Alpha Omega Alpha Honor Medical Society

Univerity of California, Irvine College of Medicine

The Zeta Chapter of the Alpha Omega Alpha Honor Medical Society

Student Research Fellowship Recipients

Recipient in 1995: Hung Bryant Nguyen

Intracellular Calcium in Growth Factor Signal Transduction Pathways

While working in the Department of Physiology & Biophysics at UC Irvine, under the mentorship of Dr. Jay Gargus, MD, PhD, the AOA Research Fellowship awarded to Mr. Nguyen contributed in five publications (3 abstracts and 2 peer-reviewed manuscripts) in the area of intracellular calcium signal transduction:

Publications

  1. Estacion M, Nguyen HB, Gargus JJ. Calcium is permeable through a maitotoxin-activated nonselective cation channel in mouse L-cells. Am J of Physio 1996;270:C1145-52.
  2. Nguyen HB, Estacion M, Gargus JJ. Mutations causing achondroplasia and thanatophoric dysplasia alter bFGF induced calcium signals in human diploid fibroblasts. Hum Mol Gen 1997;6: 681-9.
  3. Gargus JJ, Estacion M, Nguyen HB. Novel biophysical technique to detect congenital disease: detection of inborn errors in FGF signaling. Amer J of Hum Gen 1996;59:A198 (abstract).
  4. Nguyen HB, Estacion M, Gargus JJ. Mutations causing achondroplasia and thanatophoric dysplasia alter bFGF induced calcium signals. FASEB J. 1996;10:A421 (abstract).
  5. Nguyen HB, Estacion M, Gargus JJ. PDGF-stimulated intracellular calcium signals in single mouse L-cells. Mol Cell Bio 1994;5:258a (abstract).

Briefly, his role in the first manuscript is to apply ratiometric imaging of intracellular calcium using the indicator dye Fura-PE3 in identifying calcium influx through a PDGF-activated nonselective cation channel in mouse L-cells (a NS channel previously identified in Dr. Gargus' lab). The importance of the paper is that this NS channel may also be sensitive to the shellfish poison maitotoxin (MTX) since MTX irreversibly activates a nonselective cation channel that shares many of the features of the NS channel. A rise in intracellular calcium in response to MTX secondarily activates a calcium-activated outward potassium current that is endogenous to these cells (supported by a concurrent whole-cell patch-clamp study performed by M. Estacion in the lab). The finding suggests that this current can be used as a biosensor of the calcium concentration at the inner face of cell membrane. The fenamate class of NSAID, such as flufenamic acid, mefanamic acid, and 3',5'-dichlorodiphenylamine-2-carboxylic acid, which the lab has previously shown to reversibly block the NS channel, however, does not block the MTX-activated calcium influx. This finding suggests that MTX irreversibly locks the NS channel into an open state that is unblockable by the fenamate binding site. The fact that the fenamate class does not block calcium influx through the NS channel is contrary to their expectation since the original hypothesis was that the fenamate would prevent an increase in intracellular calcium and thereby block proliferation. Unpublished data show that the fenamate may even cause a rise in intracellular calcium in addition to blocking the NS channel and proliferation. Thus the interplay between calcium signaling and cell cycle may be much more complicated than what the literature suggests.

In order to apply calcium imaging in clinical diagnosis, the second publication showed that homozygous achondroplasia (Ach) cell lines carrying a specific fibroblast growth factor receptor 3 (FGFR3) mutation fail to signal intracellular calcium in response to basic fibroblast growth factor (bFGF). However, heterozygous Ach cells responded normally with an increase in intracellular calcium. The thanatophoric dysplasia TD1 heterozygous cells were unresponsive to bFGF, whereas the TD2 heterozygotes produced normal calcium response. These findings suggest a clinical role for calcium imaging technique that may complement existing prenatal genetic screening of developmental defects.

To further develop his research background in intracellular signal transduction, Mr. Nguyen received the NIH Intramural Research Fellowship and Training Award. He joined Dr. James Russell's lab at the National Institute of Child Health and Human Development in 1995. With the funding, he gained training in the technique of cell patch-clamping in order to help characterize a calcium activated K+ channel in pinealocytes. His contribution resulted in an abstract publication:

  1. Darvish N, Nguyen HB, Neale E, Russell JT. PACAP activates a novel non-selective cation channel in rat pineal cells. Soc for Neurosci 1996;22:1027 (abstract).

For his contribution in research during medical school, Mr. Nguyen also received the Vincent P. Carroll Memorial Outstanding Research Award.