Rho/ROCK pathway inhibition by the CDK inhibitor p27kip1 participates in the onset of macrophage 3D-mesenchymal migration

Abstract

Infiltration of macrophages into tissue can promote tumour development. Depending on the extracellular matrix architecture, macrophages can adopt two migration modes: amoeboid migration - common to all leukocytes, and mesenchymal migration - restricted to macrophages and certain tumour cells. Here, we investigate the initiating mechanisms involved in macrophage mesenchymal migration. We show that a single macrophage is able to use both migration modes. Macrophage mesenchymal migration is correlated with decreased activity of Rho/Rho-associated protein kinase (ROCK) and is potentiated when ROCK is inhibited, suggesting that amoeboid inhibition participates in mechanisms that initiate mesenchymal migration. We identify the cyclindependent kinase (CDK) inhibitor p27kip1 (also known as CDKN1B) as a new effector of macrophage 3D-migration. By using p27kip1 mutant mice and small interfering RNA targeting p27kip1, we show that p27kip1 promotes mesenchymal migration and hinders amoeboid migration upstream of the Rho/ROCK pathway, a process associated with a relocation of the protein from the nucleus to the cytoplasm. Finally, we observe that cytoplasmic p27kip1 is required for in vivo infiltration of macrophages within induced tumours in mice. This study provides the first evidence that silencing of amoeboid migration through inhibition of the Rho/ROCK pathway by p27kip1 participates in the onset of macrophage mesenchymal migration.