May regulate STK11/LKB1 function by controlling its subcellular localization. Found in a ternary complex composed of STK11/LKB1, STK11IP and SMAD4 (By similarity). Interacts with SMAD4 (By similarity). Interacts with STK11/LKB1. Some cells show granular or punctuate expression. Colocalizes with STK11/LKB1 and SMAD4 in granular or punctuate structures (By similarity). Belongs to the STK11IP family.