| Andrew R. Marks, M.D.
PROFESSOR OF MEDICINE AND PHARMACOLOGY
Molecular biology of intracellular calcium release channels and their relevence to human disease.
A major focus of the laboratory is the characterization of the single channel properties of the cloned expressed ryanodine receptor (RyR)/calcium release channel of the sarcoplasmic reticulum that controls excitation-contraction (EC) coupling in cardiac and skeletal muscle. Our laboratory reported the physical association between FKBP12 and the ryanodine receptor, and showed that FKBP12 (the cytosolic receptor for the immunosuppressant drugs FK506 and rapamycin which also has cis-trans peptidyl-prolyl isomerase activity) modulates the gating of the channel. Our laboratory has described the abnormal regulation of calcium channel expression during human heart failure We have shown that RyR2 is downregulated and IP3R1 upregulated in human hearts and in several animal models of heart failure. We are currently using animal models of heart failure to test our hypothesis that upregulation of the IP3R plays a role in altering calcium homeostasis by releasing calcium from the ER in response to neurohormonal rather than electrical stimuli. We have reported that the IP3R plays an important role in apoptotic signaling. Long term goals are to determine whether apoptosis plays an important role in human heart failure, and if so what the signals are that trigger apoptosis and whether it can be inhibited possibly by blocking intracellular calcium release via the IP3R or by inhibiting other apoptotic pathways. We have demonstrated the essential role of IP3R1 during antigen-specific T cell activation. We have reported that tyrosine phosphorylation by non-receptor protein tyrosine kinases (NRPTK) of the Src family regulates IP3R during T cell activation. We have shown that T cells made deficient in the type 1 IP3R [by stable expression of antisense IP3R cDNA are resistant to apoptosis induced by T cell receptor (TCR) stimulation, glucocorticoids, ionizing radiation and Fas. Future studies will include identifying signaling events leading to apoptosis that are defective in the IP3R1-deficient T cells. We have shown that an immunosupressant drug, rapamycin, inhibits vascular smooth muscle cell proliferation by blocking regulators of cell cycle progression including cyclin dependent kinases. These observations have lead to studies showing that rapamycin potently inhibits smooth muscle cell migration and restenosis after angioplasty. In addition, we have initiated studies to determine whether rapamycin can inhibit the progression of accelerated arteriopathy in a porcine model of heterotopic cardiac transplantation. We have developed rapamycin resistant muscle cells and demonstrated a defect in regulation of the cyclin-dependent kinase inhibitor p27kip1 in two independent cell lines (inability to upregulate p27kip1 during serum withdrawal or upon rapamycin treatment). These studies have identified a critical role for p27kip1 in the cell growth pathway that is inhibited by rapamycin. Current and future studies are designed to identify the mechanism underlying the defect in p27kip1regulation that is due to degradation via a ubiquitin-independent pathway.
1. Brillantes A-MB, Ondrias K, Scott A, Kobrinsky E, Ondriasova E, Jayaraman, T, Moschella MC, Landers M, Ehrlich BE and Marks AR: Stabilization of calcium release channel (ryanodine receptor) function by FK-506 binding protein. Cell 77:513-523, 1994. Abstract
2. Jayaraman T, Ondrias K, Ondriasova E and Marks AR: Regulation of the inositol 1,4,5-trisphosphate receptor by tyrosine phosphorylation. Science 272:1492-1494,1996. Abstract
4. Marx SO, Reiken S, Hisamatsu Y, Jayaraman T, Burkhoff D, Rosemblit N and Marks AR: PKA phosphorylation dissociates FKBP12.6 from the calcium release channel (ryanodine receptor): Defective regulation in failing hearts. Cell 101:365-376, 2000. Abstract
5. Marx SO, Reiken S, Hisamatsu Y, Gaburjakova M, Gaburjakova J, Yang Y-M, Rosemblit N and Marks AR: Phosphorylation-dependent regulation of ryanodine receptors: A novel role for leucine/isoleucine zippers. J. Cell Biol. 153:699-708, 2001. Abstract PDF file