Another study found that Cdc42 drives the process of initiating a metastatic tumor in a new tissue by promoting the expression of β1 integrin, an adhesion receptor known to be involved in metastasis. Levels of β1 integrin were reduced in Cdc42-deficient cells. β1 integrin is important for adhesion to the extracellular matrix, and could be important for the initial attachment to endothelial cells as well. Knocking down β1 integrin inhibited cancer cell migration, whereas overexpressing the integrin in Cdc42-deficient cells restored endothelial invasion. Cdc42 promoted β1 integrin expression by activating a transcription factor called SRF. A continually active form of the transcription factor was also capable of restoring endothelial insertion to cancer cells lacking Cdc42.