title: Protein kinase A can block EphA2 receptor-mediated cell repulsion by increasing EphA2 S897 phosphorylation.
abstract: The EphA2 receptor tyrosine kinase plays key roles in tissue homeostasis and disease processes such as cancer, pathological angiogenesis, and inflammation through two distinct signaling mechanisms. EphA2 "canonical" signaling involves ephrin-A ligand binding, tyrosine autophosphorylation, and kinase activity; EphA2 "noncanonical" signaling involves phosphorylation of serine 897 (S897) by AKT and RSK kinases. To identify small molecules counteracting EphA2 canonical signaling, we developed a high-content screening platform measuring inhibition of ephrin-A1-induced PC3 prostate cancer cell retraction. Surprisingly, most hits from a screened collection of pharmacologically active compounds are agents that elevate intracellular cAMP by activating G protein-coupled receptors such as the β2-adrenoceptor. We found that cAMP promotes phosphorylation of S897 by protein kinase A (PKA) as well as increases the phosphorylation of several nearby serine/threonine residues, which constitute a phosphorylation hotspot. Whereas EphA2 canonical and noncanonical signaling have been viewed as mutually exclusive, we show that S897 phosphorylation by PKA can coexist with EphA2 tyrosine phosphorylation and block cell retraction induced by EphA2 kinase activity. Our findings reveal a novel paradigm in EphA2 function involving the interplay of canonical and noncanonical signaling and highlight the ability of the β2-adrenoceptor/cAMP/PKA axis to rewire EphA2 signaling in a subset of cancer cells.
authors.affiliation: Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA 92037.
authors.forename: Antonio
authors.initials: A
authors.lastname: Barquilla
authors.affiliation: Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA 92037.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Lamberto
authors.affiliation: Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA 92037.
authors.forename: Roberta
authors.initials: R
authors.lastname: Noberini
authors.affiliation: Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA 92037.
authors.forename: Susanne
authors.initials: S
authors.lastname: Heynen-Genel
authors.affiliation: Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA 92037.
authors.forename: Laurence M
authors.initials: LM
authors.lastname: Brill
authors.affiliation: Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA 92037 Pathology Department, University of California, San Diego, La Jolla, CA 92093 elenap@sbpdiscovery.org.
authors.forename: Elena B
authors.initials: EB
authors.lastname: Pasquale
mesh_terms: D045744:Cell Line, Tumor; D002465:Cell Movement / Q000502:physiology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D036382:Ephrin-A1 / Q000378:metabolism; D006801:Humans; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D036104:Receptor, EphA2 / Q000378:metabolism*; D011941:Receptors, Adrenergic / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D054852:Small Molecule Libraries
chemical_list: D036382:Ephrin-A1; D011941:Receptors, Adrenergic; D054852:Small Molecule Libraries; D012694:Serine; D000242:Cyclic AMP; D011505:Protein-Tyrosine Kinases; D036104:Receptor, EphA2; D051057:Proto-Oncogene Proteins c-akt; D017868:Cyclic AMP-Dependent Protein Kinases