In order to analyze the hormonal effects of dehydroepiandrosterone (DHEA) in skin sebaceous glands, the precursor steroid was administered to ovariectomized (OVX) female Sprague-Dawley rats at a dose of 30 mg applied on the dorsal skin, twice daily, for 3, 6 and 12 months. In a parallel experiment, female OVX rats were treated with DHEA at the same daily percutaneous dose of 30 mg, alone or in combination with the antiandrogen Flutamide or the pure antiestrogen EM-800, for 12 months, in order to determine the androgenic and/or estrogenic components of DHEA action. Treatment of female OVX rats with DHEA resulted in a similar mild to moderate hyperplasia of the sebaceous glands of both dorsal (site of application) and ventral skin, as illustrated by an increase in the number and size of the acini. The above-indicated effects were observed at all time intervals studied, beginning at 3 months of treatment, and they were not further increased after longer term administration of DHEA (for 6 and 12 months). The addition of Flutamide to DHEA treatment completely prevented the DHEA-induced changes in the sebaceous glands, whereas the antiestrogen EM-800 had no effect. The present data indicate an exclusive androgenic stimulatory action of DHEA on the sebaceous glands, thus pointing out the importance of local intracrine DHEA transformation into androgens for skin anatomical integrity and function, while showing that estrogens, if active in rat skin, do not originate from DHEA.

CYP24 is a well-established vitamin D receptor (VDR) target gene. The active VDR ligand 1,25(OH)₂D₃ regulates its own catabolism by increasing CYP24 expression. It is well known that in the presence of 1,25(OH)₂D₃, VDR binds to VDREs in the promoter region of CYP24 and initiates CYP24 transcription. However, little is known about the role of 1,25(OH)₂D₃ in the posttranscriptional modulation of CYP24. In this study, we investigated the functional significance of 1,25(OH)₂D₃ in CYP24 RNA splicing in colon cancer cells. Using RT-PCR, we found that 1,25(OH)₂D₃ actively induces CYP24 splicing in a time-dependent manner and CYP24 splicing pattern could be cell type or tissue specific. The induction of RNA splicing by 1,25(OH)₂D₃ was mainly CYP24 selective. Treatment of cells with parathyroid hormone inhibited basal CYP24 splicing, but failed to inhibit 1,25(OH)₂D₃-induced CYP24 splicing. Further experiments demonstrated that new RNA synthesis was required for the induction of CYP24 splicing by vitamin D. In addition, alteration of multiple signaling pathways also affected CYP24 splicing and cellular sensitivity in response to vitamin D appeared to correlate with the induction of CYP24 splicing. These results suggest that 1,25(OH)₂D₃ not only regulates CYP24 transcription, but also plays an important role in posttranscriptional modulation of CYP24 by inducing its splicing. Our findings reveal an additional regulatory step that makes the vitamin D mediated action more prompt and efficient.

Cultured primary human keratinocytes were the first non-cancer-derived cell type reported to produce the humoral hypercalcemia factor, parathyroid hormone-related protein (PTHrP). Emerging evidence suggests that only a subset of keratinocytes produce high levels of PTHrP in vivo. We found that the PTHrP mRNA content of intact human skin was minimal, whereas transcripts were easily detectable in primary keratinocytes derived from those skin samples. We hypothesized that conditions associated with growth in culture activated PTHrP gene expression in primary keratinocytes. In culture, keratinocytes produce a number of epidermal growth factor (EGF)-like ligands (transforming growth factor-alpha, heparin binding-EGF and amphiregulin) and their receptor, ErbB1. Treatment of keratinocytes with a specific erbB1 inhibitor (PD153035) reduced PTHrP mRNA levels by >80% in rapidly growing keratinocytes. Treatment of keratinocytes with reagents that neutralize amphiregulin reduced PTHrP mRNA levels by approximately 60%. Blockade of erbB1 signaling reduces transcription from the endogenous PTHrP P3-TATA promoter. The Ets transcription factor-binding site, 40 bases upstream of the P3 promoter, is required for baseline expression of PTHrP reporter gene constructs in keratinocytes; in addition, cotransfection of Ets-1 and Ets-2 expression vectors activate the reporter gene constructs. Finally, disruption of both ras and raf signaling reduce reporter gene expression by 80%, suggesting that ErbB1 signaling is mediated by the classic ras/MAP kinase pathway. These findings suggest that acquisition of EGF-like ligand expression has the potential to substantially activate PTHrP gene expression in the epidermis.