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Loricrin is a major component of the epidermal cornified cell envelope and is expressed only in terminally differentiated keratinocytes. This cell differentiation-specific expression pattern suggests specific regulatory mechanisms for activation of loricrin gene transcription in differentiated keratinocytes. Here, we identified a positive regulatory element in the proximal promoter region of the loricrin gene involved in activation of its expression in differentiated keratinocytes. A database search indicated that this sequence contained a GATA-3 binding motif. Constructs with point mutations in the GATA-3 binding motif showed decreased reporter activity, indicating that GATA-3 positively regulates loricrin gene transcription. Western blotting analysis indicated that GATA-3 is more abundant in differentiated than in undifferentiated keratinocytes. Cotransfection experiments indicated that GATA-3 activates transcription of the loricrin gene in a cooperative manner with c-Fos and Sp1. These findings indicate that GATA-3 contributes to keratinocyte differentiation-specific activation of loricrin gene transcription via interaction with c-Fos and Sp1. [ABSTRACT FROM AUTHOR]

Previous studies of epidermal-specific gene promoters suggested that a limited set of transcription factors regulate keratinocyte-specific and differentiation-specific gene expression in the epidermis. In the present study, we investigated the functional importance of AP-1- and Sp1-binding elements in the determination of cell type-specific and differentiation-specific gene expression by transient transfection into undifferentiated and differentiated keratinocytes as well as into various non-epidermal cell lines. Synthesized short AP-1- and/or Sp1-binding elements were inserted into a minimal reporter vector, and the artificial promoter containing both AP-1 and Sp1 elements showed high levels of transcriptional activity only when transfected into differentiated keratinocytes. Promoters containing either the AP-1 or the Sp1 motif alone showed little activity in any of the cells examined. We also found that close proximity of the Sp1 and AP-1 sites is essential for transcriptional activity, suggesting that the physical interaction between Sp1 and AP-1 factors is important for functional activity. These results clearly demonstrate that the combination of ubiquitously expressed transcription factors AP-1 and Sp1 confers keratinocyte specificity and differentiation specificity on the gene expression. Our findings also provide a simple model of the mechanisms underlying regulation of cell type-specific and cell differentiation-specific gene expression by ubiquitously expressed transcription factors. [ABSTRACT FROM AUTHOR]

Presents a study conducted for the immunohistochemical detection of erbB-4 expression in extramammary Paget's disease. Characteristics of the occurrence of the disease; Clinical features of extramammary Paget's disease patients; Immunohistochemical staining of the erbB-4.

Proliferation and differentiation in the epidermis must be tightly regulated. This regulation is known to involve a range of transcription factors, including pituitary tumor transforming gene 1 (PTTG1), a ubiquitously distributed transcription factor that regulates keratinocyte proliferation and differentiation. Psoriasis is a common but refractory skin disorder, the pathophysiology of which is characterized by hyperproliferation and impaired differentiation in the epidermis. The present study was conducted to clarify the less well-known roles of PTTG1 in the pathophysiology of psoriasis, focusing on its relationship with tumor necrosis factor-α (TNF-α), which is a critical mediator of the disease. The levels of PTTG1 expression were increased in the psoriatic epidermis. Overexpression of PTTG1 resulted in the overproduction of TNF-α, and TNF-α itself had an inductive effect on PTTG1 expression, suggesting that their expression may involve autoinduction. Moreover, overexpression of PTTG1 involved augmented the expression of cyclin A and B1 proteins in both cultured keratinocytes and the psoriatic epidermis. Therefore, enhanced expression of PTTG1 in the psoriatic epidermis may result in aberrant regulation of the cell cycle and impaired differentiation via the interplay between PTTG1 and TNF-α. [ABSTRACT FROM AUTHOR]

The epidermis is a self-renewing tissue, the homeostasis of which is dependent upon the tight balance between proliferation and differentiation based on appropriate regulation of the cell cycle. The cell cycle regulation is dependent on the interactions among a number of cell cycle regulatory molecules, including the pituitary tumor-transforming gene 1 (PTTG1), also known as securin, a regulator of sister chromatid separation and transition from metaphase to anaphase. This study was conducted to clarify the less-known functions of PTTG1 in the epidermis by the use of keratinocytes cultured under two-dimensional (2D) or three-dimensional (3D) conditions. Forced overexpression of PTTG1 caused upregulation of cyclin B1, cyclin-dependent kinase 1 (CDK1), and c-Myc, resulting in enhanced proliferation and suppression of early differentiation without apparent alterations in terminal differentiation, and the exogenous PTTG1 was downregulated in association with cell cycle exit. In contrast, depletion of PTTG1 caused their downregulation and constrained proliferation with retention of differentiation capacity. These findings suggested that PTTG1 could alter the proliferation status by modulating the expression levels of the other cell cycle regulatory proteins, and excess PTTG1 primarily affects early differentiation of keratinocytes under the stability regulation associated with cell cycle exit. [ABSTRACT FROM AUTHOR]

Loricrin is a major component of the epidermal cornified cell envelope, and is expressed only in terminally differentiated keratinocytes. This cell differentiation-specific expression pattern suggests specific suppression of loricrin gene expression in undifferentiated keratinocytes as well as its activation in differentiated keratinocytes. We identified a negative regulatory sequence element in the first intron of the mouse loricrin gene involved in suppression of loricrin gene expression in undifferentiated keratinocytes. A database search indicated that this sequence contained the putative inverted Yin-Yang 1 (YY1)-binding motif. Constructs with point mutations in the putative YY1-binding motif showed increased reporter activity, indicating that YY1 negatively regulates loricrin gene transcription. Co-transfection experiments using a YY1 expression vector revealed that YY1 represses loricrin promoter activity. Western blotting and immunohistochemical analyses indicated that YY1 is more abundant in undifferentiated than in differentiated keratinocytes. These findings suggest that YY1 contributes to specific loricrin gene expression in differentiated keratinocytes by suppression of its transcription in undifferentiated keratinocytes. Furthermore, we demonstrated that forced expression of YY1 in differentiated keratinocytes results in specific downregulation of expression of other early and late differentiation markers. [ABSTRACT FROM AUTHOR]