Interaction of Two Actin-binding Proteins, Synaptopodin and α-Actinin-4, with the Tight Junction Protein MAGI-1

• Published in: The Journal of biological chemistry 2002-08, Vol.277 (33), p.30183
• Main Authors: Kevin M. Patrie, Andrew J. Drescher, Ajith Welihinda, Peter Mundel, Ben Margolis
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M203072200

In an attempt to find podocyte-expressed proteins that may interact with the tight junction protein MAGI-1, we screened a glomerulus-enriched cDNA library with a probe consisting of both WW domains of MAGI-1. One of the isolated clones contained two WW domain-binding motifs and was identified as a portion of the actin-bundling protein synaptopodin. In vitro binding assays confirmed this interaction between MAGI-1 and synaptopodin and identified the second WW domain of MAGI-1 to be responsible for the interaction. MAGI-1 and synaptopodin can also interact in vivo , as they can be immunoprecipitated together from HEK293 cell lysates. Another actin-bundling protein that is found in glomerular podocytes and shown to be mutated in an inheritable form of glomerulosclerosis is α-actinin-4. We show that α-actinin-4 is also capable of binding to MAGI-1 in in vitro binding assays and that this interaction is mediated by the fifth PDZ domain of MAGI-1 binding to the C terminus of α-actinin-4. Exogenously expressed synaptopodin and α-actinin-4 were found to colocalize along with endogenous MAGI-1 at the tight junction of Madin-Darby canine kidney cells. The interaction and colocalization of MAGI-1 with two actin-bundling proteins suggest that MAGI-1 may play a role in actin cytoskeleton dynamics within polarized epithelial cells.