Regulation of Expression of B7 by Murine Langerhans Cells: A Direct Relationship Between B7 mRNA Levels and the Level of Surface Expression of B7 by Langerhans Cells

Cultured BALB/c epidermal Langerhans cells express high levels of the costimulatory molecule B7 on their surfaces relative to levels expressed on fresh Langerhans cells. Quantitation of relative amounts of B7 mRNA in fresh epidermal cells and cultured epidermal cells following amplification of mRNA signals via reverse transcriptase – polymerase chain reaction, hybridization of PCR products with radiolabeled internal oligonucleotide probes, resolution of hybrids in non-denaturing polyacrylamide gels, and detection by autoradiography revealed dramatically (approximately one thousandfold) higher levels of B7 mRNA in cultured epidermal cells (10-40% 1-A+) as compared with fresh epidermal cells (1 – 4% I-A+). Levels of B7 mRNA in cultured epidermal cells were also substantially greater than those detected in a reference B lymphoma cell line (CH-1). Analysis of 87 mRNA expression in subpopulations of cultured epidermal cells demonstrated that essentially all of the B7 mRNA was present in Langerhans cells; cells bearing I-A and CD45 antigens. Cultured keratinocytes did not contain appreciable amounts of B7 mRNA. These results are consistent with previous data regarding surface expression of 87 by cLC and also demonstrate that fLC are essentially devoid of B7 mRNA and surface protein

Matriptase cleaves EpCAM and TROP2 in keratinocytes, destabilizing both proteins and associated claudins

The homologs EpCAM and TROP2, which both interact with claudin-1 and claudin-7, are frequently coexpressed in epithelia including skin. Intestine uniquely expresses high levels of EpCAM but not TROP2. We previously identified EpCAM as a substrate of the membrane-anchored protease matriptase and linked HAI-2, matriptase, EpCAM and claudin-7 in a pathway that is pivotal for intestinal epithelial cells (IEC) homeostasis. Herein, we reveal that TROP2 is also a matriptase substrate. Matriptase cleaved TROP2 when purified recombinant proteins were mixed in vitro. TROP2, like EpCAM, was also cleaved after co-transfection of matriptase in 293T cells. Neither EpCAM nor TROP2 cleavage was promoted by protease-disabled matriptase or matriptase that harbored the ichthyosis-associated G827R mutation. We confirmed that EpCAM and TROP2 are both expressed in skin and detected cleavage of these proteins in human keratinocytes (HaCaT cells) after the physiologic inhibition of matriptase by HAI proteins was relieved by siRNA knockdown. Knockdown of EpCAM or TROP2 individually had only small effects on claudin-1 and claudin-7 levels, whereas elimination of both markedly diminished claudin levels. HAI-1 knockdown promoted EpCAM and TROP2 cleavage accompanied by reductions in claudins, whereas HAI-2 knockdown had little impact. Double knockdown of HAI-1 and HAI-2 induced nearly complete cleavage of EpCAM and TROP2 and drastic reductions of claudins. These effects were eliminated by concurrent matriptase knockdown. Decreases in claudin levels were also diminished by the lysosomal inhibitor chloroquine and cleaved EpCAM/TROP2 fragments accumulated preferentially. We demonstrate that TROP2 and EpCAM exhibit redundancies with regard to regulation of claudin metabolism and that an HAI, matriptase, EpCAM and claudin pathway analogous to what we described in IECs exists in keratinocytes. This study may offer insights into the mechanistic basis for matriptase dysregulation-induced ichthyosis

Involvement of E-Cadherin in Thymus Organogenesisand Thymocyte Maturation

AbstractWe examined the role of E-cadherin expressed by thymic epithelial cells and immature thymocytes in thymus organogenesis and thymocyte development. ECCD-1 MAb, which blocks homotypic E-cadherin interactions, inhibited epithelial organization and thymocyte development in reaggregate fetal thymic organ cultures. It also interfered with the differentiation of fetal liver cells or fetal thymocytes within deoxyguanosine-treated thymic lobes, but did not affect thymocyte development in intact cultured fetal thymic lobes. In contrast, antibodies that selectively inhibit interactions between E-cadherin and αEβ7 integrins did not perturb thymic epithelial organization or thymocyte development, suggesting that homotypic E-cadherin interactions play an important role in thymus development and function

EpCAM (CD326) regulates intestinal epithelial integrity and stem cells via Rho-associated kinase

Humans with biallelic inactivating mutations in Epithelial Cell Adhesion Molecule (EpCAM) develop congenital tufting enteropathy (CTE). To gain mechanistic insights regarding EpCAM function in this disorder, we prepared intestinal epithelial cell (IEC) organoids and spheroids. IEC organoids and spheroids were generated fro

Antigen-Presenting Cells in Essential Fatty Acid—Deficient Murine Epidermis: Keratinocytes Bearing Class II (Ia) Antigens May Potentiate the Accessory Cell Function of Langerhans Cells

