CLP-36 PDZ-LIM protein associates with nonmuscle alpha-actinin-1 and alpha-actinin-4

The PDZ-LIM family of proteins (Enigma/LMP-1, ENH, ZASP/Cypher, RIL, ALP, a nd CLP-36) has been suggested to act as adapters that direct LIM-binding pr oteins to the cytoskeleton, Most interactions of PDZ-LIM proteins with the cytoskeleton have been identified in striated muscle, where several PDZ-LIM proteins are predominantly expressed. By contrast, CLP-36 mRNA is expresse d in several nonmuscle tissues, and here we demonstrate high expression of CLP-36 in epithelial cells by in situ hybridization analysis. Our subcellul ar localization studies indicate that in nonmuscle cells, CLP-36 protein lo calizes to actin stress fibers. This localization is mediated via the PDZ d omain of CLP-36 that associates with the spectrin-like repeats of alpha-act inin. Interestingly, immunoprecipitation and matrix-assisted laser desorpti on/ionization time-of-flight mass spectrometry analysis indicate that both nonmuscle alpha-actinin-1 and alpha-actinin-4 form complexes with CLP-36, T he high expression of alpha-actinin-4 in the colon, together with these res ults, suggests a specific function for the alpha-actinin-4-CLP-36 complex i n the colonic epithelium, More generally, results presented here demonstrat e that the association of PDZ-LIM proteins with the cytoskeleton extends to the actin stress fibers of nonmuscle cells.