Associated Faculty
  Internal Users

home >> people >>
Leda Raptis


  Contact Information:  
  Professor of Microbiology and Immunology

Tel: (613) 533-2462
Fax:(613) 533-6796
email: raptisl@post.queensu.ca

  The DNA tumor viruses polyoma and SV40 are among the most studied models of viral oncogenesis. My research interests include the elucidation of the mechanism of transduction of transforming signals from the tumor genes of these viruses. I am using two different approaches:

1. Downregulation of expression of specific cellular genes through the introduction of an anti-message or dominant-negative mutants, to demonstrate the overall involvement of a gene product.

2. Introduction of peptides corresponding to the proteins' point(s) of contact, using a novel apparatus, to more specifically pinpoint the areas involved.

The cellular Ras proteins have long been suspected of transducing proliferative signals from membrane protein-tyrosine kinases. This was definitively demonstrated by expressing the membrane-bound, middle tumor antigen of polyoma virus (mT), in cells where Ras levels were reduced through the introduction of a ras-antisense construct, the transcripts from which block Ras protein translation by forming a dsRNA. More recent results suggested that, aside from mT, the main tumor protein of the Simian virus 40 virus (SVLT) requires the action of the cellular Ras proteins, thereby suggesting the exciting possibility that, although primarily nuclear, SVLT requires this membrane function in order to transform.

The reduction in the activity of a signal transducer as above can demonstrate its overall involvement in the transmission of a signal. To further examine its role, it is imperative to more finely pinpoint the in vivo interactions of different areas of the protein with other members of the cascade. To achieve this, we developed a new technique, termed electroporation in situ. Peptides are introduced corresponding to the proteins' points of contact in order to specifically block their interaction. Recent results demonstrated the exquisite ability of this technique to distinguish between closely related signals and open new avenues for the development of peptidomimetic drugs.

  SV40 protocols. Editor: L. Raptis. Methods in Molecular Biology series, Humana Press Inc, 2001.

Grammatikakis, N., Jaronczyk, K., Vultur, A., Grammatikakis, A., Brownell, H.L. Benzaquen, M., Rausch, C., Lapointe, R. and Raptis, L. 2001. Simian Virus 40 large Tumor antigen interacts with and modulates the Raf signalling pathway. J. Biol. Chem. 276:27840-27845.

Raptis,L. and Vultur, A. 2001. Neoplastic transformation assays. Chapter 11, pages 153-166. In: Methods in Molecular Biology. SV40 Protocols. Raptis L. ed. The Humana Press Inc., Totowa, NJ.

Brownell, H.L. and Raptis, L. 2001. [a32P]GTP electroporation for the measurement of Ras activation by SVLT. Chapter 16, pages 221-230. In: Methods in Molecular Biology. SV40 Protocols. Raptis L. ed. The Humana Press Inc., Totowa, NJ.

Qiao, H., R. Saulnier, A. Patryzkat, N. Rahimi, L. Raptis, J. Rossiter, E. Tremblay, and B. Elliott. 2000. Cooperative effect of Hepatocyte Growth Factor and fibronectin in anchorage- independent survival of mammary carcinoma cells: Requirement for phosphatidylinositol-3 kinase activity. Cell Growth Differ. 11:123-133.

Liu, Q-Y, Carson, C., Ribecco, M., Testolin, M., Raptis, L., Walker, P.R. and Sikorska, M. 2000. Effects of neoplastic transformation and Teniposide (VM26) on PKC isoform expression in rodent fibroblasts. Cancer Lett. 153:13-23

Raptis,L., H. L. Brownell, A. Vultur, G. Ross, E. Tremblay and B. Elliott. 2000. Specific inhibition of Growth Factor-stimulated ERK1/2 activation in intact cells by electroporation of a Grb2-SH2 binding peptide. Cell Growth Differ. 11:293-303.

Raptis, L., Firth, K.L. Tomai, E. and Forkert, P.G. 2000. Improved procedure for examination of gap junctional, intercellular communication by in situ electroporation on a partly conductive slide. Biotechniques, 29:222-226.

Tomai, E., Klein, S., Firth, K.L. and Raptis, L. 2000. Growth on Indium-Tin oxide-coated glass enhances 32P-phosphate uptake and protein labelling of adherent cells. Prep. Biochem. Biotechnol. 30:313-320.

