LyGDI functions in cancer metastasis by anchoring Rho proteins to the cell membrane

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Abstract
Rho family GTPases play an important role in a number of processes related to metastasis, and RhoGDP dissociation, inhibitors (RhoGDIs) regulate Rho family proteins. We cloned genomic DNA from colon carcinoma SW480 cells capable of transforming nonmetastatic ras‐transformed 1‐1ras1000 cells into metastatic cells. This DNA contained a truncated human ras homolog gene family GDP dissociation inhibitor beta (ARHGDIB) gene, resulting in a C‐terminal truncated form of LyGDI (ΔC‐LyGDI, 166–201 deletion), a member of the RhoGDIs. The stable expression of ΔC‐LyGDI induced pulmonary metastasis in 1‐1ras1000 cells, whereas expression of full‐length LyGDI did not induce metastasis. ΔC‐LyGDI was preferentially localized in the membrane, detected in a NP‐40‐insoluble fraction, and co‐purified with radixin, moesin, Rac1, Cdc42, and RhoA. In ΔC‐LyGDI transfectant, an activation state of Rac1 was elevated and ΔC‐LyGDI was associated with Rac1‐GTP. In keeping with the observed localization of Rac1 to the cell membrane and the elevated level of Rac1‐GTP, ΔC‐LyGDI transfectants were found to be more invasive than mock transfectant. These results suggest that LyGDI functions in the cell membrane to afford spatial regulation of Rho family GTPase signaling through ezrin radixin moesin (ERM) proteins during metastasis.