title: Characterization of the intracellular mechanisms mediating somatostatin and lanreotide inhibition of DNA synthesis and growth hormone release from dispersed human GH-secreting pituitary adenoma cells in vitro.
abstract: OBJECTIVE
  Somatostatin is an endogenous inhibitor of hormone secretion and cell proliferation. Treatment with somatostatin analogues in humans causes a reduction in size and secretory activity of endocrine tumours, including GH-secreting pituitary adenomas. This study was aimed to characterize the intracellular mechanisms mediating the in vitro antiproliferative and antisecretory effects of somatostatin and its analogue lanreotide, on primary cultures of GH-secreting pituitary adenoma cells.
  
  
  METHODS
  Thirteen GH-secreting pituitary adenoma postsurgical specimens were analysed for somatostatin receptor (SSTR) mRNA expression and a subset of them was analysed in vitro for the effect of somatostatin on cell proliferation, assessed by means of [3H]-thymidine uptake, and GH release, using an immunoradiometric assay. Moreover, the intracellular signalling involved in such effects has been studied.
  
  
  RESULTS
  All the adenomas analysed expressed at least one somatostatin receptor subtype mRNA. SSTR2 mRNA was identified in 77% of the adenomas, SSTR1 and SSTR3 in 69% and SSTR5 in 60%. Somatostatin and lanreotide inhibited cell proliferation in phorbol ester (PMA)-stimulated conditions (10/13 adenomas), as well as after fetal calf serum (3/3 adenomas) or IGF-I stimulation (2/2 adenomas). Conversely, GHRH or forskolin treatments did not significantly affect DNA synthesis in adenoma cells in the presence or absence of somatostatin (2/2 and 4/4 adenomas, respectively). Vanadate pretreatment reversed somatostatin inhibition of PMA-induced DNA synthesis suggesting an involvement of tyrosine phosphatase in this effect (2/2 adenomas); this was confirmed by the direct induction of tyrosine phosphatase activity in two adenomas after somatostatin treatment. Somatostatin and also lanreotide caused significant inhibition of phorbol ester, forskolin, GHRH and KCl-dependent increase of GH secretion in the culture medium. Moreover, voltage-sensitive calcium channel activity induced by 40 mm KCl depolarization in microfluorimetric analysis, was significantly reduced (5/5 adenomas).
  
  
  CONCLUSIONS
  These data show that somatostatin and lanreotide inhibit human GH-secreting pituitary adenoma cell proliferation and hormone release in vitro, and suggest that the activation of tyrosine phosphatases may represent intracellular signals mediating the antiproliferative effects and that the inhibition of the voltage-dependent calcium channels and adenylyl cyclase activities may control GH secretion.
authors.affiliation: Pharmacology and Neuroscience, National Institute for Cancer Research, c/o Advanced Biotechnology Center (CBA), Genova, Italy. florio@cba.unige.it
authors.forename: Tullio
authors.initials: T
authors.lastname: Florio
authors.forename: Stefano
authors.initials: S
authors.lastname: Thellung
authors.forename: Alessandro
authors.initials: A
authors.lastname: Corsaro
authors.forename: Liliana
authors.initials: L
authors.lastname: Bocca
authors.forename: Sara
authors.initials: S
authors.lastname: Arena
authors.forename: Alessandra
authors.initials: A
authors.lastname: Pattarozzi
authors.forename: Valentina
authors.initials: V
authors.lastname: Villa
authors.forename: Alessandro
authors.initials: A
authors.lastname: Massa
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Diana
authors.forename: Daria
authors.initials: D
authors.lastname: Schettini
authors.forename: Federica
authors.initials: F
authors.lastname: Barbieri
authors.forename: Jean Louis
authors.initials: JL
authors.lastname: Ravetti
authors.forename: Renato
authors.initials: R
authors.lastname: Spaziante
authors.forename: Massimo
authors.initials: M
authors.lastname: Giusti
authors.forename: Gennaro
authors.initials: G
authors.lastname: Schettini
mesh_terms: D000236:Adenoma / Q000378:metabolism*; D000262:Adenylyl Cyclases / Q000378:metabolism; D000328:Adult; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D015220:Calcium Channels / Q000378:metabolism; D002455:Cell Division; D005576:Colforsin / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D013006:Growth Hormone / Q000378:metabolism* / Q000494:pharmacology; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010456:Peptides, Cyclic / Q000494:pharmacology*; D010911:Pituitary Neoplasms / Q000378:metabolism*; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D017481:Receptors, Somatostatin / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013004:Somatostatin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D010456:Peptides, Cyclic; D012333:RNA, Messenger; D017481:Receptors, Somatostatin; C060347:lanreotide; D005576:Colforsin; D013004:Somatostatin; D013006:Growth Hormone; D004247:DNA; D013007:Growth Hormone-Releasing Hormone; D017027:Protein Tyrosine Phosphatases; D000262:Adenylyl Cyclases