Oxysterols are allosteric activators of the oncoprotein Smoothened

Abstract

Oxysterols are a class of endogenous signaling molecules that can activate the Hedgehog pathway, which plays critical roles in development, regeneration and cancer. However, it has been unclear how oxysterols influence Hedgehog signaling, including whether their effects are mediated through a protein target or indirectly through effects on membrane properties. To answer this question, we synthesized the enantiomer and an epimer of the most potent oxysterol, 20(S)-hydroxycholesterol. Using these molecules, we show that the effects of oxysterols on Hedgehog signaling are exquisitely stereoselective, consistent with their function through a specific protein target. We present several lines of evidence that this protein target is the 7-pass transmembrane protein Smoothened, a major drug target in oncology. Our work suggests that these enigmatic sterols, which have multiple effects on cell physiology, may act as ligands for signaling receptors and provides a generally applicable framework for probing their mechanism of action.

Endogenous B-ring oxysterols inhibit the Hedgehog component Smoothened in a manner distinct from cyclopamine or side-chain oxysterols

“…Curiously, despite its inhibition of 20(S)-OHC activation, DHCEO does not completely block the synergy between 20(S)-OHC and SAG (39). We thus found that addition of 20(S)-OHC both increased the potency of SAG (reduced its EC 50 ) and increased the maximum level of pathway activation achieved (Fig.…”

“…5A). DHCEO also inhibited two other CRD agonists, 7-keto-27-hydroxycholesterol (7KCh-27OH) (18) and 20(S)-yne (39), in an apparently noncompetitive manner (Fig. 5 B and C).…”

Psychosine, the cytotoxic sphingolipid that accumulates in globoid cell leukodystrophy, alters membrane architecture

“…lipid. Psy and its enantiomer altered bilayers of liposomes, making them more water permeable and allowing the vesicles to expand their volume as the added sphingolipid partitioned into the membrane ( 21,36 ). It is clear that psy and ent-psy alter the integrity of model membrane systems.…”

Lipoproteins carry endocannabinoids that inhibit the Hedgehog pathway

“…Hydroxysterols have been shown to stimulate Smo activity [9,10,11] by binding to its Nterminal domain [11,12,13]. Although MS/MS analysis detected hydroxysterols in fractions 33-peer-reviewed) is the author/funder.…”