Differential somatostatin receptor (SSTR) 1–5 expression and downstream effectors in histologic subtypes of growth hormone pituitary tumors

Abstract

PurposeThe aim of this study was to examine whether differential expression of somatostatin receptors (SSTR) 1–5 and downstream effectors are different in densely (DG) and sparsely (SG) granulated histological growth hormone (GH) pituitary tumor subtypes. MethodsThe study included 33 acromegalic patients with 23 DG and 10 SG tumors. SSTR1–5 were measured by qPCR and immunoblotting. Signaling candidates downstream of SSTR2 were also assessed. ResultsSSTR2 mRNA and protein levels were significantly higher in DG compared to SG tumors. Downstream of SSTR2, p27kip1 was decreased (2.6-fold) in SG compared to DG tumors, suggesting a potential mechanism of SSA resistance in SG tumors with intact SSTR2 expression. Re-expression of E-cadherin in GH pituitary cell increased p27kip1 levels. ConclusionsHistological subtyping correlated with SSTR2, E cadherin and p27kip protein levels and these may serve as useful biomarkers in GH tumors to predict behavior and response to therapy with SSA.