Essential fatty acid deficiency (EFAD) is a useful model for studying the role of (n-6) fatty acid metabolism in normal physiology. Because cutaneous manifestations are among the earliest signs of EFAD and because abnormalities in the distribution and function of tissue macrophages have been documented in EFAD rodents, we studied the distribution and function of Class II MHC (Ia) antigen-bearing cells in EFAD CS7B1/6 mouse epidermis. Immunofluorescence studies revealed 1.9–9.6 (mean ± SEM = 5.2 ± 2.6) times more class II MHC (Ia) antigen-bearing epidermal cells in suspensions prepared from EFAD as compared to normal skin. Analysis of epidermal sheets demonstrated similar numbers of dendritic Ia+ and NLDC145+ cells in EFAD and normal epidermis, however. This discrepancy occurred because some keratinocytes in EFAD epidermal sheets expressed class II MHC (Ia) antigens, whereas keratinocytes in normal mouse epidermis did not. Two-color flow cytometry confirmed that all Ia+ cells in normal epidermis are Langerhans (Ia+ NLDC145+) cells, whereas Ia+ cells in EFAD epidermis are comprised of Langerhans cells and a subpopulation of keratinocytes (Ia+ NLDC145-. Similar levels of Ia antigens were expressed on EFAD and normal Langerhans cells. EFAD and normal epidermal cells were also compared in several in vitro assays of accessory cell function. Epidermal cells prepared from EFAD C57B1/6 mice present the protein antigen DNP-Ova to primed helper T cells more effectively than epidermal cells prepared from normal animals. EFAD epidermal cells are also more potent stimulators of T cells in primary and secondary allogeneic mixed lymphocyte-epidermal cell reactions than normal epidermal cells. The functional differences between EFAD and normal epidermal cells do not appear to result from increased cytokine release or decreased prostaglandin production by EFAD epidermal cells. In view of these findings and the observation that the antigen-presenting cell activity of EFAD epidermal cells correlates with the number of Ia+ keratinocytes in epidermal cell preparations, Ia+ keratinocytes (in the presenceof Langerhans cells) may potentiate cutaneous immune responses in vitro and perhaps in vivo as well. these results also suggest that (n-6) fatty acids or metabolites of (n-6) fatty acids are involved in regulating the expression of class II MHC (Ia) antigens by keratinocytes in vivo

TGFβ1 Overexpression by Keratinocytes Alters Skin Dendritic Cell Homeostasis and Enhances Contact Hypersensitivity

Overexpression of transforming growth factor beta-1 (TGFβ1) in mouse epidermis causes cutaneous inflammation and keratinocyte hyperproliferation. Here we examined acute effects of TGFβ1 overproduction by keratinocytes on skin dendritic cells (DCs). TGFβ1 induction for 2 and 4 days increased the numbers and CD86 expression of B220+ plasmacytoid DCs (pDCs) and CD207+CD103+, CD207−CD103−CD11b+, and CD207−CD103−CD11b− dermal DCs (dDCs) in skin-draining lymph nodes (SDLNs). The dermis of TGFβ1-overexpressing mice had significantly more pDCs, CD207+CD103+ dDCs, and CD207−CD11b+ dDCs in the absence of increased dermal proliferation. Application of dye, tetramethyl rhodamine iso-thiocyanate (TRITC), in dibutylpthalate (DBP) solution after TGFβ1 induction increased the numbers of TRITC+CD207− dDCs in SDLNs, and augmented TRITC/DBP-induced Langerhans cell (LC) migration 72hours post TRITC treatment. Consistent with this, LC migration was increased in vitro by TGFβ1 overexpression in skin explants and by exogenous TGFβ1 in culture media. Transient TGFβ1 induction during DNFB sensitization increased contact hypersensitivity responses by 1.5-fold. Thus, elevated epidermal TGFβ1 alone is sufficient to alter homeostasis of multiple cutaneous DC subsets, and enhance DC migration and immune responses to contact sensitizers. These results highlight a role for keratinocyte-derived TGFβ1 in DC trafficking and in the initiation of skin inflammation

MFG-E8 Regulates Angiogenesis in Cutaneous Wound Healing

Our research group recently demonstrated that pericytes are major sources of the secreted glycoprotein and integrin ligand lactadherin (MFG-E8) in B16 melanoma tumors, and that MFG-E8 promotes angiogenesis via enhanced PDGF–PDGFRβ signaling mediated by integrin–growth factor receptor crosstalk. However, sources of MFG-E8 and its possible roles in skin physiology are not well characterized. The objective of this study was to characterize the involvement of MFG-E8 in skin wound healing. In the dermis of normal murine and human skin, accumulations of MFG-E8 were found around CD31+ blood vessels, and MFG-E8 colocalized with PDGFRβ+, αSMA+, and NG2+ pericytes. MFG-E8 protein and mRNA levels were elevated in the dermis during full-thickness wound healing in mice. MFG-E8 was diffusely present in granulation tissue and was localized around blood vessels. Wound healing was delayed in MFG-E8 knockout mice, compared with the wild type, and myofibroblast and vessel numbers in wound areas were significantly reduced in knockout mice. Inhibition of MFG-E8 production with siRNA attenuated the formation of capillary-like structures in vitro. Expression of MFG-E8 in fibrous human granulation tissue with scant blood vessels was less than that in granulation tissue with many blood vessels. These findings suggest that MFG-E8 promotes cutaneous wound healing by enhancing angiogenesis