(662a) Activation of IRE1? Protein By Palmitate through the Transmembrane Domain and Its Implications in Progression of Cancer

An increase in free fatty acid levels and endoplasmic reticulum (ER) stress are observed in various cancers (e.g. hepatocellular carcinoma) and altered fatty acid metabolism is required to sustain tumor cells. Saturated free fatty acids (FFAs) are known inducers of ER stress. We have found previously that palmitate (PA) led to the migration and invasion of liver cancer cells, and expressed markers for epithelial-to-mesenchymal transition (EMT). However, the mechanism by which PA induces ER stress to promote EMT is unclear.

ER stress is sensed through IRE1, PERK and ATF6 sensor proteins. These transmembrane proteins are involved in maintaining ER homeostasis and failure to correct ER stress is implicated in the pathology of many diseases. Several researchers including our group have found that saturated FFAs activate IRE1α, a transmembrane (TM) serine-threonine protein kinase/endoribonuclease.

IRE1α is activated through dimerization of its luminal domain. We recently uncovered that PA, unlike other ER stressors such as tunicamycin, DTT and thapsigargin, activates IRE1α through a non-canonical luminal-domain independent mechanism. Using a bimolecular fluorescence (BiFC) assay we confirmed that PA induces the dimerization of the TM-IRE1α leading to activation and identified two important residues S450 and W457 that form a part of the dimer interface on IRE1α and are important for dimerization and activation of the protein.

In addition to metabolism, we found that PA increased the invasiveness and metastatic ability of livers cells mediated by the ER stress sensor protein, IRE1α. Therefore, we developed IRE1α ^-/^- hepatocellular carcinoma cell lines using CRISPR editing to study the changes in metabolism mediated by PA-induced IRE1α activation that contribute to cancer progression and aggressiveness.