TM4SF5-mediated Resistance against EGFR Kinase Inhibitors Involves an IGF1R Cooperation.

Abstract

Transmembrane 4 L6 family member 5 (TM4SF5) is a membrane protein similar to the tetraspanins highly expressed in Hepatocellular carcinoma (HCC), and causes enhanced migration and invasion. TM4SF5 collaborates with other membrane proteins during its pro-tumorigenic roles, presumably at tetraspanin-enriched microdomain (TEM). Here, we explored the TM4SF5-mediated resistance against the clinically important EGFR kinase inhibitors, with regards to a cooperation with another membrane protein especially Insulin-like growth factor 1 receptor (IGF1R). In this study, therefore, I explored resistance against anti-tumor drugs using non-small cell lung carcinoma (NSCLC) cell lines that are ectopically overexpressing TM4SF5 or have suppressed IGF1R levels. When the NSCLC cells were tested with diverse anti-cancer drugs, TM4SF5-positive and/or IGF1R-positive cell lines showed more resistance against EGFR kinase inhibitors (TKIs), Erlotinib or Gefitinib, but not PDGFR/Raf kinase inhibitor, sorafenib. The levels of TM4SF5 and IGF1R modulated each other. Meanwhile, either suppression in EGFR TKI-resistant NCI-H1299 cells caused sensitizations to the EGFR kinase inhibitors, whereas expression of either of TM4SF5 and IGF1R caused activation of its downstream signaling molecules like ERKs, AKT, and S6K leading to resistance against the TKIs. Furthermore, TM4SF5 and IGF1R formed a complex each other, and even further, the complex included EGFR. The complex of EGFR, IGF1R, and TM4SF5 would be sustained in EGFR TKIs treated conditions. In addition to these 2 dimensional (2D) condition, the cells were examined for the drug resistancy when they were embedded in 3D collagen I gels. TM4SF5 and/or IGF1R expression in HCC827 and NCI-H1299 cell lines gave them compact spheroid formation ability in a less-adhesive aquaoues cell culture system. Further, the spheroids with high expression of TM4SF5 and IGF1R were resistant against EGFR TKIs, gefitinib and erlotinib. Thus, this study evidences that TM4SF5 and/or IGF1R appeared to collaborate to cause survival signaling, forming with a triple complex with EGFR, even with EGFR TK.