Modulation of Apoptosis in HaCaT Keratinocytes via Differential Regulation of ERK Signaling Pathway by Flavonoids

Abstract

The exact molecular mechanisms underlying the cellular effects associated with various flavonoids have yet to be fully explained. In the present study, we have administered several flavonoids to human HaCaT keratinocytes and determined that 3,4-dihydroxy flavone (3,4-DHF) exerts a slight stimulatory effect on cell growth, although other flavonoids, including kaempferol, quercetin, and isorhamnetin, exhibited growth inhibitory properties. 3,4-DHF was found to exert an anti-apoptotic effect on etoposide-induced cell death of HaCaT keratinocytes. We were also able to determine that sustained ERK activation was intimately associated with the etoposide-induced apoptosis of HaCaT cells, and treatment with 3,4-DHF induced a significant suppression of etoposide-induced ERK activation, concomitant with the repression of poly(ADP-ribose) polymerase or the cleavage of pro-caspase 3. ERK overexpression significantly overrode the anti-apoptotic function of 3,4-DHF, but this was not true of ERK-DN. Moreover, treatment with 3,4-DHF resulted in the protection of cells from H 2 O 2 -induced cell death and exerted an apparent suppressive effect on the stress-induced generation of reactive oxygen species (ROS). Finally, we showed that 3,4-DHF almost completely abolished kaempferol-induced apoptosis, coupled with a concomitant suppression of both intracellular ROS generation and the activation of ERK. Taken together, our data clearly indicate that a host of phytochemicals, including etoposide and a variety of flavonoids, differentially regulate the apoptosis of human HaCaT keratinocytes via the differential modulation of intracellular ROS production, coupled with the concomitant activation of the ERK signaling pathway. According to these results, we are able to conclude the distinct structureactivity relationship between several flavonoids.

Lysophosphatidic acid prevents apoptosis of Caco-2 colon cancer cells via activation of mitogen-activated protein kinase and phosphorylation of Bad

“…Previous studies have shown that etoposide-induced apoptosis of fibroblasts and keratinocytes is associated with an increase in Erk phosphorylation [51,52]. In fibroblasts, etoposide induced caspase activity, which was completely abrogated by inhibition of Erk activity [51,52]. In keeping with these reports, apoptosis of hepatocytes by Clostridium difficile toxin is accompanied by acute stimulation of Erk [53].…”

“…On the other hand, etoposide alone resulted in acute phosphorylation of Erk at 30 min and occasionally weak and delayed Erk phosphorylation at 12-24 h ( Figure 7A). Previous studies have shown that etoposide-induced apoptosis of fibroblasts and keratinocytes is associated with an increase in Erk phosphorylation [51,52]. In fibroblasts, etoposide induced caspase activity, which was completely abrogated by inhibition of Erk activity [51,52].…”

trans-Resveratrol induces apoptosis in human breast cancer cells MCF-7 by the activation of MAP kinases pathways

“…The involvement of ROS has been proposed as upstream event occurring during treatment with high (micro-molar) concentrations of trans-resveratrol [1,21], as well as with other polyphenols, including epigallocatechin-3-gallate [44,53), woodfordin I [35] and quercetin [33,64]. In our experimental system ROS burst occurs precociously (within the first hour) and the detrimental effects produced were confirmed by the increase in lipid peroxidation by-products, MDA and 4-HNE.…”

Inhibitory effects of flavonoids on TNF-α-induced IL-8 gene expression in HEK 293 cells

“…4A). TNF-α is pleiotropic pro-inflammatory cytokine that is produced by a wide range of activated cells (1,8). TNF-α stimulation results in the activation of IKK, which then phosphorylates IκBα at serine 32 and 36.…”

“…These multiple biological activities have resulted in flavonoids gaining attention as potentially useful therapeutics for a variety of diseases such as cancer, cardiovascular diseases, autoimmune diseases and infectious diseases (7). However, despite the diverse beneficial biological and pharmacological effects of flavonoids, their use for the treatment of human diseases is not popular due to their high effective concentrations and poor absorptive effects and because their detailed molecular mechanisms have not yet been elucidated (7,8). Therefore, better understanding of their activities, action mechanisms and interaction with other compounds is necessary (7,9).…”