title: Homotypic gap junctional communication associated with metastasis suppression increases with PKA activity and is unaffected by PI3K inhibition.
abstract: Loss of gap junctional intercellular communication (GJIC) between cancer cells is a common characteristic of malignant transformation. This communication is mediated by connexin proteins that make up the functional units of gap junctions. Connexins are highly regulated at the protein level and phosphorylation events play a key role in their trafficking and degradation. The metastasis suppressor breast cancer metastasis suppressor 1 (BRMS1) upregulates GJIC and decreases phosphoinositide-3-kinase (PI3K) signaling. On the basis of these observations, we set out to determine whether there was a link between PI3K and GJIC in tumorigenic and metastatic cell lines. Treatment of cells with the well-known PI3K inhibitor LY294002, and its structural analogue LY303511, which does not inhibit PI3K, increased homotypic GJIC; however, we found the effect to be independent of PI3K/AKT inhibition. We show in multiple cancer cell lines of varying metastatic capability that GJIC can be restored without enforced expression of a connexin gene. In addition, while levels of connexin 43 remained unchanged, its relocalization from the cytosol to the plasma membrane was observed. Both LY294002 and LY303511 increased the activity of protein kinase A (PKA). Moreover, PKA blockade by the small molecule inhibitor H89 decreased the LY294002/LY303511-mediated increase in GJIC. Collectively, our findings show a connection between PKA activity and GJIC mediated by PI3K-independent mechanisms of LY294002 and LY303511. Manipulation of these signaling pathways could prove useful for antimetastatic therapy.
authors.affiliation: Department of Pathology, University of Alabama at Birmingham, Birmingham, Alabama, USA.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Bodenstine
authors.forename: Kedar S
authors.initials: KS
authors.lastname: Vaidya
authors.forename: Aimen
authors.initials: A
authors.lastname: Ismail
authors.forename: Benjamin H
authors.initials: BH
authors.lastname: Beck
authors.forename: Leah M
authors.initials: LM
authors.lastname: Cook
authors.forename: Anne R
authors.initials: AR
authors.lastname: Diers
authors.forename: Aimee
authors.initials: A
authors.lastname: Landar
authors.forename: Danny R
authors.initials: DR
authors.lastname: Welch
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D002450:Cell Communication; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002867:Chromones / Q000494:pharmacology; D018031:Connexin 43 / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005452:Fluoresceins / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D017629:Gap Junctions / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D007546:Isoquinolines / Q000494:pharmacology; D009025:Morpholines / Q000494:pharmacology; D009362:Neoplasm Metastasis; D009369:Neoplasms / Q000378:metabolism / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013449:Sulfonamides / Q000494:pharmacology; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D002867:Chromones; D018031:Connexin 43; D017868:Cyclic AMP-Dependent Protein Kinases; D004791:Enzyme Inhibitors; D005452:Fluoresceins; D007546:Isoquinolines; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010879:Piperazines; D051057:Proto-Oncogene Proteins c-akt; D013449:Sulfonamides; D000077191:Wortmannin; C093555:LY 303511; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; C007740:fluorexon