Rac1 and Rac3 isoform activation is involved in the invasive and metastatic phenotype of human breast cancer cells.
BACKGROUND
The metastatic progression of cancer is a direct result of the disregulation of numerous cellular signaling pathways, including those associated with adhesion, migration, and invasion. Members of the Rac family of small GTPases are known to act as regulators of actin cytoskeletal structures and strongly influence the cellular processes of integrin-mediated adhesion and migration. Even though hyperactivated Rac proteins have been shown to influence metastatic processes, these proteins have never been directly linked to metastatic progression.


METHODS
To investigate a role for Rac and Cdc42 in metastatic breast cancer cell invasion and migration, relative endogenous Rac or Cdc42 activity was determined in a panel of metastatic variants of the MDA-MB-435 metastatic human breast cancer cell line using a p21-binding domain-PAK pull down assay. To investigate the migratory and invasive potential of the Rac isoforms in human breast cancer, namely Rac1 and the subsequently cloned Rac3, we stably expressed either dominant active Rac1 or dominant active Rac3 into the least metastatic cell variant. Dominant negative Rac1 or dominant negative Rac3 were stably expressed in the most metastatic cell variant. Cell lines expressing mutant Rac1 or Rac3 were analyzed using in vitro adhesion, migration and invasion assays.


RESULTS
We show that increased activation of Rac proteins directly correlates with increasing metastatic potential in a panel of cell variants derived from a single metastatic breast cancer cell line (MDA-MB-435). The same correlation could not be found with activated Cdc42. Expression of a dominant active Rac1 or a dominant active Rac3 resulted in a more invasive and motile phenotype. Moreover, expression of either dominant negative Rac1 or dominant negative Rac3 into the most metastatic cell variant resulted in decreased invasive and motile properties.


CONCLUSIONS
This study correlates endogenous Rac activity with high metastatic potential and implicates Rac in the regulation of cell migration and invasion in metastatic breast cancer cells. Taken together, these results suggest a role for both the Rac1 and Rac3 GTPases in human breast cancer progression.
Baugher
Paige J
PJ
Molecular Cell and Developmental Biology Section and The Institute for Cellular and Molecular Biology, The University of Texas at Austin, University Station, Austin, TX 78712, USA. p.baugher@mail.utexas.edu
Krishnamoorthy
Lakshmi
L
Price
Janet E
JE
Dharmawardhane
Surangani F
SF
D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D002465:Cell Movement; D004789:Enzyme Activation; D005260:Female; D020869:Gene Expression Profiling; D006801:Humans; D009361:Neoplasm Invasiveness; D009362:Neoplasm Metastasis / Q000235:genetics*; D010641:Phenotype; D014407:Tumor Cells, Cultured; D020764:cdc42 GTP-Binding Protein / Q000096:biosynthesis / Q000378:metabolism; D020744:rac GTP-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*
C107953:RAC1 protein, human; C411563:RAC3 protein, human; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein