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