Metformin inhibits androgen-induced IGF-IR up-regulation in prostate cancer cells by disrupting membrane-initiated androgen signaling.
We have previously demonstrated that, in prostate cancer cells, androgens up-regulate IGF-I receptor (IGF-IR) by inducing cAMP-response element-binding protein (CREB) activation and CREB-dependent IGF-IR gene transcription through androgen receptor (AR)-dependent membrane-initiated effects. This IGF-IR up-regulation is not blocked by classical antiandrogens and sensitizes cells to IGF-I-induced biological effects. Metformin exerts complex antitumoral functions in various models and may inhibit CREB activation in hepatocytes. We, therefore, evaluated whether metformin may affect androgen-dependent IGF-IR up-regulation. In the AR(+) LNCaP prostate cancer cells, we found that metformin inhibits androgen-induced CRE activity and IGF-IR gene transcription. CRE activity requires the formation of a CREB-CREB binding protein-CREB regulated transcription coactivator 2 (CRTC2) complex, which follows Ser133-CREB phosphorylation. Metformin inhibited Ser133-CREB phosphorylation and induced nuclear exclusion of CREB cofactor CRTC2, thus dissociating the CREB-CREB binding protein-CRTC2 complex and blocking its transcriptional activity. Similarly to metformin action, CRTC2 silencing inhibited IGF-IR promoter activity. Moreover, metformin blocked membrane-initiated signals of AR to the mammalian target of rapamycin/p70S6Kinase pathway by inhibiting AR phosphorylation and its association with c-Src. AMPK signals were also involved to some extent. By inhibiting androgen-dependent IGF-IR up-regulation, metformin reduced IGF-I-mediated proliferation of LNCaP cells. These results indicate that, in prostate cancer cells, metformin inhibits IGF-I-mediated biological effects by disrupting membrane-initiated AR action responsible for IGF-IR up-regulation and suggest that metformin could represent a useful adjunct to the classical antiandrogen therapy.
Endocrinology (R.M., A.S., A.Morc., A.B.), Department of Health Sciences, University Magna Graecia of Catanzaro, 88100 Catanzaro, Italy; Endocrinology (S.S.), Department of Clinical and Molecular Biomedicine, University of Catania, Garibaldi-Nesima Hospital, 95125 Catania, Italy; Department of General Pathology (A.Mi.), II University of Naples, Via L. De Crecchio, 7-80138 Naples, Italy; Department of Urology and Biology of Prostate Cancer Program (A.Morr.), Kimmel Cancer Center, Thomas Jefferson University, Philadelphia 19107; and Department of Pharmaco-Biology (M.M.), University of Calabria, 87030 Rende, Italy.
Roberta
R
Malaguarnera
Antonella
A
Sacco
Alaide
A
Morcavallo
Sebastiano
S
Squatrito
Antimo
A
Migliaccio
Andrea
A
Morrione
Marcello
M
Maggiolini
Antonino
A
Belfiore
D000728:Androgens / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology; D050882:CREB-Binding Protein / Q000378:metabolism; D002453:Cell Cycle; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects*; D003720:Densitometry; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D008687:Metformin / Q000494:pharmacology*; D009361:Neoplasm Invasiveness; D011471:Prostatic Neoplasms / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D015854:Up-Regulation
D000728:Androgens; D000970:Antineoplastic Agents; C493245:CRTC2 protein, human; D034741:RNA, Small Interfering; D014157:Transcription Factors; D008687:Metformin; D050882:CREB-Binding Protein; C546842:MTOR protein, human; D017526:Receptor, IGF Type 1; D058570:TOR Serine-Threonine Kinases