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J Cell Sci. 2005 May 1;118(Pt 9):1981-9. Epub 2005 Apr 19.

Increased keratinocyte proliferation by JUN-dependent expression of PTN and SDF-1 in fibroblasts.

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  • 1Division of Signal Transduction and Growth Control, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.

Abstract

In skin, fibroblasts of the connective tissue play a decisive role in epidermal homeostasis and repair by contributing to the regulation of keratinocyte proliferation and differentiation. The AP-1 transcription factor subunit JUN plays a crucial role in this mesenchymal-epithelial interplay by regulating the expression of two critical paracrine-acting cytokines, keratinocyte growth factor (KGF) and granulocyte-macrophage colony-stimulating factor (GM-CSF). We have performed gene expression profiling of wild-type and Jun(-/-) mouse embryonic fibroblasts to identify additional players involved in this complex network, and have found pleiotrophin (PTN) and the stromal cell-derived factor 1 (SDF-1) as novel JUN-regulated factors. Both cytokines are expressed by dermal fibroblasts in vivo, as shown by semi-quantitative RT-PCR and in situ hybridization on murine skin sections. Using a heterologous feeder layer co-culture system, we demonstrated that PTN and SDF-1 exert a mitogenic effect on primary human keratinocytes. Moreover, SDF-1-induced keratinocyte proliferation could be specifically inhibited by neutralizing antibodies against SDF-1 or its receptor, CXCR4. Consistent with its role in promoting keratinocyte growth, PTN was upregulated during cutaneous wound healing in vivo. Interestingly, co-cultivation with keratinocytes stimulated PTN expression but repressed SDF-1 production in fibroblasts, demonstrating the complexity of the paracrine regulatory cytokine networks that control skin homeostasis and regeneration.

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