Signal transduction in normal and neoplastic keratinocytes

AGE-modified collagens I and III induce keratinocyte terminal differentiation through AGE receptor CD36: epidermal-dermal interaction in acquired perforating dermatosis

To clarify the molecular mechanism underlying the transepidermal extrusion of dermal collagen in acquired perforating dermatosis (APD) associated with diabetes mellitus and renal failure, we studied the interaction between advanced glycation end product (AGE)-modified extracellular matrix proteins and keratinocytes (KCs) in a cell culture system. The expression of involucrin (INV) and keratin 10 was significantly enhanced in normal human KCs grown on AGE-modified collagen I or III compared with cells grown on unmodified collagen I or III. Glycated collagens I and III preferentially induced the expression of AGE receptor CD36, but not of other AGE receptors. KCs induced to terminal differentiation demonstrated markedly elevated CD36 expression. Glycated collagen I- and III-induced INV expression was partially blocked by the anti-CD36 antibody (Ab). These substrates also induced epidermal matrix metalloproteinase 9 (MMP-9) expression. Lesional skin from APD patients reacted moderately or strongly with the anti-CD36 Ab as well as the anti-MMP-9 Ab in the epidermal cells surrounding the collagenous materials being eliminated. These results suggest that exposing KCs to AGE-modified interstitial collagen (types I and III) by scratching induces terminal differentiation of KCs via the AGE receptor (CD36), leading to the upward movement of KCs together with glycated collagen.

Elastin peptides induce migration and terminal differentiation of cultured keratinocytes via 67 kDa elastin receptor in vitro: 67 kDa elastin receptor is expressed in the keratinocytes eliminating elastic materials in elastosis perforans serpiginosa

To delineate the molecular mechanism of transepidermal elimination of dermal elastic materials in elastosis perforans serpiginosa, the interaction between elastin and cultured keratinocytes was studied in vitro. Synthetic elastin peptide VGVAPG elicited chemotactic responses to the cultured keratinocytes at the dose of 10-9 M. Treatment of keratinocytes with 10-6 or 10-5 M elastin peptides resulted in the suppression of cell growth and the increased expression of involucrin and transglutaminase-1, markers of terminal differentiation. When cultured keratinocytes were treated with the elastin peptides, the expression of 67 kDa elastin receptor was increased. The induction of terminal differentiation by elastin peptides was attenuated by the treatment with the combination of anti-67 kDa elastin receptor antibody. The results indicate that elastin is a potent inducer of migration and terminal differentiation of cultured keratinocytes, which is mediated by the 67 kDa elastin receptor. In the lesional skins of patients with elastosis perforans serpiginosa, the 67 kDa elastin receptor was specifically expressed in the epidermis immediately surrounding the elastic materials that were being eliminated. The elastin receptor may be involved in the interaction between keratinocytes and elastin in elastosis perforans serpiginosa.

Distinct P-cadherin expression in cultured normal human keratinocytes and squamous cell carcinoma cell lines

Spatially regulated expression of E (epithelial)- and P (placental)-cadherins is crucial for maintaining normal epidermal architecture. In cutaneous squamous cell carcinomas (SCCs), aberrant P-cadherin expression is often observed in "squamoid" cancer cells, whereas E-cadherin expression in cancer cells is generally reduced. Therefore, it is plausible that SCC cells have acquired the ability to express P-cadherin and that P-cadherin plays a role in tumor progression. To address the issue, the in vitro effect of extracellular calcium on differentiation is a good model for investigating P-cadherin in normal and neoplastic skin. With elevations in extracellular calcium, human SCC cell line (DJM-1) cells initiate de novo synthesis of P-cadherin and express P-cadherin on the cell surface, whereas in normal human keratinocytes, P-cadherin expression on the cell surface is enhanced via the translocation from the cytosol to the cell membrane and/or the stabilization of P-cadherin at the cell surface. DJM-1 cells maintain P-cadherin expression on the cell surface at high levels for over 4 days after calcium elevation, whereas normal human keratinocytes cannot sustain cell surface P-cadherin when the cells are cultured in high calcium for more than 2 days. P-cadherin synthesis in DJM-1 cells is regulated at translational levels by extracellular calcium concentrations. SCC cells have the ability to produce P-cadherin by a mechanism not observed in normal keratinocytes, which might relate to the aberrant expression of P-cadherin in SCC of the skin.

Human squamous-cell-carcinoma cell line (DJM-1) cells synthesize P-cadherin molecules via an elevation of extracellular calcium: calcium regulates P-cadherin-gene expression at the translational level via protein tyrosine phosphorylation

Spatially-regulated P-cadherin expression is crucial for maintaining the normal epidermal architecture. P-cadherin expression in cutaneous squamous-cell carcinomas (SCC) is altered, and may participate in tumor progression. We therefore investigated how P-cadherin expression was regulated in a cultured cutaneous SCC cell line (DJM-1). At low calcium concentration (0.05 mM), DJM-1 cells expressed P-cadherin weakly in the cytoplasm. At a higher calcium concentration, P-cadherin was promptly translocated to the cell surface within 30 min, gradually increased on the cell surface for up to 48 hr, and was continuously expressed for at least 7 days. During this time course, the total amount of P-cadherin protein had increased, whereas the steady-state mRNA levels for P-cadherin had not changed. The inhibition of protein synthesis by cycloheximide, but not the inhibition of gene transcription by actinomycin-D, completely suppressed the expression of P-cadherin. The effect of calcium was inhibited by tyrphostins but not by H-7, cholera toxin, or dibutylic cyclic AMP. Increments in the extracellular calcium concentration did not mobilize the intracellular calcium pool, and were accompanied by the tyrosine phosphorylation of a 62-kDa protein. In addition, DJM-1 cells expressed mRNA for a calcium-sensing receptor originally demonstrated in the parathyroid gland. The results suggest an unique mechanism for regulating P-cadherin gene expression in DJM-1 cells by extracellular calcium, which stimulates the de novo synthesis of P-cadherin at the translational level through protein tyrosine phosphorylation.