Curcumin exhibits anti-inflammatory and antitumor activities. Although its functional mechanism has not been elucidated so far, numerous studies have shown that curcumin induces apoptosis in cancer cells. In the present study, we show that subtoxic concentrations of curcumin sensitize human renal cancer cells to the tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-mediated apoptosis. This apoptosis induced by the combination of curcumin and TRAIL is not interrupted by Bcl-2 overexpression. We found that treatment with curcumin significantly induces death receptor 5 (DR5) expression both at its mRNA and protein levels, accompanying the generation of the reactive oxygen species (ROS). Not only the pretreatment with N-acetylcystine but also the ectopic expression of peroxiredoxin II, an antioxidative protein, dramatically inhibited the apoptosis induced by curcumin and TRAIL in combination, blocking the curcumin-mediated DR5 upregulation. Taken together, the present study demonstrates that curcumin enhances TRAIL-induced apoptosis by ROS-mediated DR5 upregulation.

Evodiamine is one of the major bioactive compounds that have been isolated and purified from the fruit of Evodiae fructus.

Death receptor DR5 (DR5/TRAIL-R2) is an apoptosis-inducing membrane receptor for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). In this study, we showed that curcumin, a plant product containing the phenolic phytochemical, is a potent enhancer of TRAIL-induced apoptosis through upregulation of DR5 expression. Both treatment with DR5/Fc chimeric protein and silencing of DR5 expression using small interfering RNA (siRNA) attenuated curcumin plus TRAIL-induced apoptosis, showing that the critical role of DR5 in this cell death. Curcumin also induced the expression of a potential pro-apoptotic gene, C/EBP homologous protein (CHOP), both at its mRNA and protein levels. However, suppression of CHOP expression by small interfering RNA did not abrogate the curcumin-mediated induction of DR5 and the cell death induced by curcumin plus TRAIL, demonstrating that CHOP is not involved in curcumin-induced DR5 upregulation. Taken together, the present study demonstrates that curcumin enhances TRAIL-induced apoptosis by CHOP-independent upregulation of DR5.

Mithramycin A is a DNA-binding antitumor agent, which has been clinically used in the therapies of several types of cancer and Paget's disease. In this study, we investigated the combined effect of mithramycin A and tumor necrosis factor-A -related apoptosis-inducing ligand (TRAIL) on apoptosis of cancer cells. In Caki renal cancer cells, which are resistant to TRAIL, cotreatment with subtoxic doses of mithramycin A and TRAIL resulted in a marked increase in apoptosis. This combined treatment was also cytotoxic to Caki cells overexpressing Bcl-2 but not to normal mesengial cells. Moreover, apoptosis by the combined treatment with mithramycin A and TRAIL was dramatically induced in various cancer cell types, thus offering an attractive strategy for safely treating malignant tumors. Mithramycin A -stimulated TRAIL-induced apoptosis was blocked by pretreatment with the broad caspase inhibitor zVAD-fmk or Crm-A overexpression, showing its dependence on caspases. We found that mithramycin A selectively down-regulated XIAP protein levels in various cancer cells. Luciferase reporter assay and the chromatin immunoprecipitation assay using the XIAP promoter constructs show that mithramycin A down-regulates the transcription of XIAP gene through inhibition of Sp1 binding to its promoter. Although XIAP overexpression significantly attenuated apoptosis induced by mithramycin A plus TRAIL, suppression of XIAP expression by transfection with its small interfering RNA prominently enhanced TRAIL-induced apoptosis. We present here for the first time that mithramycin A -induced suppression of XIAP transcription plays a critical role in the recovery of TRAIL sensitivity in various cancer cells.

The skin is a dynamic organ consisting of the dermis and epidermis, with the latter continuously undergoing regeneration to replace cells lost through normal exposure to the environment. The epidermis is composed of several cell layers. The deepest layer, located at the dermal-epidermal junction, is the basal layer, consisting of the undifferentiated basal keratinocytes, which continuously proliferate. As the cells migrate up through the epidermis, keratinocytes undergo a distinct pattern of differentiation that is essential for the function of the skin as a protective barrier. This pattern is characterized by growth arrest and expression of the mature cytokeratins 1 and 10 in the first differentiated layer of the epidermis, the spinous layer. Early differentiation in the spinous layer is followed by late differentiation in the granular layer accompanied by expression of proteins, including the enzyme transglutaminase, that are essential for the formation of the cornified envelope and corneocytes. The corneocytes are terminally differentiated and constitute the outer layer of the epidermis, the cornified layer, which gives skin its resistance to mechanical stresses (for reviews, see Refs. 1 and 2). The mechanism by which 1,25(OH) 2 D 3 inhibits proliferation and stimulates differentiation is still unclear. This hormone is thought to function through the vitamin D receptor, a transcription factor affecting expression of genes possessing vitamin D response elements. However, the keratin 1 gene is the only keratinocyte differentiation marker known to possess a 1,25(OH) 2 D 3 response element (5, 6), and the expression of this marker is inhibited by 1,25(OH) 2 D 3 (7). In addition, 1,25(OH) 2 D 3 was recently shown to enhance the expression of several phosphoinositide-specific phospholipase C isoenzymes (8), the activity of which generates diacylglycerol (DAG). DAG, in turn, is known to regulate the activity of protein kinase C (PKC), and numerous data suggest the involvement of PKC in the regulation of keratinocyte growth and differentiation (reviewed in Refs. 1 and 9).Although PKC-activating DAG can be generated directly by phosphoinositide turnover via phospholipase C, such DAG can also be generated indirectly by an additional pathway. Diacylglycerol is generated by the combination of phospholipase D (PLD), which hydrolyzes phospholipids to generate phosphatidic acid (PA), and PA phosphohydrolase, which dephosphorylates PA to yield DAG (reviewed in Ref. 10). Indeed, in several cell systems, PLD activity has been shown to underlie at least