The ras oncogene is involved in the formation of a significant portion of human tumors. Ras, the protein encoded by ras, is a small guanine nucleotide-binding protein which inappropriately signals cell growth in its oncogenically activated form. Unpublished studies using pharmacological inhibitors of cellular Ras activity (farnesyl transferase inhibitors, or FTIs) have revealed that a Rho family protein, RhoB, may be necessary for malignant cell transformation by oncogenic ras. Rho proteins are part of the Ras superfamily of guanine nucleotide-binding proteins and have been implicated in regulation of specific actin cytoskeletal structures. Some Rho proteins have been speculated to be involved in Ras-induced signaling and/or cytoskeletal changes, but this question has not been directly tested; RhoB itself is biologically uncharacterized and its molecular effector functions are unexplored. An identification of the activities and effector molecules controlled by RhoB signaling is important because of (1) the potential therapeutic importance of these functions and (2) their likelihood of providing basic insights into our understanding of cytoskeleton-based signal transduction. Significantly, FTIs cause reversion of cells transformed by oncogenic Ras but have little effect on the growth of normal cells, despite their requirement for normal Ras activity. Because we have determined that a critical event in FTI-induced reversion of ras- transformed cells process is inhibition of Rhob, the results suggest that malignant cell growth may preferentially require a RhoB-dependent function(s) which may be largely dispensible in normal cells. Underlying the clinical relevance of this issue is the more fundamental question of how cytoskeletal actin structures may function in signal transduction, the current understanding of which is heavily weighed toward the study of diffusible signaling agents. It would therefore be important to identify the molecular effector molecules and downstream signaling targets of RhoB, in order to begin to dissect pathways that could be mechanistically novel as well as well as therapeutically useful. We propose to address these issues in a test of the hypothesis that RhoB- regulated processes are critical for Ras-dependent signal transduction and malignant cell transformation. Briefly, we aim to: genetically inhibit cellular RhoB activity to establish that it is necessary for initiating and maintaining ras-dependent cell transformation; identify ras- and/or growth factor-activated """"""""immediate-early"""""""" genes and regulatory elements which are controlled by RhoB signaling activity; clone RhoB effector molecule(s); genetically inhibit candidate effector molecules in normal or ras- transformed cells to establish that their activity is necessary for normal or transformed cell growth

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
First Independent Research Support & Transition (FIRST) Awards (R29)
Project #
5R29CA065892-05
Application #
2837688
Study Section
Cellular Biology and Physiology Subcommittee 1 (CBY)
Program Officer
Mohla, Suresh
Project Start
1994-12-09
Project End
1999-05-03
Budget Start
1998-12-01
Budget End
1999-05-03
Support Year
5
Fiscal Year
1999
Total Cost
Indirect Cost
Name
Wistar Institute
Department
Type
DUNS #
042250712
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
Liu, A x; Du, W; Liu, J P et al. (2000) RhoB alteration is necessary for apoptotic and antineoplastic responses to farnesyltransferase inhibitors. Mol Cell Biol 20:6105-13
Du, W; Lebowitz, P F; Prendergast, G C (1999) Elevation of alpha2(I) collagen, a suppressor of Ras transformation, is required for stable phenotypic reversion by farnesyltransferase inhibitors. Cancer Res 59:2059-63
Du, W; Liu, A; Prendergast, G C (1999) Activation of the PI3'K-AKT pathway masks the proapoptotic effects of farnesyltransferase inhibitors. Cancer Res 59:4208-12
Du, W; Lebowitz, P F; Prendergast, G C (1999) Cell growth inhibition by farnesyltransferase inhibitors is mediated by gain of geranylgeranylated RhoB. Mol Cell Biol 19:1831-40
Du, W; Prendergast, G C (1999) Geranylgeranylated RhoB mediates suppression of human tumor cell growth by farnesyltransferase inhibitors. Cancer Res 59:5492-6
Basu, A; Rodeck, U; Prendergast, G C et al. (1999) Loss of insulin-like growth factor I receptor-dependent expression of p107 and cyclin A in cells that lack the extracellular matrix protein secreted protein acidic and rich in cysteine. Cell Growth Differ 10:721-8
Lebowitz, P F; Prendergast, G C (1998) Functional interaction between RhoB and the transcription factor DB1. Cell Adhes Commun 6:277-87
Lebowitz, P F; Casey, P J; Prendergast, G C et al. (1997) Farnesyltransferase inhibitors alter the prenylation and growth-stimulating function of RhoB. J Biol Chem 272:15591-4
Lebowitz, P F; Du, W; Prendergast, G C (1997) Prenylation of RhoB is required for its cell transforming function but not its ability to activate serum response element-dependent transcription. J Biol Chem 272:16093-5
Lebowitz, P F; Sakamuro, D; Prendergast, G C (1997) Farnesyl transferase inhibitors induce apoptosis of Ras-transformed cells denied substratum attachment. Cancer Res 57:708-13

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