A Novel Small-Molecule GRP94 Modulator Increases PCSK9 Secretion and Promotes LDLR Degradation.

The endoplasmic reticulum (ER) maintains protein homeostasis through chaperone-mediated folding and ER-associated degradation (ERAD). Disruption of this quality control, particularly involving the ER chaperone GRP94, contributes to diseases such as hypercholesterolemia, cancer, and immune disorders, where defective GRP94-dependent folding and the trafficking of client proteins like PCSK9, integrins, and Toll-like receptors drive pathology. Here, we characterize NSC637153 (cp153), a small molecule identified in a drGFP-based ERAD dislocation screen, as a selective probe of GRP94-dependent processes. cp153 inhibits the dislocation of ERAD substrates, preferentially affecting luminal clients, increases PCSK9 secretion, and promotes LDLR degradation. Unlike ATP-competitive HSP90 inhibitors, cp153 does not induce HSP70 or destabilize AKT, suggesting that it perturbs GRP94 function by interfering with client interaction or folding. The identification of cp153 provides a useful tool to for probing GRP94's role in protein folding, trafficking, ER quality control, and disease-relevant signaling pathways, and supports the development of client-selective GRP94-targeted therapies.