Serine/Threonine Kinase 11 Interacting Protein (STK11IP)

LIP1 appears to be a cytoplasmically located protein, whereas LKB1 is predominantly nuclear. When LKB1 and LIP1 were coexpressed in vitro, the proportion of cytoplasmic LKB1 dramatically increased, suggesting that LIP1 may regulate LKB1 function by controlling its subcellular localization.

Ectopic expression of both LKB1 and LIP1 in Xenopus embryos induced a secondary body axis, resembling the effects of ectopic expression of TGF-beta superfamily members and their downstream effectors. Furthermore, LIP1 interacted with the TGF-beta-regulated transcription factor SMAD4, forming a LKB1-LIP1-SMAD4 ternary complex. Since SMAD4 mutations give rise to juvenile intestinal polyposis syndrome