Ndm, a coiled-coil domain protein that suppresses macropinocytosis and has effects on cell migration

The ampA gene has a role in cell migration in Dictyostelium discoideum. Cells overexpressing AmpA show an increase in cell migration, forming large plaques on bacterial lawns. A second-site suppressor of this ampA-overexpressing phenotype identified a previously uncharacterized gene, ndm, which is described here. The Ndm protein is predicted to contain a coiled-coil BAR-like domain—a domain involved in endocytosis and membrane bending. ndm-knockout and Ndm-monomeric red fluorescent protein–expressing cell lines were used to establish a role for ndm in suppressing endocytosis. An increase in the rate of endocytosis and in the number of endosomes was detected in ndm(−) cells. During migration ndm(−) cells formed numerous endocytic cups instead of the broad lamellipodia structure characteristic of moving cells. A second lamellipodia-based function—cell spreading—was also defective in the ndm(−) cells. The increase in endocytosis and the defect in lamellipodia formation were associated with reduced chemotaxis in ndm(−) cells. Immunofluorescence results and glutathione S-transferase pull-down assays revealed an association of Ndm with coronin and F-actin. The results establish ndm as a gene important in regulating the balance between formation of endocytic cups and lamellipodia structures.