PRAS40 activates the IRE1α-XBP-1-mediated unfolded protein response to exacerbate colorectal cancer by enhancing ST6Gal1-dependent α-2, 6 sialylation of GRP78

Colorectal cancer (CRC) progression could be fueled by the activation of the unfolded protein response (UPR) triggered by endoplasmic reticulum (ER) stress. The proline-rich Akt1 substrate of 40 kDa (PRAS40) is implicated in cancer progression, but its role in the UPR remains unclear. Herein, we demonstrate that PRAS40 promotes the inositol-requiring enzyme 1α (IRE1α)-X-box binding protein 1 (XBP1) axis-dependent UPR in driving CRC progression. Mechanistically, PRAS40 interacts with ER chaperone glucose-regulated protein 78 (GRP78) and enhances its N-glycosylation. Moreover, PRAS40 improves the interaction between GRP78 and ST6 β-galactoside α-2, 6-sialyltransferase 1 (ST6Gal1), leading to increased α-2, 6-sialylation of GRP78 and the UPR triggered by ER stress. Furthermore, we identified the natural compound β-sitosterol as a novel ST6Gal1 inhibitor, which attenuated PRAS40-triggered tumor growth. Collectively, these findings unveil a PRAS40-ST6Gal1-GRP78 axis that drives CRC progression through activating the IRE1α-XBP-1-mediated UPR and nominate ST6Gal1 as a promising therapeutic target.