Epidermal Structure and Function

Abstract

Cutaneous T-cell lymphomas (CTCL) are the most common primary skin lymphomas and characterized by accumulation of malignant T-cells in the skin. The early lesion resembles both clinical and histological benign inflammatory disorders with hyperproliferative epidermis with infiltration of T-cells. Despite considerable progress in the understanding of molecular mechanisms involved in the malignant transformation of T-cells, it is largely unknown what causes the morphological and histopathological features of the disease. Here we take advantage of a novel, organotypic 3D-model of CTCL to show that malignant T-cells profoundly changes the behavior and growth of keratinocytes. Thus, organotypic 3D-cultures with human keratinocytes, fibroblasts and malignant T-cells display a disorganized stratification and hypercromatic cells resembling the early hyperproliferative stage of CTCL. Furthermore, hyperproliferation was followed by a down regulation of differentiation markers such as keratin 10 and involucrin. Interestingly, we observed a loss of attachment between the epithelial-and mesenchymal compartment, and immunohistochemistry revealed a greatly reduced expression of E-cadherin compared to controls. In conclusion, we provide the first evidence that malignant T-cells orchestra the histopathological skin changes seen in CTCL. The human Dermokine gene (DMKN) is located at 19q13.1 within the « Stratified epithelium Secreted peptides Complex » (SSC) locus, surrounded by 2 other genes encoding proteins secreted in the stratified epithelia, namely Suprabasin (SBSN) and Keratinocyte-differentiation-associated protein (KRTDAP). DMKN expression leads to production of 4 isoform families, each of them displaying a different histological and subcellular location. We recently showed that the ubiquitous and intracellular DMKN δ isoforms are involved in endovesicular trafficking via activation of the small GTPase Rab5. Contrary to δ isoforms, DMKN β and γ are specifically expressed and secreted by the granular keratinocytes. Thus they could play a specific role in the late steps of epidermal differentiation. We studied the Dmkn gene expression in the mouse. SSC locus is located in the syntenic region of murine chromosome 7. RT-PCR and RACE-PCR experiments as well as in silico analysis of the murine genomic sequence show mRNA expression for the α, β and γ families but not for the δ one. Splicing of the Dmkn mRNA is thus less complex than its human counterpart. Quantitative RT-PCR analysis revealed that Dmkn, Sbsn and Krtdap expression is upregulated in the skin of adult and old mice compared to that of newborns. During skin wound healing, Dmkn β and γ are highly expressed in the late stages of re-epithelialization, like many other epidermal differentiation markers. Finally, we developed Dmkn βγ knockout mice. The animals are viable and show no visible differences compared to wild type mice. However, quantitative RT-PCR and immunoblot experiments revealed a deregulated expression of late epidermis differentiation genes. In particular, ...