Analysis of Rac Mutations in Breast Cancer

Institution: Scripps Research Institute
Investigator(s): Janis Jackson, M.D. -
Award Cycle: 1997 (Cycle III) Grant #: 3IB-0073 Award: $87,413
Award Type: IDEA
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease



Initial Award Abstract (1997)
The cellular changes involved in the transformation of normal cells to cancerous cells includes a category of regulatory proteins involved in a process termed signal transduction. These signaling proteins can ultimately determine the synthesis of specific genes necessary for tumor cell behavior, cell division, or other metabolic changes in cancer cells. These cancer-promoting proteins/genes are often referred to as oncogenes. They alter cell behavior when they are expressed inappropriately or become mutated. Recent studies have shown that the Rac 1 oncogene, a member of the Ras superfamily of proteins, may play an important role in carcinogenesis and/or metastasis. First, Rac 1 has been shown to (i) be required for Ras-induced malignant transformation, (ii) induce cell cycle progression and DNA synthesis in Swiss 3T3 fibroblasts, and (iii) transform normal cells into malignant cells. Second, Rac 1 protein is known to regulate an activity of phagocytes (NADPH oxidase) that is believed to contribute to the pathogenesis of many human tumors. Third, Rac 1 (in conjunction with Rho and/or CDC42) controls the assembly of polymerized actin structures (cytoskeleton) and associated cell surface adhesion complexes; and it is thought that these abilities enable Rac 1 to play a key role in regulating tumor cell motility, adhesion, and metastasis.

We hypothesized that Rac 1 might be mutated in human breast cancers, and be responsible for certain aspects of its pathogenesis. To initially test our hypothesis, we isolated RNA from metastatic, infiltrating ductal human breast carcinomas, and directly sequenced it (through PCR-amplified DNA) to detect the presence of Rac 1 mutations. Our preliminary results showed a mutation in codon #12 in 4 of the 5 breast carcinoma tissues. To our knowledge, this is the first demonstration of mutated Rac 1 in human cancers.

The overall goal of this IDEA research project is to confirm and expand on these findings to determine if Rac 1 is mutated in human breast carcinomas. If Rac 1 is found to be frequently mutated and activated in human breast cancers, it may provide a novel target in the development of anti-breast cancer therapeutics.


Final Report (1998)
Rac 1 is a member of the Ras Superfamily of GTP-binding proteins. Rac 1 regulates the activity of the superoxide anion-generating NADPH oxidase system of phagocytes, plays a central role in organization of the actin cytoskeleton, and is essential for Ras-induced transformation. In addition, mutant, constitutively active, Rac 1 can induce cellular transformation, invasion, and metastasis. Human cells contain 3 homologous Rac proteins: Rac 1, 2 and 3, that are essentially identical except for their hypervariable C-terminal domains. Rac 1, but not Rac 2 or 3, contains a polybasic domain within its hypervariable region that is virtually identical to the polybasic domain of K-Ras 4B. Rac 1 is a member of the Ras Superfamily of GTP-binding proteins. Rac 1 regulates the activity of the superoxide anion-generating NADPH oxidase system of phagocytes, plays a central role in organization of the actin cytoskeleton, and is essential for Ras-induced transformation. In addition, mutant, constitutively active, Rac 1 can induce cellular transformation, invasion, and metastasis. Similar to Ras proteins, Rac 1 is activated by upstream GEFs, and binds effector proteins that signal downstream. Human cells contain 3 homologous Rac proteins: Rac 1, 2 and 3, that are essentially identical except for their hypervariable C-terminal domains. Rac 1, but not Rac 2 or 3, contains a polybasic domain within its hypervariable region that is virtually identical to the polybasic domain of K-Ras 4B.

Using a PCR (Polymerase Chain Reaction) approach we have analyzed breast cancer tissues from 37 patients, and we have found mutations in the Rac 1 gene in 17 of these samples. All of the mutations occur in a single exon. In the future, we plan to analyze additional breast cancer tissues, in order to establish the exact frequency of Rac 1 mutations in breast cancers, and study how this Rac 1 mutation might be involved in disease progression. Thus, with BCRP support we were able to confirm our hypothesis that Rac 1 is mutated in a significant number of breast cancers.

Four human ras homologs differ in their abilities to activate Raf-1, induce transformation, and stimulate cell motility
Periodical:Journal of Biological Chemistry
Index Medicus: J Biol Chem
Authors: Voice JK, Klemke RL, Le A, Jackson JH
Yr: 1999 Vol: 274 Nbr: Abs: Pg:17164-17170