Expression of tenascin-C splice variants by human skin cells.

Tenascin-C is an extracellular matrix glycoprotein that is expressed in a spatially and temporally restricted pattern. Various functionally different tenascin-C isoforms can be expressed as a result of alternative splicing of the pre-mRNA. Previously we identified human epidermal keratinocytes as a source of tenascin-C in healing wounds. In this study, we investigated whether different tenascin-C transcripts are expressed by epidermal keratinocytes and dermal fibroblasts. In addition, we compared expression of tenascin-C splice variants at the mRNA and protein levels in tissue samples of normal and diseased skin. Northern blot analysis revealed two major tenascin-C mRNA transcripts of approximately 7500 and 5800 nucleotides in cultured epidermal keratinocytes and fibroblasts, and in biopsies. Although both dermal fibroblasts and epidermal keratinocytes predominantly expressed the larger tenascin-C mRNA, epidermal keratinocytes expressed smaller transcripts at higher levels than dermal fibroblasts. In keratinocytes the levels of the two mRNAs were differentially affected by inflammatory cytokines that increased tenascin-C expression in these cells. The addition of IFN gamma slightly increased the proportion of large transcripts. In contrast, TNF alpha favoured expression of smaller tenascin-C transcripts, and IL-4 equally affected the expression of large and small tenascin-C mRNAs. To enable detection of tenascin-C transcripts that are expressed at very low levels, we amplified by polymerase chain reaction the fibronectin type III repeats whose expression is regulated by alternative splicing. In cDNA of cultured keratinocytes and fibroblasts, and in skin biopsies, several tenascin-C transcripts could be detected that corresponded to tenascin-C variants including different numbers of fibronectin type III repeats. Distribution of tenascin-C isoforms at the protein level was studied immunohistochemically in healthy skin, wounds, psoriatic lesions and epidermal tumours and hyperplasia. No differences were observed in reactivity between an antibody that binds all tenascin-C isoforms and antibodies that bind fibronectin type III repeats that can be spliced out from smaller tenascin-C isoforms. We conclude that the tenascin-C isoforms that are translated from transcripts that we identified at the mRNA level seem to be distributed similarly in the conditions investigated.