title: Filamin-A is essential for dopamine d2 receptor expression and signaling in tumorous lactotrophs.
abstract: BACKGROUND
  Dopamine agonists (DA) are the first choice treatment of prolactinomas. However, a subset of patients is resistant to DA, due to undefined dopamine D2 receptor (D2R) alterations. Recently, D2R was found to associate with filamin-A (FLNA), a widely expressed cytoskeleton protein with scaffolding properties, in melanoma and neuronal cells.
  
  
  OBJECTIVE
  The aim of the study was to investigate the role of FLNA in D2R expression and signaling in human tumorous lactotrophs and rat MMQ and GH3 cells.
  
  
  METHODS
  We analyzed FLNA expression in a series of prolactinomas by immunohistochemistry and Western blotting. We performed FLNA silencing or transfection experiments in cultured cells from DA-sensitive or -resistant prolactinomas and in MMQ and GH3 cells, followed by analysis of D2R expression and signaling.
  
  
  RESULTS
  We demonstrated reduced FLNA and D2R expression in DA-resistant tumors. The crucial role of FLNA on D2R was demonstrated by experiments showing that: 1) FLNA silencing in DA-sensitive prolactinomas resulted in 60% reduction of D2R expression and abrogation of DA-induced inhibition of prolactin release and antiproliferative signals, these results being replicated in MMQ cells that endogenously express FLNA and D2R; and 2) FLNA overexpression in DA-resistant prolactinomas restored D2R expression and prolactin responsiveness to DA, whereas this manipulation was ineffective in GH3 cells that express FLNA but not D2R. No alteration in FLNA promoter methylation was detected, ruling out the occurrence of epigenetic FLNA silencing in DA-resistant prolactinomas.
  
  
  CONCLUSIONS
  These data indicate that FLNA is crucial for D2R expression and signaling in lactotrophs, suggesting that the impaired response to DA may be related to the reduction of FLNA expression in DA-resistant prolactinomas.
authors.affiliation: Endocrinology Unit, Department of Medical Sciences, Fondazione Instituto di Ricovero e Cura a Carattere Scientifico Ca' Granda-Padiglione Granelli, University of Milan, Via Francesco Sforza, 35, 20122 Milan, Italy.
authors.forename: Erika
authors.initials: E
authors.lastname: Peverelli
authors.forename: Giovanna
authors.initials: G
authors.lastname: Mantovani
authors.forename: Eleonora
authors.initials: E
authors.lastname: Vitali
authors.forename: Francesca M
authors.initials: FM
authors.lastname: Elli
authors.forename: Luca
authors.initials: L
authors.lastname: Olgiati
authors.forename: Stefano
authors.initials: S
authors.lastname: Ferrero
authors.forename: Edward R
authors.initials: ER
authors.lastname: Laws
authors.forename: Pamela
authors.initials: P
authors.lastname: Della Mina
authors.forename: Antonello
authors.initials: A
authors.lastname: Villa
authors.forename: Paolo
authors.initials: P
authors.lastname: Beck-Peccoz
authors.forename: Anna
authors.initials: A
authors.lastname: Spada
authors.forename: Andrea G
authors.initials: AG
authors.lastname: Lania
mesh_terms: D000818:Animals; D049109:Cell Proliferation; D003285:Contractile Proteins / Q000235:genetics / Q000378:metabolism*; D064448:Filamins; D006801:Humans; D052682:Lactotrophs / Q000378:metabolism*; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D010911:Pituitary Neoplasms / Q000235:genetics / Q000378:metabolism*; D015175:Prolactinoma / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017448:Receptors, Dopamine D2 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D014407:Tumor Cells, Cultured
chemical_list: D003285:Contractile Proteins; D064448:Filamins; D008840:Microfilament Proteins; D017448:Receptors, Dopamine D2