title: Proliferation of transformed somatotroph cells related to low or absent expression of protein kinase a regulatory subunit 1A protein.
abstract: The two regulatory subunits (R1 and R2) of protein kinase A (PKA) are differentially expressed in cancer cell lines and exert diverse roles in growth control. Recently, mutations of the PKA regulatory subunit 1A gene (PRKAR1A) have been identified in patients with Carney complex. The aim of this study was to evaluate the expression of the PKA regulatory subunits R1A, R2A, and R2B in a series of 30 pituitary adenomas and the effects of subunit activation on cell proliferation. In these tumors, neither mutation of PRKAR1A nor loss of heterozygosity was identified. By real-time PCR, mRNA of the three subunits was detected in all of the tumors, R1A being the most represented in the majority of samples. By contrast, immunohistochemistry documented low or absent R1A levels in all tumors, whereas R2A and R2B were highly expressed, thus resulting in an unbalanced R1/R2 ratio. The low levels of R1A were, at least in part, due to proteasome-mediated degradation. The effect of the R1/R2 ratio on proliferation was assessed in GH3 cells, which showed a similar unbalanced pattern of R subunits expression, and in growth hormone-secreting adenomas. The R2-selective cAMP analog 8-Cl cAMP and R1A RNA silencing, stimulated cell proliferation and increased Cyclin D1 expression, respectively, in human and rat adenomatous somatotrophs. These data show that a low R1/R2 ratio promoted proliferation of transformed somatotrophs and are consistent with the Carney complex model in which R1A inactivating mutations further unbalance this ratio in favor of R2 subunits. These results suggest that low expression of R1A protein may favor cAMP-dependent proliferation of transformed somatotrophs.
authors.affiliation: Institute of Endocrine Sciences, Ospedale Maggiore, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Milan, Italy.
authors.forename: Andrea G
authors.initials: AG
authors.lastname: Lania
authors.forename: Giovanna
authors.initials: G
authors.lastname: Mantovani
authors.forename: Stefano
authors.initials: S
authors.lastname: Ferrero
authors.forename: Caterina
authors.initials: C
authors.lastname: Pellegrini
authors.forename: Sara
authors.initials: S
authors.lastname: Bondioni
authors.forename: Erika
authors.initials: E
authors.lastname: Peverelli
authors.forename: Paola
authors.initials: P
authors.lastname: Braidotti
authors.forename: Marco
authors.initials: M
authors.lastname: Locatelli
authors.forename: Mario L
authors.initials: ML
authors.lastname: Zavanone
authors.forename: Emanuela
authors.initials: E
authors.lastname: Ferrante
authors.forename: Silvano
authors.initials: S
authors.lastname: Bosari
authors.forename: Paolo
authors.initials: P
authors.lastname: Beck-Peccoz
authors.forename: Anna
authors.initials: A
authors.lastname: Spada
mesh_terms: D000236:Adenoma / Q000201:enzymology* / Q000473:pathology*; D048708:Cell Growth Processes / Q000187:drug effects / Q000502:physiology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; D017868:Cyclic AMP-Dependent Protein Kinases; D019938:Cyclin D1 / Q000096:biosynthesis; D004789:Enzyme Activation; D005091:Exons; D006801:Humans; D007150:Immunohistochemistry; D007438:Introns; D008247:Lysosomes / Q000187:drug effects; D010911:Pituitary Neoplasms / Q000201:enzymology* / Q000473:pathology*; D061988:Proteasome Inhibitors; D021122:Protein Subunits; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
chemical_list: D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; C517834:PRKAR1A protein, human; C517836:Prkar1a protein, rat; D061988:Proteasome Inhibitors; D021122:Protein Subunits; D011506:Proteins; D019938:Cyclin D1; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases