DBeQ

DBeQ blocks UbG76V-GFP, ODD-Luc and Luc-ODC degradation with IC50 of 2.6 μM, 56 μM and 45 μM in HeLa cells. DBeQ is at least 50-fold less potent toward N-ethylmaleimide–sensitive factor (NSF) and 26S proteasome. DBeQ inhibits p97 competitively with respect to ATP, with Ki of 3.2 μM, suggesting that it binds to the active site of the D2 domain. DBeQ (10 μM) potently blocks degradation of TCRα-GFP in HEK293 cells. DBeQ induces CHOP within 3 hours in a concentration-dependent manner but does not increase p21 level in HEK293 cells. DBeQ (15 μM) induces a strong accumulation of LC3-II in the nucleus plus membrane-enriched and cytosolic fractions in Hela cells. DBeQ acts by blocking autophagic degradation of LC3-II instead of inducing autophagy in HeLa cells. DBeQ (10 μM) rapidly promotes activation of the “executioner” caspases-3 and -7 in HeLa cells. DBeQ activates the intrinsic caspase-9 apoptotic pathway more than the extrinsic caspase-8 pathway, whereas STS activates both pathways to a similar extent. DBeQ is fivefold more active against multiple myeloma (RPMI8226) cells than normal human fetal lung fibroblasts (MRC5), with HeLa and Hek293 cells showing intermediate sensitivities. ^[1] DBeQ exhibits 20-fold selectivity for stabilizing p97-dependent vs. independent UPS reporter substrates in HeLa cells. DBeQ impairs degradation of substrates within the ERAD and autophagy pathways. ^[2] DBeQ (12 μM) inhibits intracellular neutralization in a dose-dependent manner in HeLa cells. DBeQ (10 μM), which completely inhibits degradation of virus and antibody in the fate-of-capsid experiment, fails to prevent degradation of IgG Fc. DBeQ (9 μM) reduces the initial gradient of neutralization as a function of antibody concentration. ^[3] DBeQ decreases both basal and nutrient-stimulated phosphorylation of MTOR targets similar to the effects of rapamycin in U20S cells. ^[4]