title: Syk inhibits the activity of protein kinase A by phosphorylating tyrosine 330 of the catalytic subunit.
abstract: The Syk protein-tyrosine kinase can have multiple effects on cancer cells, acting in some as a tumor suppressor by inhibiting motility and in others as a tumor promoter by enhancing survival. Phosphoproteomic analyses identified PKA as a Syk-specific substrate. Syk catalyzes the phosphorylation of the catalytic subunit of PKA (PKAc) both in vitro and in cells on Tyr-330. Tyr-330 lies within the adenosine-binding motif in the C-terminal tail of PKAc within a cluster of acidic amino acids (DDYEEEE), which is a characteristic of Syk substrates. The phosphorylation of PKAc on Tyr-330 by Syk strongly inhibits its catalytic activity. Molecular dynamics simulations suggest that this additional negative charge prevents the C-terminal tail from interacting with the substrate and the nucleotide-binding site to stabilize the closed conformation of PKAc, thus preventing catalysis from occurring. Phosphoproteomic analyses and Western blotting studies indicate that Tyr-330 can be phosphorylated in a Syk-dependent manner in MCF7 breast cancer cells and DT40 B cells. The phosphorylation of a downstream substrate of PKAc, cAMP-responsive element-binding protein (CREB), is inhibited in cells expressing Syk but can be rescued by a selective inhibitor of Syk. Modulation of CREB activity alters the expression of the CREB-regulated gene BCL2 and modulates cellular responses to genotoxic agents. Thus, PKA is a novel substrate of Syk, and its phosphorylation on Tyr-330 inhibits its participation in downstream signaling pathways.
authors: Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana 47907, USA.
authors: Shuai
authors: S
authors: Yu
authors: He
authors: H
authors: Huang
authors: Anton
authors: A
authors: Iliuk
authors: Wen-Horng
authors: WH
authors: Wang
authors: Keerthi B
authors: KB
authors: Jayasundera
authors: W Andy
authors: WA
authors: Tao
authors: Carol B
authors: CB
authors: Post
authors: Robert L
authors: RL
authors: Geahlen
mesh_terms: D020816:Amino Acid Motifs; D050882:CREB-Binding Protein / Q000235:genetics / Q000378:metabolism; D020134:Catalytic Domain / Q000502:physiology; D045744:Cell Line, Tumor; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D004249:DNA Damage / Q000502:physiology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D008297:Male; D010766:Phosphorylation / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D000072377:Syk Kinase; D014443:Tyrosine
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D014443:Tyrosine; D050882:CREB-Binding Protein; C494363:CREBBP protein, human; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D017868:Cyclic AMP-Dependent Protein Kinases