Selenocysteine is incorporated cotranslationally at UGA codons, normally read as stop codons, in several bacterial proteins and in the mammalian proteins glutathione peroxidase (GPX), selenoprotein P and Type I iodothyronine 5' deiodinase (5'DI). Previous analyses in bacteria have suggested that a stem-loop structure involving the UGA codon and adjacent sequences is necessary and sufficient for selenocysteine incorporation into formate dehydrogenase and glycine reductase. We used the recently cloned 5'DI to investigate selenoprotein synthesis in eukaryotes. We show that successful incorporation of selenocysteine into this enzyme requires a specific 3' untranslated (3'ut) segment of about 200 nucleotides, which is found in both rat and human 5'DI messenger RNAs. These sequences are not required for expression of a cysteine-mutant deiodinase. Although there is little primary sequence similarity between the 3'ut regions of these mRNAs and those encoding GPX, the 3'ut sequences of rat GPX can substitute for the 5'DI sequences in directing selenocysteine insertion. Computer analyses predict similar stem-loop structures in the 3'ut regions of the 5'DI and GPX mRNAs. Limited mutations in these structures reduce or eliminate their capacity to permit 5'DI translation. These results identify a 'selenocysteine-insertion sequence' motif in the 3'ut region of these mRNAs that is essential for successful translation of 5'DI, presumably GPX, and possibly other eukaryotic selenocysteine-containing proteins.

T cells play a pathogenic role in many inflammatory and certain malignant skin diseases, including psoriasis, atopic and allergic contact dermatitis, and cutaneous T-cell lymphoma. Memory T cells that infiltrate the skin express a unique skin-homing receptor called cutaneous lymphocyte-associated antigen (CLA), a carbohydrate epitope that facilitates the targeting of T cells to inflamed skin. CLA is defined by both its reactivity with a unique monoclonal antibody, HECA-452, and its activity as a ligand for E-selectin, but the structure of the protein component of CLA has not previously been defined. Here we report that CLA is an inducible carbohydrate modification of P-selectin glycoprotein ligand-1 (PSGL-1), a known surface glycoprotein that is expressed constitutively on all human peripheral-blood T cells. Cultured peripheral-blood T cells can be differentiated into CLA-bearing cells, which bind both E-selectin and P-selectin, or CLA-negative cells, which bind P-selectin but do not bind E-selectin, suggesting that there is independent regulation of selectin-binding phenotypes. We propose that differential post-translational modification of a single cell-surface receptor, PSGL-1, mediated by fucosyltransferase VII, serves as a mechanism for regulating tissue-specific homing of memory T cells.

Resting epidermal keratinocytes contain large amounts of interleukin 1 (IL-1), but the function of this cytokine in the skin remains unclear. To further define the role of IL-1 in cutaneous biology, we have generated two lines of transgenic mice (TgIL-1.1 and TgIL-1.2) which overexpress IL-la in basal keratinocytes. There was high-level tissuespecific expression of transgene mRNA and protein and large quantities of IL-lei were liberated into the circulation from epidermis in both lines. TgIL-1.1 mice, which had the highest level of transgene expression, developed a spontaneous skin disease characterized by hair loss, scaling, and focal inflammatory skin lesions. Histologically, nonlesional skin of these animals was characterized by hyperkeratosis and a dermal mononuclear cell infiltrate of macrophage/monocyte lineage.

The goal of this study was to determine the mechanisms by which dendritic cells (DCs) in blood could interact with endothelium, a prerequisite to extravasation into tissues. Our results indicate that DCs express both HECA-452–reactive and nonreactive isoforms of P-selectin glycoprotein ligand 1 (PSGL-1) and can tether and roll efficiently on E- and P-selectin under flow conditions in vitro. Freshly isolated blood DCs were further observed to roll continuously along noninflamed murine dermal endothelium in vivo. This interaction is strictly dependent on endothelial selectins, as shown by experiments with blocking antibodies and with E- and P-selectin–deficient mice. We hypothesize that DCs in blood are constitutively poised at the interface of blood and skin, ready to extravasate upon induction of inflammation, and we showed that cutaneous inflammation results in a rapid recruitment of DCs from the blood to tissues. We propose that this is an important and previously unappreciated element of immunosurveillance.