1. ¹Laboratory of Molecular and Cell Biology, Istituto Dermopatico dell'Immacolata, IDI-IRCCS, Rome, Italy
2. ²INSERM U563, Paul Sabatier University, Toulouse, France
3. ³Department of Medical Genetics, Purpan Hospital, Toulouse, France

Correspondence: Dr Marina D'Alessio, Laboratory of Molecular and Cell Biology, Istituto Dermopatico dell'Immacolata, IDI-IRCCS, Via dei Monti di Creta 104, Rome 00167, Italy. E-mail: dalessio@idi.it

⁴These authors contributed equally to this work.

Received 2 August 2005; Revised 9 September 2005; Accepted 12 September 2005; Published online 22 December 2005.

Abstract

The multidomain serine protease inhibitor lymphoepithelial Kazal-type related inhibitor (LEKTI) represents a key regulator of the proteolytic events occurring during epidermal barrier formation and hair development, as attested by the severe autosomal recessive ichthyosiform skin condition Netherton syndrome (NS) caused by mutations in its encoding gene, serine protease inhibitor Kazal-type 5 (SPINK5). Synthesized as a proprotein, LEKTI is rapidly cleaved intracellularly, thus generating a number of potentially bioactive fragments that are secreted. Here, we show that SPINK5 generates three classes of transcripts encoding three different LEKTI isoforms, which differ in their C-terminal portion. In addition to the previously described 15 domain isoform, SPINK5 encodes a shorter LEKTI isoform composed of only the first 13 domains, as well as a longer isoform carrying a 30-amino-acid residue insertion between the 13th and 14th inhibitory domains. We demonstrate that variable amounts of SPINK5 alternative transcripts are detected in all SPINK5 transcriptionally active tissues. Finally, we show that in differentiated cultured human keratinocytes all SPINK5 alternative transcripts are translated into protein and that the LEKTI precursors generate distinct secreted C-terminal proteolytic fragments from a similar cleavage site. Since several data indicate a biological role for the pro-LEKTI-cleaved polypeptides, we hypothesize that the alternative processing of the SPINK5 pre-messenger RNA represents an additional mechanism to further increase the structural and functional diversity of the LEKTI bioactive fragments.