Leonard R. Johnson, Ph.D.

Leonard R. Johnson, Ph.D. photo

Thomas A. Gerwin Professor
Phone: 901-448-4722
Fax: 901-448-7126
Email: ljohns28@uthsc.edu
Full CV


1963 A.B., Wabash College, Crawfordsville, Indiana
1967 Ph.D., University of Michigan, Ann Arbor, Michigan

Research Interest

Our laboratory has two major projects.  One is focused on the role of polyamines in programmed cell death or apoptosis of the intestinal mucosa.  The other also concerns polyamines and their role in cell migration.  We have shown that polyamines are required for both apoptosis and migration and are currently exploring the signaling pathways involved and the molecular interactions of polyamines that regulate those pathways. 

I am responsible for the gastrointestinal section of the Medical Physiology course.

Current Techniques:

  • cell culture
  • cell migration assays
  • immunohistochemistry
  • stable and transient transfections
  • confocal microscopy
  • electrophoretic mobility shift assays (EMSA)
  • cell cycle analysis

Postdoctoral Fellows: Sujoy Bhattacharya, Ph.D., Shi Jin, M.D., Ph.D., and Bertha Elias, Ph.D.

Research Support

  • NIH RO1 DK 52784-11-15; 9/07 through 8/12; Role of polyamines in early GI mucosal restitution.  $1,472,556 Direct Costs.
  • NIH R37 DK16505-34-44; 4/05 through 3/15 MERIT AWARD; $3,500,000 Direct Costs

