Cellular Cholesterol Directly Activates Smoothened in Hedgehog Signaling

Huang, Peiying; Nedelcu, Daniel; Watanabe, Mayu; Jao, Cindy Y.; Kim, Young Chang; Liu, Jing; Salic, Adrian

doi:10.1016/j.cell.2016.08.003

Cited by 308 publications

(346 citation statements)

References 43 publications

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“…Thus, the instructive effects of cholesterol revealed in our present study and the permissive effects of cholesterol reported previously map to distinct, separable SMO domains. Our observation that MβCD:cholesterol is sufficient to activate SMO through its CRD is in agreement with a report published recently during the review process of our manuscript (Huang et al, 2016). …”

Section: Discussionsupporting

confidence: 94%

Cholesterol activates the G-protein coupled receptor Smoothened to promote Hedgehog signaling

Luchetti

Sircar

Kong

et al. 2016

eLife

197

211

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Cholesterol is necessary for the function of many G-protein coupled receptors (GPCRs). We find that cholesterol is not just necessary but also sufficient to activate signaling by the Hedgehog (Hh) pathway, a prominent cell-cell communication system in development. Cholesterol influences Hh signaling by directly activating Smoothened (SMO), an orphan GPCR that transmits the Hh signal across the membrane in all animals. Unlike many GPCRs, which are regulated by cholesterol through their heptahelical transmembrane domains, SMO is activated by cholesterol through its extracellular cysteine-rich domain (CRD). Residues shown to mediate cholesterol binding to the CRD in a recent structural analysis also dictate SMO activation, both in response to cholesterol and to native Hh ligands. Our results show that cholesterol can initiate signaling from the cell surface by engaging the extracellular domain of a GPCR and suggest that SMO activity may be regulated by local changes in cholesterol abundance or accessibility.DOI: http://dx.doi.org/10.7554/eLife.20304.001

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Section: Discussionsupporting

confidence: 94%

Cholesterol activates the G-protein coupled receptor Smoothened to promote Hedgehog signaling

Luchetti

Sircar

Kong

et al. 2016

eLife

197

211

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“…S1A) (26). In the crystal structure of SMO CRD, Tyr103 forms a hydrogen bond with the hydroxyl group of 20 (S)-hydroxycholesterol (27). Remarkably, the ligand bound in the hydrophobic groove of SMO at the same position where the free fatty acid could bind in hFZD7 CRD (SI Appendix, Fig.…”

Section: Resultsmentioning

confidence: 99%

Unsaturated fatty acyl recognition by Frizzled receptors mediates dimerization upon Wnt ligand binding

Nile¹,

Mukund²,

Stanger³

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

105

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Frizzled (FZD) receptors mediate Wnt signaling in diverse processes ranging from bone growth to stem cell activity. Moreover, high FZD receptor expression at the cell surface contributes to overactive Wnt signaling in subsets of pancreatic, ovarian, gastric, and colorectal tumors. Despite the progress in biochemical understanding of Wnt-FZD receptor interactions, the molecular basis for recognition of Wnt cis-unsaturated fatty acyl groups by the cysteine-rich domain (CRD) of FZD receptors remains elusive. Here, we determined a crystal structure of human FZD7 CRD unexpectedly bound to a 24-carbon fatty acid. We also report a crystal structure of human FZD5 CRD bound to C16:1 cis-Δ9 unsaturated fatty acid. Both structures reveal a dimeric arrangement of the CRD. The lipid-binding groove exhibits flexibility and spans both monomers, adopting a U-shaped geometry that accommodates the fatty acid. Re-evaluation of the published mouse FZD8 CRD structure reveals that it also shares the same architecture as FZD5 and FZD7 CRDs. Our results define a common molecular mechanism for recognition of the cis-unsaturated fatty acyl group, a necessary posttranslational modification of Wnts, by multiple FZD receptors. The fatty acid bridges two CRD monomers, implying that Wnt binding mediates FZD receptor dimerization. Our data uncover possibilities for the arrangement of Wnt-FZD CRD complexes and shed structural insights that could aide in the identification of pharmacological strategies to modulate FZD receptor function.nt signaling is evolutionarily conserved from metazoans to humans (1). It is critical for tissue homeostasis and during development (2, 3). On the other hand, derangements in Wnt signaling are associated with severe pathologies in mammals, including cancer (4-6). Signaling is initiated at the cell surface where the secreted, lipid-modified Wnt glycoprotein interacts with the extracellular N-terminal cysteine-rich domain (CRD) of the frizzled (FZD) receptor (7). This high-affinity interaction occurs at two distinct contact sites, one comprising a protein-fatty acyl interface and another a protein-protein interaction interface (8-10). Sequence analysis revealed that there are 10 human frizzled genes grouped into four clusters (SI Appendix, Fig. S1A).Among their multiple roles in physiology, FZD receptors have emerged as critical regulators of Wnt-dependent stem cell processes. For example, FZD7 is a critical component of the stem cell niche and was shown by genetic knockdown experiments to be essential for maintaining human embryonic and epithelial limbal stem cells in an undifferentiated state (11,12). Of the 10 mammalian frizzleds, FZDs 1, 2, and 7 are enriched at the base of mammalian adult intestinal crypts where the stem cells reside (13,14), and FZD7 is required for stem cell-mediated regeneration of the intestinal epithelium (15). Moreover, high FZD receptor expression at the cell surface contributes to overactive Wnt signaling in subsets of pancreatic, ovarian, gastric, and colorectal tumors (16)(17)(18)(19)...

