SESSION 4: SITE-SPECIFIC MODIFICATIONS OF CELL SIGNALING PROTEINS BY SULFHYDRYL SWITCHES Can Diet Modify Cell Proliferation Through Sulfhydryl Switches on Transcription Factors? David Gius, National Institutes of Health Can Dietary Factors Regulate Activity of Cell Signaling Proteins Through Sulfhydryl Biochemistry? Catherine A. O’Brian, University of Texas, M.D. Anderson CC How Can Non-Thiol Dietary Components Cause Thiol Regulation of the Cell Cycle? Chung S. Yang, Rutgers University David Gius, M.D., Ph.D., Section Chief, Molecular Radiation Oncology, Radiation Oncology Branch, NCI, NIH, took us inside the nucleus, to consider the role that redox regulation plays in regulating immediate early genes and transcription factors that are constitutively upregulated in tumor cells because they up-regulate proliferation and pro-survival. Catherine A. O’Brian, Ph.D., Professor, Department of Cancer Biology, University of Texas M.D. Anderson Cancer Center, Houston, discussed enzymes belonging to the protein kinase C family that are regulated by glutathiolation, and the potential for influence of diet on these sulfhydryl switches. Chung S. Yang, Ph.D., Professor and Chair, Department of Chemical Biology, Ernest Mario School of Pharmacy, Rutgers University, Piscataway, New Jersey, broadened our perspective by discussing non-thiol dietary components that may perturb thiol regulation of the cell cycle. In response to oxidative stress, a series of immediate early response genes, including the oncogenes c-fos and c-jun are upregulated, resulting in enhanced expression of the pro-proliferation transcription factor AP-1, a heterodimer of Fos and Jun. Both AP-1 and the signaling factor redox factor-1 Ref-1 contain redox-sensitive cysteines that may regulate their activities in response to oxidative stress: specifically, it appears that the binding of AP-1 to DNA is redox-sensitive. Similarly, both thioredoxin reductase and thioredoxin bear cysteine-rich redox-sensitive domains. Transfection and overexpression of thioredoxin reductase enhances AP-1 binding, whereas inhibition of thioredoxin reductase interrupts this activation. Furthermore, overexpression of a mutant thioredoxin reductase that was missing these redox-sensitive cysteines, was without effect. Thioredoxin reductase may therefore be intimately involved in the response of these factors to oxidative stress, possibly through reduction of thioredoxin, which may then translocate into the nucleus to combine with Ref-1 in supporting AP-1 binding. These redox-sensitive signaling proteins may play an integral part in the balance between pro-oxidant and anti-oxidant systems, directing the cell toward survival/DNA repair or apoptosis, following oxidative damage. The mechanism whereby oxidative stress triggers reduction of thioredoxin reductase and Ref-1, remains speculative, but may involve an enhancement of NADPH generation. Members of the protein kinase C (PKC) family mediate tumor promotion and progression. They contain between 16 and 28 cysteine residues, and are regulated by glutathiolation. Redox regulation of the different isoforms of PKC shows that, at least in this system, glutathiolyation can inactivate one protein, whereas an opposing isoenzyme was resistant to loss of activity due to glutathiolation. When cells were placed under oxidative stress by including diamide in the medium, glutathiolation of PKC occurs. Specifically, PKCä, an enzymes that normally inhibits promotion, did not lose activity when glutathioloated, whereas PKCĺ, an enzyme whose activity is to enhance promotion, was inhibited by glutathiolation. Thus glutathiolation inhibits PKC-dependent promotion. This action of glutathione to switch off promotion has been modeled ex vivo, in cell culture, as well as in whole mice, using diamide, cystamine or cystine, and NAC was able to reverse this. It will be interesting to see if dietary thiol-containing and thiol-reactive compounds that are associated with prevention of carcinogenesis, such as allyl sulfides and isothiocyanates, can also trigger these changes in PKC activity in mice. Tea polyphenols, including the major component epigallo catechin gallate (EGCG) have both antioxidant and anticarcinogenic activity. However, as with so many dietary antioxidants with possible anticarcinogenic activity, whether there is a relationship between antioxidant and anticarcinogenic activity is not known at this time. There are a number of theories based on quenching of reactive oxygen species, but these have not been proven and, at least in cell culture, EGCG appears to have its pro-apoptotic effects when acting as a prooxidant. EGCG addition to cell culture causes production of peroxide, and catalase inhibits EGCG-induced apoptosis of H661 human lung cells. It is not known if EGCG acts in this pro-oxidant fashion in vivo. NIH, August 2003 Remember we are NOT Doctors and have NO medical training. This site is like an Encylopedia - there are many pages, many links on many topics. Support our work with any size DONATION - see left side of any page - for how to donate. You can help raise awareness of CAM.