Li, G. Szewczuk, M.R., Raptis, L. Johnson, J.G. Weagle, G.E. Pottier, R.H. and Kennedy, J.C. 1999. Rodent fibroblast model for studies of response of malignant cells to exogenous 5-amino- levulinic acid. Brit. J. Cancer, 80:676-684.

Tomai, E., H.L. Brownell, T. Tufescu, K. Reid, B.G. Campling, and L. Raptis. 1999. Gap junctions in lung carcinoma cells. Lung Cancer, 23:223-231.

Raptis, L., H.L. Brownell, K.L. Firth and S. Giorgetti-Peraldi. 1998. In situ electroporation for the study of signal transduction, J.C. Celis (ed.), Cell Biology: A laboratory handbook. Academic Press Inc., Volume 4:75-87.

Brownell, H.L. and Raptis, L.. 1998. Electroporation of nucleotides. Assessment of Ras activity. 32P-labelling of cellular components, J.C. Celis (ed.), Cell Biology: A laboratory handbook. Academic Press Inc., Volume 4:65-74.

Brownell, H.L., N. Lydon, E. Schaefer, T.M. Roberts, and L. Raptis. 1998. Inhibition of Epidermal Growth Factor-mediated ERK1/2 activation by in situ electroporation of nonpermeant [(alkylamino)methyl]acrylophenone derivatives. DNA Cell Biol. 17:265-274.

Tomai, E., H.L. Brownell, T. Tufescu, K. Reid, S. Raptis, B.G. Campling, and L. Raptis. 1998. A functional assay for intercellular, junctional communication in cultured human lung carcinoma cells. Lab. Investig. 78:639-640.

Brownell, H.L., S. Giorgetti-Peraldi, E. Tomai, K.L. Firth, and L. Raptis. 1998. In situ electroporation in the study of signal transduction, G.G. Skouteris and G.L. Nickolson (eds.), Intermolecular cross-talk in tumor metastasis. IOS Press, Netherlands.

Brownell, H.L., K.L. Firth, K. Kawauchi, T.L. Delovitch, and L. Raptis. 1997. A novel technique for the study of Ras activation; electroporation of [a32P]GTP. DNA Cell Biol. 16:103-110.

Raptis, L., J. Yang, H.L. Brownell, J. Lai, T. Preston, M.J. Corbley, R.P. Narsimhan, and T. Haliotis. 1997. Rasleu61 blocks differentiation of transformable 3T3 L1 and C3H10T1/2-derived preadipocytes in a dose- and time-dependent manner. Cell Growth. Differ. 8:11-21.

Preston, T., H.L. Brownell, and L. Raptis. 1997. The timing of insulin/c-Ras signal is critical for its effect upon the differentiation of 10T1/2-derived preadipocytes. Cancer Lett. 115:165-171.

Raptis, L., H.L. Brownell, K. Wood, M. Corbley, D. Wang, and T. Haliotis. 1997. Cellular ras gene activity is required for full neoplastic transformation by Simian Virus 40. Cell Growth Differ. 8:891-901.

Brownell, H.L., J.F. Whitfield, and L. Raptis. 1997. Elimination of intercellular junctional communication requires lower Rasleu61 levels than stimulation of anchorage-independent proliferation. Cancer Detect. Prev. 21:289-294.

Firth, K.L., H.L. Brownell, and L. Raptis. 1997. An improved procedure for electroporation of peptides into adherent cells in situ. Biotechniques, 23:644-645.

Raptis, L., H.L. Brownell, Y. Lu, T. Preston, R.P. Narsimhan, E. Schaefer, S. Anderson, and T. Haliotis. 1997. v-Ras and v-Raf block differentiation of transformable C3H10T1/2-derived preadipocytes at lower levels than required for neoplastic transformation. Exp. Cell Res., 235:188-197.

Brownell, H.L., Narsimhan, R.P., Corbley, M.J., Mann, V.M., Whitfield, J.J. and Raptis, L. 1996. Ras is involved in gap junction closure in fibroblasts or preadipocytes but not differentiated adipocytes. DNA Cell Biol. 15:443-451.

Brownell, H.L., J.F. Whitfield, and Raptis, L. 1996. Cellular Ras partly mediates gap junction closure by the polyoma virus middle Tumor antigen. Cancer Letters, 103:99-106.

Royal, I., L. Raptis, B.J. Druker, and N. Marceau. 1996. Down- regulation of cytokeratin 14 gene expression by the polyoma virus middle-T antigen is dependent on c-src association but independent of full transformation in rat liver nonparenchymal epithelial cells. Cell Growth Differ. 7:737-743.