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“…Additionally, the high affinity HDL receptor SCARB1 was reported to be over expressed in a wide range of malignancies, including breast cancer 45 , pancreatic cancer 46 , renal cell carcinoma 47 , chronic lymphocytic leukemia 48 , and prostate cancer 9 , and has been identified as an independent prognostic factor associated with worse outcomes in breast cancer. 45 The HDL NPs are a unique cholesterol depletion agent that, due to their composition, specifically target SCARB1 17–19, 48, 49 , making them an ideal component of a cholesterol depleting therapeutic regimen.…”

Section: Discussionmentioning

confidence: 99%

Rational Targeting of Cellular Cholesterol in Diffuse Large B-Cell Lymphoma (DLBCL) Enabled by Functional Lipoprotein Nanoparticles: A Therapeutic Strategy Dependent on Cell of Origin

et al. 2017

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Cancer cells have altered metabolism and, in some cases, an increased demand for cholesterol. It is important to identify novel, rational treatments based on biology, and cellular cholesterol metabolism as a potential target for cancer is an innovative approach. Toward this end, we focused on diffuse large B-cell lymphoma (DLBCL) as a model because there is differential cholesterol biosynthesis driven by B-cell receptor (BCR) signaling in germinal center (GC) versus activated B-cell (ABC) DLBCL. To specifically target cellular cholesterol homeostasis, we employed high-density lipoprotein-like nanoparticles (HDL NP) that can generally reduce cellular cholesterol by targeting and blocking cholesterol uptake through the high-affinity HDL receptor, scavenger receptor type B-1 (SCARB1). As we previously reported, GC DLBCL are exquisitely sensitive to HDL NP as monotherapy while ABC DLBCL are less sensitive. Herein, we report that enhanced BCR signaling and resultant de novo cholesterol synthesis in ABC DLBCL drastically reduces the ability of HDL NPs to reduce cellular cholesterol and induce cell death. Therefore, we combined HDL NP with the BCR signaling inhibitor ibrutinib and the SYK inhibitor R406. By targeting both cellular cholesterol uptake and BCR-associated de novo cholesterol synthesis, we achieved cellular cholesterol reduction and induced apoptosis in otherwise resistant ABC DLBCL cell lines. These results in lymphoma demonstrate that reduction of cellular cholesterol is a powerful mechanism to induce apoptosis. Cells rich in cholesterol require HDL NP therapy to reduce uptake and molecularly targeted agents that inhibit upstream pathways that stimulate de novo cholesterol synthesis, thus, providing a new paradigm for rationally targeting cholesterol metabolism as therapy for cancer.

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Cellular Cholesterol Directly Activates Smoothened in Hedgehog Signaling

Cited by 308 publications

References 43 publications

Cholesterol activates the G-protein coupled receptor Smoothened to promote Hedgehog signaling

Cholesterol activates the G-protein coupled receptor Smoothened to promote Hedgehog signaling

Unsaturated fatty acyl recognition by Frizzled receptors mediates dimerization upon Wnt ligand binding

Rational Targeting of Cellular Cholesterol in Diffuse Large B-Cell Lymphoma (DLBCL) Enabled by Functional Lipoprotein Nanoparticles: A Therapeutic Strategy Dependent on Cell of Origin

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