Mechanisms of 1,25-dihydroxyvitamin D3 regulation of vitamin E succinate mediated apoptosis in a multistage carcinogenesis model
Abstract
The purpose of this work was to determine how 1,25(OH)2D 3 protects C3H10T½ cells from vitamin E succinate (VES)-mediated apoptosis. 1,25(OH)2D3 does not protect C3H10T½ cells stably transfected with the H-ras oncogene (rasneo11A cells). Therefore, understanding the mechanisms through which 1,25(OH) 2D3 protects “normal” C3H10T½ cells could contribute to the use of 1,25(OH)2D3 as a co-treatment to chemotherapeutic drugs. Initial studies utilized C3H10T½ and rasneo11A cells to determine the effects of 1,25(OH)2D 3 on genomic signaling in both “normal” and H-ras transfected cells. Although both cell types express the vitamin D and retinoid X receptors (VDR & RXR) in similar amounts, rasneo11A cells showed a significant attenuation in luciferase reporter response to 1,25(01-1) 2D3. Activation of H-ras results in increased activation of extracellular regulated kinase (ERK) in most cell lines, including C3H10T½. Further study into the effects of ERK on 1,25(OH)2D 3 signaling revealed that this pathway is not responsible for the attenuated response to 1,25(OH)2D3 in rasneo11A cells. The focus of this study then concentrated on the response of C3H10T½ cells to 1,25(OH)2D3. Nuclear factor κB (NFκB), ERK and phosphatidylinositol 3 kinase (PI3K) are all implicated as pro-survival pathways induced by a variety of mitogenic factors. Stress activated protein kinase (SAPK) is a member of the mitogen activated protein kinase (MAPK) family that is activated in response to stress and death signals. The balance between ERK (also a MAPK member) and SAPK can be regulated through MAPK phosphatase-1 (MKP1). Our hypothesis is that 1,25(OH)2D3 activates two pathways that cooperatively lead to cell survival: PI3K-NFκB and ERK-NFκB. Additionally, the balance between ERK and SAPK is tipped toward the pro-survival ERK through the activity of MKP1 We have demonstrated that both the PI3K and ERK pathways are essential to the activation of NFκB by 1,25(OH)2D3. Prevention of NFκB activation resulted in inhibition of the protective response elicited by 1,25(OH) 2D3 in C3H10T½ cells treated with VES. The activity of MKP1 was also necessary to protection from VES by 1,25(OH)2D 3, as cells transfected with a dominant negative MKP1 construct underwent apoptosis in the presence of VES and 1,25(OH)2D3 together. Therefore, the PI3K and MAPK pathways are both implicated in 1,25(OH) 2D3-mediated protection from apoptosis in C3H10T½ cells.
Degree
Ph.D.
Advisors
Teegarden, Purdue University.
Subject Area
Nutrition|Cellular biology
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