Stephen J. Beebe received a B.S. degree in Zoology from Ohio University, Athens (1970). He then served as a Peace Corps Volunteer in the British West Indies. He than received a PhD in Medical Sciences (Pharmacology) from the Medical College of Ohio, Toledo (1982). He was a Post-Doctoral Fellow in the Howard Hughes Medical Institute and the Department of Molecular Physiology and Biophysics at Vanderbilt University, Nashville, TN. (1982-1986). He was a Fulbright and Marshal Scholar in Department of Medical Biochemistry and the National Hospital in Oslo Norway (1987-88). He returned to the US as an Assistant Professor in Obstetric and Gynecology and then an Associate Professor in the Departments of Pediatrics and Physiological Sciences at the Eastern Virginia Medical School. He is currently a Professor in the Frank Reidy Research Center for Bioelectrics at Old Dominion University, Norfolk VA. For the past 30 years, his research has focused on cell signal transduction with emphasis on expression of and structure-function relationships of the cyclic nucleotide-dependent protein kinases and phosphodiesterases (cAPK, cGPK, and PDEs) [refs 5, 6, 9, 14, 15, 18, 26, 32, 36, 38, 41, 61] and for the regulation of physiological functions including glycogen and lipid metabolism [refs 1-4, 7, 8, 10-12, 16, 17, 25], transcription (refs 13, 49, 72), reproduction [refs 19-23, 27, 30, 31, 37, 39, 52, 57, 65] differentiation and proliferation [refs 24, 28, 40, 42, 44, 53, 56, 73] and pre-embryo genetic diagnosis [refs 33-35]. More recently, his work has focused on cell and tissue responses to nanosecond pulsed electric fields as a means to modulate signal transduction for wound healing and cancer control [refs 43, 45-48, 50, 51, 54, 55, 58-60, 62-64, 66-71, 74-81].
Dr. Beebe was awarded various honors during his career including the Howard Hughes Medical Institute Post doctoral Fellowship, the Fulbright Scholar Award, Oslo, Norway, and the Norwegian Marshall Scholar Award, and Outstanding Senior Visiting Scientist from the Norwegian Research Council. He was also a recipient of the Iwao Yasuda Award for contributions to biomedical research by the Society for Physical Regulation in Biology (2002) and Medicine and the Martin Black Prize from the Institute of Physics and Engineering in Medicine (2005).
Present Research Interests
The effect of ultra short (nanosecond and picosecond), high voltage (kilovolts), pulsed electric fields (nsPEF) on human cells, tissues and tumors: nsPEF are generated by broadband radiofrequencies, a form of non-ionizing electromagnetic radiation. The effects of nsPEF on cells are unique because pulsed electric fields deliver high power (gigaWatts) and low energy (milliJoules) for short durations (nanoseconds, sub-nanoseconds). Using nsPEF with pulse durations shorter and intensities greater than electroporation pulses there is a lower probability for electric field interactions to modify the plasma membrane and a higher probability to modify subcellular structures of human cells. (A) Using fluorescent probes of different molecular weights, flow cytometry, and real time fluorescent microscopy, these studies provide biological assays to prove or disprove theoretical and simulated molecular models for membrane effects of nsPEF on human cells. Under non-lethal conditions, nsPEFs induce transient pores in the plasma membrane that are estimated to be around 1nm, small enough to prevent the entry of propidium iodide or ethidium homodimer-1 into the cell.
Depending on the cell type nsPEF with durations of 10 to 300 nanoseconds and electric fields as high as 300 kV/cm induces apoptosis in human cells. Apoptosis is demonstrated by the coincident appearances of Annexin-V-FITC binding in most cell types, caspase activation, chromosomal condensation, DNA fragmentation and flow cytometric characteristics consistent with cell shrinkage and membrane blebbing. Use of a caspase inhibitor indicates that annexin-binding, but not cell shrinkage and density changes, is caspase-dependent, at least in part. NsPEF provides a novel method to delete diseased (tumors) or unwanted tissues and cells. nsPEF induces apoptosis in mouse fibrosarcoma cells in vitro and mouse tumors ex vivo and in vivo, and melanoma tumors in vivo. NsPEFs can utilize multiple apoptosis pathways including the extrinsic and extrinsic pathway and may or may not use cytochrome c release to initiate apoptosis. Under lethal conditions cell death is coincident with caspase activation. In vivo, nsPEFs can induce apoptosis and cause loss of vascular viability contributing to infarctive tumor death in a temperature-independent manner.
NsPEF induce other cell signaling mechanisms in intact living cells. When nsPEF include electric field intensities below the threshold for apoptosis induction or plasma membrane electroporation, calcium is mobilized from intracellular stores and through store-operated channels in the plasma membrane. This induces human platelet activation, aggregation, and growth factor release. This suggests the potential for wound healing. The potential role for calcium mobilization to modulate other cell functions, such as neurotransmitter release is under investigation. Supported by US Air Force Office of Scientific Research Grant, an EVMS Institutional Grant, and an administrative award from EVMS.
Cyclic AMP Signal Transduction:
This research interest extends to initial research on the roles of cyclic nucleotides in regulation of cell functions. The cyclic AMP-dependent protein kinase (PKA) is the prototype of the protein kinase superfamily, which is one of the largest families encoded by the human genome that plays key roles in regulation of essentially every major eukaryotic pathway from cell division to cell death and everything in between. The PKA is the best defined protein kinase and thereby provides a template for structure and function of all kinases. Having cloned the human catalytic subunit isoforms Ca, Cb and Cg, from a human testes library [ref 26], several years and two NIH grants provided the means to investigate structure function relationships among the isoforms as a means to better understand physical determinants important for function [refs 38, 41, 49, 61, and two others in review]. Through these studies it became clear the Cg was expressed exclusively in primates. Using prokaryotic and eukaryotic expression systems, mutagenesis, substrate specificity and kinetic studies and mass spectroscopy, we defined differences in isozymes substrate and inhibitor specificities, kinetic differences related to structural determinants, and post-translational differences that included the requirement for phosphorylation at threonine 197 for activity in all PKA C-subunit isoforms. We also found that Cg is not only expressed in primate testes, but may be up-regulated during differentiation. Supported by NIH grants (1992-1995 and 1998-2003).