Filamin A (FLNA) plays an essential role in somatostatin receptor 2 (SST2) signaling and stabilization after agonist stimulation in human and rat somatotroph tumor cells.
Somatostatin receptor type 2 (SST2) is the main pharmacological target of medical therapy for GH-secreting pituitary tumors, but molecular mechanisms regulating its expression and signaling are largely unknown. The aim of this study was to investigate the role of cytoskeleton protein filamin A (FLNA) in SST2 expression and signaling in somatotroph tumor cells. We found a highly variable expression of FLNA in human GH-secreting tumors, without a correlation with SST2 levels. FLNA silencing in human tumoral cells did not affect SST2 expression and localization but abolished the SST2-induced reduction of cyclin D1 (-37% ± 15% in control cells, P < .05 vs basal) and caspase-3/7 activation (+63% ± 31% in control cells, P < .05 vs basal). Overexpression of a FLNA dominant-negative mutant that specifically prevents SST2-FLNA binding reduced SST2 expression after prolonged agonist exposure (-55% ± 5%, P < .01 vs untreated cells) in GH3 cells. Moreover, SST2-induced apoptotic effect (77% ± 54% increase of caspase activity, P < .05 vs basal) and SST2-mediated ERK1/2 inhibition (48% ± 17% reduction of ERK1/2 phosphorylation, P < .01 vs basal) were abrogated in cells overexpressing another FLNA mutant that prevents FLNA interaction with partner proteins but not with SST2, suggesting a scaffold function of FLNA in somatotrophs. In conclusion, these data demonstrate that FLNA is involved in SST2 stabilization and signaling in tumoral somatotrophs, playing both a structural and functional role.
Endocrine Unit (E.P., E.G., D.T., A.S., G.M.), Department of Clinical Sciences and Community Health, Neurosurgery Unit (M.L.), Fondazione Istituto di Ricovero e Cura a Carattere Scientifico Ca' Granda Ospedale Maggiore Policlinico, 20122, Milano, Italy; Laboratory of Cellular and Molecular Endocrinology (E.V., V.C.), Humanitas Research Center, Neurosurgery Unit (G.B.L.), and Endocrine Unit (A.G.L.), IRCCS Clinical and Research Institute Humanitas, Rozzano, University of Milan, 20089 Milan, Italy.
E
E
Peverelli
E
E
Giardino
D
D
Treppiedi
E
E
Vitali
V
V
Cambiaghi
M
M
Locatelli
G B
GB
Lasio
A
A
Spada
A G
AG
Lania
G
G
Mantovani
D000818:Animals; D017209:Apoptosis; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D064448:Filamins / Q000502:physiology*; D006801:Humans; D055550:Protein Stability; D051381:Rats; D017481:Receptors, Somatostatin / Q000819:agonists / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D052683:Somatotrophs / Q000378:metabolism*
D064448:Filamins; D017481:Receptors, Somatostatin; C093733:somatostatin receptor 2