Gene expression reprogramming governs cellular processes such as proliferation, differentiation and cell migration through the complex and tightly regulated control of transcriptional cofactors that exist in multiprotein complexes. Here we describe SCAI (suppressor of cancer cell invasion), a novel and highly conserved protein that regulates invasive cell migration through three-dimensional matrices. SCAI acts on the RhoA–Dia1 signal transduction pathway and localizes in the nucleus, where it binds and inhibits the myocardin-related transcription factor MAL by forming a ternary complex with serum response factor (SRF). Genome-wide expression analysis surprisingly reveals that one of the strongest upregulated genes after suppression of SCAI is β1-integrin. Decreased levels of SCAI are tightly correlated with increased invasive cell migration, and SCAI is downregulated in several human tumours. Functional analysis of the β1-integrin gene strongly argues that SCAI is a novel transcriptional cofactor that controls gene expression downstream of Dia1 to dictate changes in cell invasive behaviour.