T-cadherin is a unique member of the cadherin superfamily that lacks the transmembrane and cytoplasmic domains, and is instead linked to the cell membrane via a glycosyl-phosphatidylinositol anchor. We previously reported that T-cadherin was specifically expressed on the basal keratinocytes of the epidermis, and the expression of T-cadherin was significantly reduced in invasive cutaneous squamous cell carcinoma (SCC) and in the lesional skin of psoriasis vulgaris. In this study, to obtain an insight into the role of T-cadherin in keratinocytes, we used transfection methods and examined the effect of overexpression or knockdown of T-cadherin in immortalized keratinocyte cell lines derived from SCC. T-cadherin overexpressed cells showed clearly reduced cell proliferation, but the influence of cell-cell adhesiveness and cell mobility was not detected. Using a tetracycline-regulated expression system, we also confirmed that the suppression of cell proliferation was dependent on the expression level of T-cadherin. Cell cycle analysis demonstrated that over expression of T-cadherin induced a delay in the G(2)/M phase. Our findings suggest that T-cadherin acts as an endogenous negative regulator of keratinocyte proliferation and its inactivation is the cause for keratinocyte hyperproliferation in SCC or in psoriasis vulgaris.

SummaryRecently air pollutants and irritants have been labelled as possible exogenous risk factors for allergic disorders. Although the underlying causes of allergic disorders such as atopic dermatitis and asthma remain unclear, the T helper type 2 (Th2) cell-mediated allergic inflammatory cascade may contribute to their pathogenesis. In the last decade, it has been documented that one of the candidates for triggering Th2 commitment is thymic stromal lymphopoietin (TSLP), the expression of which is up-regulated in the lesions of allergic patients. Here, we describe TSLP function in a fluorescein isothiocyanate (FITC) -induced contact hypersensitivity (CHS) model. A cytokine profile indicated that the model was dominantly mediated by the Th2 milieu. Interestingly, TSLP was increased in the skin during the sensitization phase when stimulated by a solvent, dibutyl phthalate (DBP), but not by FITC hapten or another solvent, acetone. Ear swelling in FITC-induced CHS was totally abrogated by removing DBP from the sensitization or elicitation phase, and was restored by complementary injection of TSLP. Inversely, the ear swelling was suppressed by injection of small interfering RNA against TSLP during the sensitization phase, which was concomitant with decreasing expression of interleukin-4 at the swollen skin site. Taken together, DBP-induced TSLP during the sensitization phase plays a role in establishing FITC-induced CHS and may be one of the causes of Th2 commitment in the model, suggesting that certain environmental toxins, such as DBP, may endow pro-allergic and atopic predisposition in humans or animals.

T-cadherin is a glycosyl-phosphatidylinositol (GPI) anchored cadherin molecule. We previously reported that T-cadherin is normally expressed on the basal keratinocytes of the epidermis and is down-regulated in cutaneous squamous cell carcinoma (SCC). We found that expression of T-cadherin in cutaneous squamous carcinoma cells regulated level of surface β β β β 1 integrin, which functioned as extracellular matrix (ECM) receptor. Involvement of T-cadherin in β β β β 1 integrin trafficking was studied using three different stable cell lines with cytomegalovirus (CMV)-driven over-expression, tetracycline (Tet)-inducible expression and RNAi-mediated suppressed expression of T-cadherin. Pulse-chase analysis using a cholesterol-depleting reagent and a tyrosine kinase inhibitor showed that β β β β 1 integrin mainly internalized via caveolae. Over-expression of T-cadherin suppressed the internalization of both β β β β 1 integrin and cholera toxin (CTX), a marker of caveolaemediated endocytosis. By Western blot analysis of tyrosine-kinase target molecules, we demonstrated a reduced level of EGF receptor (EGFR)-phosphorylation in T-cadherin over-expressing cells. In addition, studies using EGF and EGFR specific inhibitors revealed that EGFR activation stimulated β β β β 1 integrin internalization. Taking these results together, T-cadherin may modulate cell-matrix adhesion in basal keratinocytes as well as invasive potency in SCC by regulating surface level of β β β β 1 integrin.