Apparent receptor-mediated activation of Ca2+-dependent conductive Cl- transport by shark-derived polyaminosterols.
The shark liver antimicrobial polyaminosterol squalamine is an angiogenesis inhibitor under clinical investigation as an anti-cancer agent and as a treatment for the choroidal neovascularization associated with macular degeneration of the retina. The related polyaminosterol MSI-1436 is an appetite suppressant that decreases systemic insulin resistance. However, the mechanisms of action of these polyaminosterols are unknown. We report effects of MSI-1436 on Xenopus oocytes consistent with the existence of a receptor for polyaminosterols. MSI-1436 activates bidirectional, trans-chloride-independent Cl- flux in Xenopus oocytes. At least part of this DIDS-sensitive Cl- flux is conductive, as measured using two-electrode voltage-clamp and on-cell patch-clamp techniques. MSI-1436 also elevates cytosolic Ca2+ concentration ([Ca2+]) and increases bidirectional 45Ca2+ flux. Activation of Cl- flux and elevation of cytosolic [Ca2+] by MSI-1436 both are accelerated by lowering bath Ca2+ and are not acutely inhibited by extracellular EGTA. Elevation of cytosolic [Ca2+] by MSI-1436 requires heparin-sensitive intracellular Ca2+ stores. Although injected EGTA abolishes the increased conductive Cl- flux, that Cl- flux is not dependent on heparin-sensitive stores. In low-bath Ca2+ conditions, several structurally related polyaminosterols act as strong agonists or weak agonists of conductive Cl- flux in oocytes. Weak agonist polyaminosterols antagonize the strong agonist, MSI-1436, but upon addition of the conductive Cl- transport inhibitor DIDS, they are converted into strong agonists. Together, these properties operationally define a polyaminosterol receptor at or near the surface of the Xenopus oocyte, provide an initial description of receptor signaling, and suggest routes toward further understanding of a novel class of appetite suppressants and angiogenesis inhibitors.
Chernova
Marina N
MN
Molecular and Vascular Medicine Unit, Beth Israel Deaconess Medical Center, Department of Medicine, Harvard Medical School, Boston, MA 02215, USA.
Vandorpe
David H
DH
Clark
Jeffrey S
JS
Williams
Jon I
JI
Zasloff
Michael A
MA
Jiang
Lianwei
L
Alper
Seth L
SL
D000818:Animals; D001685:Biological Factors / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D018118:Chloride Channels / Q000187:drug effects / Q000502:physiology*; D002713:Chlorine / Q000378:metabolism*; D002777:Cholestanols; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008099:Liver / Q000737:chemistry; D009865:Oocytes / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D012754:Sharks / Q000378:metabolism*; D013261:Sterols / Q000494:pharmacology*; D014982:Xenopus laevis
D001685:Biological Factors; D018118:Chloride Channels; D002777:Cholestanols; D011956:Receptors, Cell Surface; D013261:Sterols; D002713:Chlorine; C079655:squalamine; D002118:Calcium