title: IGFBP-1 hyperphosphorylation in response to leucine deprivation is mediated by the AAR pathway.
abstract: Insulin-like growth factor-1 (IGF-I) is the key regulator of fetal growth. IGF-I bioavailability is markedly diminished by IGF binding protein-1 (IGFBP-1) phosphorylation. Leucine deprivation strongly induces IGFBP-1 hyperphosphorylation, and plays an important role in fetal growth restriction (FGR). FGR is characterized by decreased amino acid availability, which activates the amino acid response (AAR) and inhibits the mechanistic target of rapamycin (mTOR) pathway. We investigated the role of AAR and mTOR in mediating IGFBP-1 secretion and phosphorylation in HepG2 cells in leucine deprivation. mTOR inhibition (rapamycin or raptor + rictor siRNA), or activation (DEPTOR siRNA) demonstrated a role of mTOR in leucine deprivation-induced IGFBP-1 secretion but not phosphorylation. When the AAR was blocked (U0126, or ERK/GCN2 siRNA), both IGFBP-1 secretion and hyperphosphorylation (pSer101/pSer119/pSer169) due to leucine deprivation were prevented. CK2 inhibition by TBB also attenuated IGFBP-1 phosphorylation in leucine deprivation. These results suggest that the AAR and mTOR independently regulate IGFBP-1 secretion and phosphorylation in response to decreased amino acid availability.
authors.affiliation: Department of Biochemistry, University of Western Ontario, London, Ontario N6A 5C1, Canada.
authors.forename: Niyati
authors.initials: N
authors.lastname: Malkani
authors.affiliation: Department of Obstetrics & Gynecology, University of Colorado, Anschutz Medical Campus, Aurora, Colorado, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Jansson
authors.affiliation: Department of Biochemistry, University of Western Ontario, London, Ontario N6A 5C1, Canada; Department of Pediatrics, University of Western Ontario, London, Canada; Children's Health Research Institute, University of Western Ontario, London, ON, Canada. Electronic address: mbgupta@uwo.ca.
authors.forename: Madhulika B
authors.initials: MB
authors.lastname: Gupta
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D056945:Hep G2 Cells; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000378:metabolism*; D007930:Leucine / Q000172:deficiency; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D000076223:Regulatory-Associated Protein of mTOR; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C032231:IGFBP1 protein, human; D018970:Insulin-Like Growth Factor Binding Protein 1; C492571:RICTOR protein, human; C463659:RPTOR protein, human; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D000076223:Regulatory-Associated Protein of mTOR; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D007930:Leucine; D020123:Sirolimus
keywords: AAR; HepG2 cells; IGFBP-1 phosphorylation; Leucine deprivation; mTOR