Cyclopamine inhibition of Sonic hedgehog signal transduction is not mediated through effects on cholesterol transport.
Cyclopamine is a teratogenic steroidal alkaloid that causes cyclopia by blocking Sonic hedgehog (Shh) signal transduction. We have tested whether this activity of cyclopamine is related to disruption of cellular cholesterol transport and putative secondary effects on the Shh receptor, Patched (Ptc). First, we report that the potent antagonism of Shh signaling by cyclopamine is not a general property of steroidal alkaloids with similar structure. The structural features of steroidal alkaloids previously associated with the induction of holoprosencephaly in whole animals are also associated with inhibition of Shh signaling in vitro. Second, by comparing the effects of cyclopamine on Shh signaling with those of compounds known to block cholesterol transport, we show that the action of cyclopamine cannot be explained by inhibition of intracellular cholesterol transport. However, compounds that block cholesterol transport by affecting the vesicular trafficking of the Niemann-Pick C1 protein (NPC1), which is structurally similar to Ptc, are weak Shh antagonists. Rather than supporting a direct link between cholesterol homeostasis and Shh signaling, our findings suggest that the functions of both NPC1 and Ptc involve a common vesicular transport pathway. Consistent with this model, we find that Ptc and NPC1 colocalize extensively in a vesicular compartment in cotransfected cells.
Department of Biological Structure, University of Washington, Seattle 98195, USA.
J P
JP
Incardona
W
W
Gaffield
Y
Y
Lange
A
A
Cooney
P G
PG
Pentchev
S
S
Liu
J A
JA
Watson
R P
RP
Kapur
H
H
Roelink
D000736:Androstenes / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D019556:COS Cells; D002352:Carrier Proteins; D002642:Chick Embryo; D002784:Cholesterol / Q000378:metabolism*; D053823:Hedgehog Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D000077296:Niemann-Pick C1 Protein; D015513:Oncogene Proteins / Q000378:metabolism; D011374:Progesterone / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D015534:Trans-Activators; D014162:Transfection; D014704:Veratrum Alkaloids / Q000494:pharmacology*
D000736:Androstenes; D002352:Carrier Proteins; D053823:Hedgehog Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; C106881:NPC1 protein, human; D000077296:Niemann-Pick C1 Protein; D015513:Oncogene Proteins; D011506:Proteins; D011994:Recombinant Proteins; C509239:SHH protein, human; D015534:Trans-Activators; D014704:Veratrum Alkaloids; C006261:3-beta-(2-(diethylamino)ethoxy)androst-5-en-17-one; D011374:Progesterone; D002784:Cholesterol; C000541:cyclopamine