title: Somatotropinomas, but not nonfunctioning pituitary adenomas, maintain a functional apoptotic RET/Pit1/ARF/p53 pathway that is blocked by excess GDNF.
abstract: Acromegaly is caused by somatotroph cell adenomas (somatotropinomas [ACROs]), which secrete GH. Human and rodent somatotroph cells express the RET receptor. In rodents, when normal somatotrophs are deprived of the RET ligand, GDNF (Glial Cell Derived Neurotrophic Factor), RET is processed intracellularly to induce overexpression of Pit1 [Transcription factor (gene : POUF1) essential for transcription of Pituitary hormones GH, PRL and TSHb], which in turn leads to p19Arf/p53-dependent apoptosis. Our purpose was to ascertain whether human ACROs maintain the RET/Pit1/p14ARF/p53/apoptosis pathway, relative to nonfunctioning pituitary adenomas (NFPAs). Apoptosis in the absence and presence of GDNF was studied in primary cultures of 8 ACROs and 3 NFPAs. Parallel protein extracts were analyzed for expression of RET, Pit1, p19Arf, p53, and phospho-Akt. When GDNF deprived, ACRO cells, but not NFPAs, presented marked level of apoptosis that was prevented in the presence of GDNF. Apoptosis was accompanied by RET processing, Pit1 accumulation, and p14ARF and p53 induction. GDNF prevented all these effects via activation of phospho-AKT. Overexpression of human Pit1 (hPit1) directly induced p19Arf/p53 and apoptosis in a pituitary cell line. Using in silico studies, 2 CCAAT/enhancer binding protein alpha (cEBPα) consensus-binding sites were found to be 100% conserved in mouse, rat, and hPit1 promoters. Deletion of 1 cEBPα site prevented the RET-induced increase in hPit1 promoter expression. TaqMan qRT-PCR (real time RT-PCR) for RET, Pit1, Arf, TP53, GDNF, steroidogenic factor 1, and GH was performed in RNA from whole ACRO and NFPA tumors. ACRO but not NFPA adenomas express RET and Pit1. GDNF expression in the tumors was positively correlated with RET and negatively correlated with p53. In conclusion, ACROs maintain an active RET/Pit1/p14Arf/p53/apoptosis pathway that is inhibited by GDNF. Disruption of GDNF's survival function might constitute a new therapeutic route in acromegaly.
authors.affiliation: Centre for Investigations in Medicine of the USC (E.D.-R., A.R.G.-G., M.G.-L., C.D., C.V.A.), University of Santiago de Compostela, Santiago de Compostela, Spain 15782; Department of Endocrinology (I.B.), University Hospital (University Hospital of Santiago de Compostela), Instituto de Investigación Sanitaria, Santiago de Compostela, Spain 15706; Departments of Cell Biology, Physiology, and Immunology (A.I.-C., E.G.-P., R.M.L., J.P.C.), and Morphological Sciences (L.J.-R.), University of Cordoba, and Reina Sofia University Hospital (P.B., M.A.G.), Maimonides Institute for Research in Biomedicine of Cordoba, Córdoba, Spain 14014; Departments of Endocrinology and Pathology (A.L., M.A.J., A.S., E.V.), Hospital Universitario Virgen del Rocío, Instituto de Biomedicina de Sevilla, University of Sevilla, Sevilla, Spain 41013; Department of Endocrinology (F.J.T.), Hospital Virgen de la Victoria, and Department of Endocrinology (J.A.G.-A.), Hospital Carlos Haya, Malaga, Spain 29010; and CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn) 15706, spain (A.I.-C., F.J.T., P.B., I.B., C.D., R.M.L., J.P.C., C.V.A.), Spain 15706.
authors.forename: Esther
authors.initials: E
authors.lastname: Diaz-Rodriguez
authors.forename: Angela R
authors.initials: AR
authors.lastname: Garcia-Rendueles
authors.forename: Alejandro
authors.initials: A
authors.lastname: Ibáñez-Costa
authors.forename: Ester
authors.initials: E
authors.lastname: Gutierrez-Pascual
authors.forename: Montserrat
authors.initials: M
authors.lastname: Garcia-Lavandeira
authors.forename: Alfonso
authors.initials: A
authors.lastname: Leal
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Japon
authors.forename: Alfonso
authors.initials: A
authors.lastname: Soto
authors.forename: Eva
authors.initials: E
authors.lastname: Venegas
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Tinahones
authors.forename: Juan A
authors.initials: JA
authors.lastname: Garcia-Arnes
authors.forename: Pedro
authors.initials: P
authors.lastname: Benito
authors.forename: Maria
authors.initials: M
authors.lastname: Angeles Galvez
authors.forename: Luis
authors.initials: L
authors.lastname: Jimenez-Reina
authors.forename: Ignacio
authors.initials: I
authors.lastname: Bernabeu
authors.forename: Carlos
authors.initials: C
authors.lastname: Dieguez
authors.forename: Raul M
authors.initials: RM
authors.lastname: Luque
authors.forename: Justo P
authors.initials: JP
authors.lastname: Castaño
authors.forename: Clara V
authors.initials: CV
authors.lastname: Alvarez
mesh_terms: D000236:Adenoma / Q000235:genetics / Q000473:pathology*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000494:pharmacology*; D049912:Growth Hormone-Secreting Pituitary Adenoma / Q000235:genetics / Q000473:pathology*; D006801:Humans; D010911:Pituitary Neoplasms / Q000235:genetics / Q000473:pathology*; D051096:Proto-Oncogene Proteins c-ret / Q000502:physiology; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D050817:Transcription Factor Pit-1 / Q000502:physiology; D014407:Tumor Cells, Cultured; D025803:Tumor Suppressor Protein p14ARF / Q000502:physiology; D016159:Tumor Suppressor Protein p53 / Q000502:physiology
chemical_list: D051100:Glial Cell Line-Derived Neurotrophic Factor; C494187:POU1F1 protein, human; D050817:Transcription Factor Pit-1; D025803:Tumor Suppressor Protein p14ARF; D016159:Tumor Suppressor Protein p53; D051096:Proto-Oncogene Proteins c-ret; C099282:RET protein, human