LEKTI proteolytic processing in human primary keratinocytes, tissue distribution and defective expression in Netherton syndrome

SPINK5, encoding the putative multi-domain serine protease inhibitor LEKTI, was recently identified as the defective gene in the severe autosomal recessive ichthyosiform skin condition, Netherton syndrome (NS). Using monoclonal and polyclonal antibodies, we show that LEKTI is a marker of epithelial differentiation, strongly expressed in the granular and uppermost spinous layers of the epidermis, and in differentiated layers of stratified epithelia. LEKTI expression was also demonstrated in normal differentiated human primary keratinocytes (HK) through detection of a 145 kDa full-length protein and a shorter isoform of 125 kDa. Both proteins are N-glycosylated and rapidly processed in a post-endoplasmic reticulum compartment into at least three C-terminal fragments of 42, 65 and 68 kDa, also identified in conditioned media. Processing of the 145 and 125 kDa precursors was prevented in HK by treatment with a furin inhibitor. In addition, in vitro cleavage of the recombinant 145 kDa precursor by furin generated C-terminal fragments of 65 and 68 kDa, further supporting the involvement of furin in LEKTI processing. In contrast, LEKTI precursors and proteolytic fragments were not detected in differentiated HK from NS patients. Defective expression of LEKTI in skin sections was a constant feature in NS patients, whilst an extended reactivity pattern was observed in samples from other keratinizing disorders, demonstrating that loss of LEKTI expression in the epidermis is a diagnostic feature of NS. The identification of novel processed forms of LEKTI provides the basis for future functional and structural studies of fragments with physiological relevanc

Expression of the beta 4 integrin subunit induces monocytic differentiation of 32D/v-Abl cells

The alpha 6 beta 4 integrin is the receptor for various laminin isoforms and is a component of the hemidesmosome. Increased expression levels of this integrin correlate with the aggressive phenotype of many epithelial tumors compared with surrounding normal tissue. Furthermore, the long cytoplasmic tail of the beta 4 integrin subunit has been implicated in several signal transduction pathways that are involved not only in invasion, but also in proliferation and apoptosis. Here we report that the exogenous expression of beta 4 integrin in 32D/v-abl-transformed cells reduces tumor aggressiveness in vivo and strongly inhibits cell proliferation in vitro by inducing monocytic differentiation. These effects are accompanied by growth arrest and p73 protein accumulation. The hypothesis that the inhibition of v-Abl oncogenic capacity could allow the activation of the endogenous c-Abl was tested in RKO cells. The results clearly demonstrated a strong increase of c-Abl phosphorylation that is accompanied by its association with p73 protein. Overall, the reported findings indicate that alpha 6 beta 4 integrin promotes growth arrest and differentiation by modulating Abl kinases and p73 protein pathway(s)

LEKTI proteolytic processing in human primary keratinocytes, tissue distribution and defective expression in Netherton syndrome

SPINK5, encoding the putative multi-domain serine protease inhibitor LEKTI, was recently identified as the defective gene in the severe autosomal recessive ichthyosiform skin condition, Netherton syndrome (NS). Using monoclonal and polyclonal antibodies, we show that LEKTI is a marker of epithelial differentiation, strongly expressed in the granular and uppermost spinous layers of the epidermis, and in differentiated layers of stratified epithelia. LEKTI expression was also demonstrated in normal differentiated human primary keratinocytes (HK) through detection of a 145 kDa full-length protein and a shorter isoform of 125 kDa. Both proteins are N-glycosylated and rapidly processed in a post-endoplasmic reticulum compartment into at least three C-terminal fragments of 42, 65 and 68 kDa, also identified in conditioned media. Processing of the 145 and 125 kDa precursors was prevented in HK by treatment with a furin inhibitor. In addition, in vitro cleavage of the recombinant 145 kDa precursor by furin generated C-terminal fragments of 65 and 68 kDa, further supporting the involvement of furin in LEKTI processing. In contrast, LEKTI precursors and proteolytic fragments were not detected in differentiated HK from NS patients. Defective expression of LEKTI in skin sections was a constant feature in NS patients, whilst an extended reactivity pattern was observed in samples from other keratinizing disorders, demonstrating that loss of LEKTI expression in the epidermis is a diagnostic feature of NS. The identification of novel processed forms of LEKTI provides the basis for future functional and structural studies of fragments with physiological relevance