title: Leptin potentiates antiproliferative action of cAMP elevation via protein kinase A down-regulation in breast cancer cells.
abstract: Previously, we have shown that leptin potentiates the antiproliferative action of cAMP elevating agents in breast cancer cells and that the protein kinase A (PKA) inhibitor KT-5720 prevented the antiproliferative effects induced by the leptin plus cAMP elevation. The present experiments were designed to gain a better understanding about the PKA role in the antitumor interaction between leptin and cAMP elevating agents and on the underlying signaling pathways. Here we show that exposure of MDA-MB-231 breast cancer cells to leptin resulted in a strong phosphorylation of both ERK1/2 and STAT3. Interestingly, intracellular cAMP elevation upon forskolin pretreatment completely abrogated both ERK1/2 and STAT3 phosphorylation in response to leptin and was accompanied by a consistent CREB phosphorylation. Notably, leptin plus forskolin cotreatments resulted in a strong decrease of both PKA regulatory RIα and catalytic subunits protein levels. Importantly, pretreatment with the PKA inhibitor KT-5720 blocked the forskolin-induced CREB phosphorylation and prevented both the inhibition by forskolin of leptin-induced ERK1/2 and STAT3 phosphorylation and the PKA subunits down-regulation induced by the combination of leptin and forskolin. Altogether, our results indicate that leptin-dependent signaling pathways are influenced by cAMP elevation and identify PKA as relevantly involved in the pharmacological antitumor interaction between leptin and cAMP elevating drugs in MDA-MB-231 cells. We propose a molecular model by which PKA confers its effects. Potential therapeutic applications by our data will be discussed.
authors.affiliation: Department of Biochemistry and Biophysics, Second University of Naples, Medical School, Naples, Italy. silvio.naviglio@unina2.it
authors.forename: Silvio
authors.initials: S
authors.lastname: Naviglio
authors.forename: Davide
authors.initials: D
authors.lastname: Di Gesto
authors.forename: Fausto
authors.initials: F
authors.lastname: Illiano
authors.forename: Emilio
authors.initials: E
authors.lastname: Chiosi
authors.forename: Antonio
authors.initials: A
authors.lastname: Giordano
authors.forename: Gennaro
authors.initials: G
authors.lastname: Illiano
authors.forename: Annamaria
authors.initials: A
authors.lastname: Spina
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D001943:Breast Neoplasms / Q000201:enzymology* / Q000473:pathology; D002227:Carbazoles / Q000494:pharmacology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D054751:Cyclic AMP-Dependent Protein Kinase Catalytic Subunits / Q000378:metabolism; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015536:Down-Regulation; D020536:Enzyme Activators / Q000494:pharmacology; D005260:Female; D006801:Humans; D020738:Leptin / Q000378:metabolism*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D011994:Recombinant Proteins / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D015854:Up-Regulation
chemical_list: D000970:Antineoplastic Agents; C115163:CREB1 protein, human; D002227:Carbazoles; D017362:Cyclic AMP Response Element-Binding Protein; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; D020536:Enzyme Activators; D020738:Leptin; D047428:Protein Kinase Inhibitors; D011758:Pyrroles; D011994:Recombinant Proteins; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D005576:Colforsin; C057416:KT 5720; D000242:Cyclic AMP; D054751:Cyclic AMP-Dependent Protein Kinase Catalytic Subunits; D017868:Cyclic AMP-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3