The Role of VDA Phosphorylation in Vitamin D Induced Apoptosis
Abstract
Vitamin D compounds are currently in clinical trials for human breast cancer and offer an alternative approach to anti-hormonal therapies for this disease. 1,25-Dihydroxyvitamin D3 (1,25-D3), the active form of vitamin D3, acts through the nuclear vitamin D receptor (VDR) and is a potent negative growth regulator of breast cancer cells. Studies were initiated to examine the phosphorylation state of the VDR in relation to apoptosis. These studies involved immunoprecipitation of the VDR from MCF-7 cells treated with 1,25-D3 or TPA, a protein kinase C activator. This technique yielded inconclusive data due to low VDR abundance coupled with non-specific antibody binding. Additional methods, including use of antibody affinity columns are now being developed for this project. To determine whether phosphorylation pathways influence vitamin D signaling downstream of the VDR, we have focused on identification of specific intracellular events involved in 1,25-D3 mediated apoptosis such as the effects of 1,25-D3 on mitochondrial function and caspase activity. The major findings are that 1,25-D3 induces apoptosis in MCF-7 cells by disrupting mitochondrial function which is accomplished by translocation of Bax to mitochondria, release of cytochrome C, and induction of reactive oxygen species production. The effect of 1,25-D3 signaling on mitochondria does not require caspase activation, since caspase inhibitor (zVAD.fink) was unable to block these events. Although caspase inhibitor was able to block events downstream of mitochondria such as PARP cleavage, external display of phosphatidylserine, and DNA fragmentation, the commitment of MCF-7 cells to 1,25-D3 mediated cell death is caspase independent.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 1999
- Accession Number
- ADB252893
Entities
People
- Carmen J. Narvaez
Organizations
- University of Notre Dame