1. ¹Department of Pharmacology and Toxicology, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-1031, USA
2. ²Department of Pathology, The University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA
3. ³Department of Experimental Therapeutics, The University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA
4. ⁴Department of Human Biological Chemistry and Genetics, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-1031, USA

Correspondence: X Cheng, E-mail: xcheng@utmb.edu

Received 18 November 2004; Revised 6 April 2005; Accepted 12 April 2005; Published online 6 June 2005.

Abstract

RAS is a small GTP binding protein mutated in approximately 30% human cancer. Despite its important role in the initiation and progression of human cancer, the underlying mechanism of RAS-induced human epithelial transformation remains elusive. In this study, we probe the cellular and molecular mechanisms of RAS-mediated transformation, by profiling two human ovarian epithelial cell lines. One cell line was immortalized with SV40 T/t antigens and the human catalytic subunit of telomerase (T29), while the second cell line was transformed with an additional oncogenic ras^V12 allele (T29H). In total, 32 proteins associated with RAS-mediated transformation have been identified using peptide mass fingerprinting. These protein targets are involved in several cellular pathways, including metabolism, redox balance, calcium signaling, apoptosis, and cellular methylation. One such target, the 40 kDa procaspase 4 is significantly upregulated at the protein level in RAS-transformed T29H cells, related directly to signaling through MEK, but not PI3 kinase. Cellular caspase 4 activity is, however, suppressed in the T29H cells, suggesting that the maturation process of caspase 4 is abrogated in RAS-transformed T29H cells. Consistent with this notion, transformed T29H cells were less susceptible to the toxic effects of anti-Fas antibody than were immortalized, nontransformed T29 cells, associated with less activation of caspase 4. This study demonstrates that functional proteomic analysis of a genetically defined cancer model provides a powerful approach toward systematically identifying cellular targets associated with oncogenic transformation.