An interaction between LKB1 and IPMK is necessary for metformin-mediated AMPK activation. A, 293T cells were cotransfected with GST or GST-IPMK and Myc-LKB1 for 30 hours, followed by GST pull-down and immunoblotting for Myc-LKB1. B, Cells were cotransfected with plasmids encoding various N-terminal truncated fragments (1–433, 97–433, 197–433, or 377–433 amino acids) and either GST or a GST-IPMK in HEK293T cells for 48 hours, followed by pull-down and immunoblotting for Myc-LKB1 fragments.