domain but lack one of the three conserved disulfide bonds, they may represent a novel type of serine proteinase inhibitor. The gene encoding the multidomain proteinase inhibitor, which we have termed LEKTI, was localized on human chromosome 5q31-32. As shown by reverse transcriptase-polymerase chain reaction and Northern blot analysis, it is expressed in the thymus, vaginal epithelium, Bartholin's glands, oral mucosa, tonsils, and the parathyroid glands. From these results, we assume that LEKTI may play a role in antiinflammatory and/or antimicrobial protection of mucous epithelia.Proteinases are enzymes required for nonspecific processes of digestion and intracellular protein turnover as well as specific proteolytic activation of inactive precursors of many regulatory proteins, such as enzymes and peptide hormones. In addition, they are involved in several processes of extracellular matrix remodeling. Depending on the nature of their reactive center, they are subdivided into the classes of serine, cysteine, aspartate, and metalloproteinases (for review see Ref. 1). To control the action of proteinases in vivo, organisms produce another group of proteins, namely the proteinase inhibitors (for review see Refs. 2-4). Indeed, many pathological effects are due to the non-regulated action of endogenously produced proteinases or such proteinases encoded or synthesized by viruses, bacteria, and parasites (for review see Ref. 5). For instance, a genetically determined fault of the ␣ 1 -proteinase inhibitor may lead to an enhanced proneness to lung emphysema caused by uncontrolled action of leukocyte elastase (6 -8). Thus, proteinase inhibitors represent an important therapeutic tool for a large number of different disorders.Here we report the isolation of two peptides (HF6478 and HF7665) from human blood filtrate (hemofiltrate), which may represent a novel class of proteinase inhibitor. Blood filtrate, a by-product of ultrafiltration of the blood from patients with acute renal failure, is routinely used by us as a source for the systematic as well as random isolation of novel human peptides (9). Due to the cut-off limit of the hemofilters (approximately 20,000 Da), it mainly contains peptides exhibiting a molecular mass below 20,000 Da. Nevertheless, we succeeded in isolating members of many different peptide/protein families suc...

The Solution Structure of a Chimeric LEKTI Domain Reveals a Chameleon Sequence

“…As single domains 1, 5, and 6 have been isolated from ultrafiltrates of human blood (10,17) and a 30 kDa LEKTI fragment corresponding to approximately four domains starting with domain 8 was isolated from human epidermal keratinocyte-conditioned media (18), we suggest that both single-and multiple-domain fragments of LEKTI occur naturally.…”

“…Testing of various serine proteinases showed that domain 6 is an efficient (IC 50 = 150 nM) but temporary inhibitor of trypsin (10). Trypsin inhibitory activity has also been found for natural domain 5 and recombinant domains 8 and 15 (17).…”

Association between polymorphisms in the SPINK5 gene and atopic dermatitis in the Japanese

“…SPINK5 is involved in regulation of proteolysis in epithelia formation and keratinocyte terminal differentiation, and some mutations in the SPINK5 gene cause defects in the skin barrier. 8 SPINK5 is expressed in thymus, tonsil and oral mucosa, 10 and it is suggested that abnormal maturation of T lymphocytes in patients with Netherton syndrome alters Th2-type responsiveness to allergens, leading to elevated IgE levels. 8 A recent study of Caucasian AD families showed that maternally derived alleles of the SPINK5 gene are associated with development of atopic diseases such as AD and asthma, suggesting a parent-oforigin effect in the development of atopic diseases.…”

Prenatal diagnosis of Comel-Netherton syndrome with PGD, case report and review article

“…SPINK5 (serin protease inhibitor Kazal-type 5) encodes the Kazal-type serin protease inhibitor domains. LECT1 is thought to be involved in the regulation of proteolysis in skin barrier formation and immunity and this protein is highly expressed in thymus and mucous epithelia [22].…”

“…Low dose oral corticosteroids, etretinate and psoralen ultraviolet A therapy was also used. Topical tacrolimus will likely achieve minimal benefit, and may be contraindicated for patients with extensive skin involvement with concern for systemic absorption [22,31].…”