title: Increased IGFBP-1 phosphorylation in response to leucine deprivation is mediated by CK2 and PKC.
abstract: Insulin-like growth factor binding protein-1 (IGFBP-1), secreted by fetal liver, is a key regulator of IGF-I bioavailability and fetal growth. IGFBP-1 phosphorylation decreases IGF-I bioavailability and diminishes its growth-promoting effects. Growth-restricted fetuses have decreased levels of circulating essential amino acids. We recently showed that IGFBP-1 hyperphosphorylation (pSer101/119/169) in response to leucine deprivation is regulated via activation of the amino acid response (AAR) in HepG2 cells. Here we investigated nutrient-sensitive protein kinases CK2/PKC/PKA in mediating IGFBP-1 phosphorylation in leucine deprivation. We demonstrated that leucine deprivation stimulated CK2 activity (enzymatic assay) and induced IGFBP-1 phosphorylation (immunoblotting/MRM-MS). Inhibition (pharmacological/siRNA) of CK2/PKC, but not PKA, prevented IGFBP-1 hyperphosphorylation in leucine deprivation. PKC inhibition also prevented leucine deprivation-stimulated CK2 activity. Functionally, leucine deprivation decreased IGF-I-induced-IGF-1R autophosphorylation when CK2/PKC were not inhibited. Our data strongly support that PKC promotes leucine deprivation-induced IGFBP-1 hyperphosphorylation via CK2 activation, mechanistically linking decreased amino acid availability and reduced fetal growth.
authors.affiliation: Dept of Biochemistry, University of Western Ontario, London, Ontario N6A 5C1, Canada.
authors.forename: Niyati
authors.initials: N
authors.lastname: Malkani
authors.affiliation: Dept of Biochemistry, University of Western Ontario, London, Ontario N6A 5C1, Canada.
authors.forename: Kyle
authors.initials: K
authors.lastname: Biggar
authors.affiliation: Children's Health Research Institute, University of Western Ontario, London, ON, Canada.
authors.forename: Majida Abu
authors.initials: MA
authors.lastname: Shehab
authors.affiliation: Dept of Biochemistry, University of Western Ontario, London, Ontario N6A 5C1, Canada.
authors.forename: Shawn Shun-Cheng
authors.initials: SS
authors.lastname: Li
authors.affiliation: Dept of Obstetrics & Gynecology, University of Colorado Anschutz Medical Campus, Aurora, CO, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Jansson
authors.affiliation: Dept of Biochemistry, University of Western Ontario, London, Ontario N6A 5C1, Canada; Children's Health Research Institute, University of Western Ontario, London, ON, Canada; Dept of Pediatrics, University of Western Ontario, London, Canada. Electronic address: mbgupta@uwo.ca.
authors.forename: Madhulika B
authors.initials: MB
authors.lastname: Gupta
mesh_terms: D047390:Casein Kinase II / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D005786:Gene Expression Regulation; D056945:Hep G2 Cells; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000378:metabolism*; D007930:Leucine / Q000172:deficiency*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*
chemical_list: C032231:IGFBP1 protein, human; D018970:Insulin-Like Growth Factor Binding Protein 1; D047390:Casein Kinase II; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D007930:Leucine
keywords: Amino acid restriction; Fetal growth; HepG2 cells; Insulin-like growth Factor-1 receptor; Insulin-like growth factor binding protein; Mass spectrometry; Phosphorylation sites; Protein kinases