Ciliary transport regulates PDGF-AA/αα signaling via elevated mammalian target of rapamycin signaling and diminished PP2A activity.
Primary cilia are built and maintained by intraflagellar transport (IFT), whereby the two IFT complexes, IFTA and IFTB, carry cargo via kinesin and dynein motors for anterograde and retrograde transport, respectively. Many signaling pathways, including platelet- derived growth factor (PDGF)-AA/αα, are linked to primary cilia. Active PDGF-AA/αα signaling results in phosphorylation of Akt at two residues: P-Akt(T308) and P-Akt(S473), and previous work showed decreased P-Akt(S473) in response to PDGF-AA upon anterograde transport disruption. In this study, we investigated PDGF-AA/αα signaling via P-Akt(T308) and P-Akt(S473) in distinct ciliary transport mutants. We found increased Akt phosphorylation in the absence of PDGF-AA stimulation, which we show is due to impaired dephosphorylation resulting from diminished PP2A activity toward P-Akt(T308). Anterograde transport mutants display low platelet-derived growth factor receptor (PDGFR)α levels, whereas retrograde mutants exhibit normal PDGFRα levels. Despite this, neither shows an increase in P-Akt(S473) or P-Akt(T308) upon PDGF-AA stimulation. Because mammalian target of rapamycin complex 1 (mTORC1) signaling is increased in ciliary transport mutant cells and mTOR signaling inhibits PDGFRα levels, we demonstrate that inhibition of mTORC1 rescues PDGFRα levels as well as PDGF-AA-dependent phosphorylation of Akt(S473) and Akt(T308) in ciliary transport mutant MEFs. Taken together, our data indicate that the regulation of mTORC1 signaling and PP2A activity by ciliary transport plays key roles in PDGF-AA/αα signaling.
Genetics and Molecular Biology Graduate Programs, Emory University School of Medicine, Atlanta, GA 30322 Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322.
Nicole L
NL
Umberger
Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322.
Tamara
T
Caspary
D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000235:genetics; D015153:Blotting, Western; D002478:Cells, Cultured; D002923:Cilia / Q000378:metabolism*; D004622:Embryo, Mammalian / Q000166:cytology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D000076222:Mechanistic Target of Rapamycin Complex 1; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D046912:Multiprotein Complexes / Q000378:metabolism; D009154:Mutation; D010766:Phosphorylation / Q000187:drug effects; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D054648:Protein Phosphatase 2 / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D020796:Receptor, Platelet-Derived Growth Factor alpha / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
D046912:Multiprotein Complexes; D010982:Platelet-Derived Growth Factor; C075278:platelet-derived growth factor A; C546843:mTOR protein, mouse; D020796:Receptor, Platelet-Derived Growth Factor alpha; D000076222:Mechanistic Target of Rapamycin Complex 1; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D054648:Protein Phosphatase 2; D020123:Sirolimus