Rho GTPase Involvement in Breast Cancer Migration and Invasion

The RhoGTPases play a critical role in cell migration via regulation of cytoskeletal changes. Increased expression of Rho proteins. in particular RhoC, have been associated with invasive carcinoma, however, the functional contributions of the individual isoforms have been difficult to evaluate due to insufficient molecular tools. We used a stable retroviral RNAi approach to abrogate expression of RhoA or RhoC in the SUM-159 invasive breast carcinoma cell line. We observed that loss of RhoA stimulates invasion, resulting in enhanced lammellipodia formation and decreased adhesion to laminin-I. Conversely, loss of RhoC diminishes invasive potential and impedes cell spreading and lammellipodia formation. A compensatory relationship between RhoA and RhoC at the level of expression and activation was observed and we postulate the reduction in invasive potential for the RhoC siRNA cells results from loss of RhoC expression, as well as increased RhoA activity. Increased invasion in the RhoA siRNA cells results from decreased RhoA and increased RhoC activity but other factors may also contribute based on the use of C3 transferase to inactivate all Rho isoforms. Preliminary in vivo orthotopic studies reveal that RhoC is important for tumour formation while RhoA may regulate the angiogenic response via regulation of VEGF protein expression.