Inhibitors of clathrin-dependent endocytosis enhance TGFβ signaling and responses

Clathrin-dependent endocytosis is believed to be involved in TGF beta-stimulated cellular responses, but the subcellular locus at which TGF beta induces signaling remains unclear. Here, we demonstrate that inhibitors of clathrin-dependent endocytosis, which are known to arrest the progression of endocytosis at coated-pit stages, inhibit internalization of cell-surface-bound TGF beta and promote colocalization and accumulation of T beta R-I and SARA at the plasma membrane. These inhibitors enhance TGF beta-induced signaling and cellular responses (Smad2 phosphorylation/nuclear localization and expression of PAI-1). Dynasore, a newly identified inhibitor of dynamin GTPase activity, is one of the most potent inhibitors among those tested and, furthermore, is a potent enhancer of TGF beta. Dynasore ameliorates atherosclerosis in the aortic endothelium of hypercholesterolemic ApoE-null mice by counteracting the suppressed TGF beta responsiveness caused by the hypercholesterolemia, presumably acting through its effect on TGF beta endocytosis and signaling in vascular cells.