Poster Topical Area: Dietary Bioactive Components
Location: Hall D
Poster Board Number: 381
Liver kinase B1 (LKB1) is a tumor suppressor protein and calcium calmodulin kinase kinase-2 (CaMKK2) is pro-tumorigenic and is overexpressed in many cancers. Activation of LKB1 is mediated by the activity of protein kinase C-zeta (PKCzeta), while inhibition of CaMKK2 occurs following phosphorylation at Ser511 by death associated protein kinase (DAPK). DAPK activation appears to be an important and universal inhibitor of the proliferation and promotion of a variety of cancers. Simultaneously, but antithetically, regulating these signaling proteins (LKB1 and CaMKK2) would be a tremendous advancement in the treatment of cancer.
Objective: The objective was to determine if a well-defined blend of 10 herbal extracts that has been successful in a variety of clinical trials could simultaneously regulate the activity of these two proteins.
Methods: Upstream mediators (i.e., PKCzeta and DAPK), downstream targets (i.e., AMPK) and both kinases (i.e., LKB1 and CaMKK2) were modulated using pharmacologic and molecular techniques in several cancer cell lines.
Results: The PHB increased the phosphorylation of PKCzeta, resulting in its translocation to the nucleus where it phosphorylated (Ser428) and activated LKB1. pLKB1 translocated to the cytosol where it activated the tumor suppressor protein AMPK. Activation of AMPK resulted in suppression of cell proliferation. CaMKK2 was simultaneously inhibited in the presence of the PHB via phosphorylation at Ser511 mediated by DAPK. These results were verified in the presence of chemical inhibitors (radicicol, STO-609, EGTA, BAPTA-AM, DAPK inhibitor, PKCzeta pseudosubstrate inhibitor), knockdown experiments using siRNA techniques, and using a LKB1-null cell line that overexpresses CaMKK2, ± the insertion of a wild-type LKB1 construct or catalytically dead mutants of LKB1.
Conclusion: This PHB simultaneously, and antithetically, regulated two parallel signaling pathways known to be important in cancer. This is the first paper in the literature to report this kind of concurrent action either pharmacologically or with natural food products, and suggests that some natural products may have an advantage in cancer treatment because of their simultaneous multiple targets of action.
Professor and Head
University of Tennessee