Selected Publications

Publications: 2003 -

  1. Du, H., Viar, M.J., Johnson, L.R., and M.A. Watsky. Polyamines in cultured rabbit corneal cells. Invest. Ophthalmol. Vis. Sci. 44:2512-2517, June 2003.
  2. Guo, H., R.M. Ray, and L.R. Johnson. RhoA stimulates IEC-6 cell proliferation by increasing polyamine-dependent Cdk-2 activity. Am. J. Physiol. Gastrointest. Liver Physiol. 285:G704-G713, October 2003.
  3. Bhattacharya S., R.M. Ray, M.J. Viar, and L.R. Johnson. Polyamines are required for the activation of c-Jun NH2-terminal kinase and apoptosis in response to TNF-a in IEC-6 cells. Am. J. Physiol. Gastrointest. Liver Physiol. 285:G980-G991, November 2003.
  4. Bhattacharya, S.R.M. Ray, and L.R. Johnson. Prevention of TNF-a-induced apoptosis in polyamine-depleted IEC-6 cells is mediated through the activation of ERK 1/2. Am. J. Physiol. Gastrointest.Liver Physiol. 286:G479-G490, March 2004.
  5. Zhang, C., D.L. Baker, S. Yasuda, N. Markarova, L. Balazs, L.R. Johnson, G.K. Marathe, T.M. McIntyre, Y. Xu, G.D. Prestwich, H-S. Byun, R. Bittman, and G. Tigyi. Lysophosphatidic Acid Induces Neointima Formation Through PPArg Activation. J. Exp. Medicine. 199:763-774 March 2004.
  6. Johnson, D.A., R.K. Sharma, K. Allan, R. Ray, and L.R. Johnson. Immunochemical localization of polyamines during attachment and spreading of retinal pigment epithelial and intestinal epithelial cells. Cell Mot. Cytoskel. 58:269-280, August 2004.
  7. Poppleton, H.M., F. Edwin, L. Jaggar, R. Ray, L.R Johnson, and T.B. Patel. Sprouty regulates cell migration by inhibiting the activation of Rac1 GTPase. Biochem and Biophysical Res 323:98-103, September 2004.
  8. Deng, W., H. Poppleton, S. Yasuda, N. Makarova, Y. Shinozuka, D. Wang, L.R. Johnson, T.B. Patel, and G. Tigyi. Optimal lysophosphatidic acid-induced DNA synthesis and cell migration but not survival require intact autophosphorylation sites of the epidermal growth factor receptor. J. Biol. Chem. 279:47871-47880, November 2004.
  9. Vaidya, R.J., R.M. Ray, and L.R. Johnson. MEK1 restores migration of polyamine depleted cells by retention and activation of Rac1 in the cytoplasm. Am. J. Physiol. Cell Physiol. 288:C350-C359, January 2005.
  10. Bhattacharya, S., R.M. Ray, and L.R. Johnson. Decreased apoptosis in polyamine-depleted IEC-6 cells depends on Akt-mediated NF-kB activation but not GSK3b activity. Apoptosis 10:759-776, June 2005.
  11. Ray, R.M. Ray, S. Bhattacharya, and L.R. Johnson. Protein phosphatase 2A regulates apoptosis in intestinal epithelial cells. J. Biol. Chem. 280: 31091-31100, September 2005.
  12. Deng, W., M.J. Viar, and L.R. Johnson. Polyamine depletion inhibits irradiation?induced apoptosis in intestinal epithelia. Am. J. Physiol. Gastrointest.Liver Physiol. 289: G599-G606, September 2005.
  13. Bhattacharya, S., R.M. Ray, and L.R. Johnson. STAT3-mediated transcription of Bcl-2, Mcl-1, and c-IAP2 prevents apoptosis in polyamine-depleted cells. Biochem. J. 392: 335-344, November 2005.
  14. Bhattacharya, S., R.M. Ray, and L.R. Johnson. Integrin b3 ? mediated Src activation regulates apoptosis in IEC-6 cells via Akt and STAT-3. Biochem J. 397:437-447, August 2006.
  15. Jin, S., R.M. Ray, and L.R. Johnson. Rac1 mediates intestinal epithelial cell apoptosis via JNK. Am. J. Physiol. 291:G1137-G1147, November 2006.
  16. Vaidya, R.J., R.M. Ray, and L.R. Johnson. Akt-mediated GSK-3 inhibition prevents migration of polyamine-depleted intestinal epithelial cells via Rac1.Cell.Mol.LifeSci. 63:2871-2879, December 2006.
  17. Ray, R.M., R.J. Vaidaya, and L.R. Johnson. MEK/ERK regulates adhernens junctions and migration through Rac1. Cell Mot.Cytoskel.64:143-156, February 2007. Ray, R.M., H. Guo, M. Patel, S. Jin, S. Bhattacharya and L.R. Johnson. Role of myosin regulatory light chair and Rac1 in the migration of polyamine-depleted intestinal epithelial cells. Am. J. Physiol. Gastrointest.Liver Physiol. 292:G983-G995, April 2007.
  18. Deng, W., E. Shuyu, T. Ryoko, W.J. Valentine, G. Durgam, V. Gududuru, L. Balazs, V. Manickam, M. Ausura, L. VanMiddlesworth, L.R. Johnson, A.L. Panill, D.D. Miller, and G. Tigyi. The lysophosphatidic acid type 2 receptor is required for protection against radiation-induced intestinal injury. Gastroenterology 132:1834-1851, May 2007.
  19. Bhattacharya, S., H. Guo, R. Ray, L.R. Johnson. Basic helix-loop-helix protein E47 mediated p21 Waf1/Cip1 gene expression regulates apoptosis of intestinal epithelial cells. Biochem J. 407: 243-247, October 2007.
  20. Ray, R., S. Bhattacharya, L.R. Johnson. EGFR plays a pivotal role in the regulation of polyamine-dependent apoptosis in intestinal epithelial cells. Cell Signal. 19: 2519-2527, December 2007.
  21. Jin, S., R.M. Ray, L.R. Johnson, TNF-a/cycloheximaide-induced apoptosis in intestinal epithelial cells requires RacI-regulated reactive oxygen species. Am. J. Physiol. 294:G928-G937, April 2008.
  22. Bhattacharya, S., R.M. Ray, L.R. Johnson.  Role of polyamines in p53-dependent apoptosis of intestinal epithelial cells.  Cell Signal.  21:509-522, January 2009.