Neutral endopeptidase inhibits neuropeptide-mediated transactivation of the insulin-like growth factor receptor-Akt cell survival pathway.
G-protein coupled receptor (GPCR) agonists such as neuropeptides activate the insulin-like growth factor-1 receptor (IGF-IR) or the serine-threonine protein kinase Akt, suggesting that neuropeptides-GPCR signaling can cross-communicate with IGF-IR-Akt signaling pathways. Neutral endopeptidase 24.11 (NEP) is a cell-surface peptidase that cleaves and inactivates the neuropeptides endothelin-1 (ET-1) and bombesin, which are implicated in progression to androgen-independent prostate cancer (PC). We investigated the mechanisms of NEP regulation of neuropeptide-mediated cell survival in PC cells, including whether neuropeptide substrates of NEP induce phosphorylations of IGF-IR and Akt in PC cells. Western analyses revealed ET-1 and bombesin treatment induced phosphorylation of IGF-IRbeta and Akt independent of IGF-I in TSU-Pr1, DU145, and PC-3 PC cells, which lack NEP expression, but not in NEP-expressing LNCaP cells. Recombinant NEP and induced NEP expression in TSU-Pr1 cells using a tetracycline-repressive expression system inhibited ET-1-mediated phosphorylation of IGF-IRbeta and Akt, and blocked the protective effects of ET-1 against apoptosis induced by serum starvation. Incubation of TSU-Pr1 cells with specific kinase inhibitors together with ET-1 or bombesin showed that IGF-IR activation is required for neuropeptide-induced Akt phosphorylation, and that neuropeptide-induced Akt activation is predominantly mediated by Src and phosphatidylinositol 3-kinase but not by mitogen-activated protein kinase or protein kinase C. These data show that the neuropeptides ET-1 and bombesin stimulate ligand-independent activation of the IGF-IR, which results in Akt activation, and that this cross-communication between GPCR and IGF-IR signaling is inhibited by NEP.
Sumitomo
M
M
Urologic Oncology Research Laboratory, Department of Urology, Weill Medical College of Cornell University, New York, NY 10021, USA.
Milowsky
M I
MI
Shen
R
R
Navarro
D
D
Dai
J
J
Asano
T
T
Hayakawa
M
M
Nanus
D M
DM
D001839:Bombesin / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D002470:Cell Survival / Q000502:physiology; D019332:Endothelin-1 / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D004789:Enzyme Activation; D006801:Humans; D008297:Male; D015260:Neprilysin / Q000502:physiology*; D010766:Phosphorylation; D011471:Prostatic Neoplasms / Q000201:enzymology / Q000473:pathology; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D017526:Receptor, IGF Type 1 / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D019061:src-Family Kinases / Q000378:metabolism
D019332:Endothelin-1; D011518:Proto-Oncogene Proteins; D017526:Receptor, IGF Type 1; D019061:src-Family Kinases; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D015260:Neprilysin; D001839:Bombesin