Localization of Inhibins and Activins in Normal Endocrine Cells and Endocrine Tumors of the Gut and Pancreas: An Immunohistochemical and in Situ Hybridization Study

Activins and inhibins, which belong to the TGFβ family, are composed of different combinations of α-, βA-, and βB-subunits, resulting in inhibin A (αβA), inhibin B (αβB), activin A (βAβA), activin B (βBβB), and activin AB (βAβB). They regulate several cell functions, acting as paracrine/autocrine factors. Their actions, which depend on binding to specific receptors, are also modulated by follistatin. Gastroenteropancreatic (GEP) endocrine cells and endocrine tumors (ETs) produce several growth factors, but it is not well known whether they express follistatin and the various inhibin/activin subunits. We studied their expression in 65 GEP ETs using immunohistochemistry (IHC) and in situ hybridization (ISH). The α-subunit and follistatin were not identified in normal GEP endocrine cells and were poorly expressed in ETs. A βA-subunit immunoreactivity (IR) was detected in A-, G-, EC-, and GIP-cells, while βB-chain IR was present only in D-cells. The mRNAs encoding for these molecules were poorly expressed in normal tissues. βA- and βB-subunits were identified in several ETs by both IHC and ISH: βA-subunit mainly in G-cell and A-cell ETs, and βB-subunit in D-cell, A-cell, and EC-cell ETs. Our results demonstrate a differential expression of activin/inhibin subunits among different types of GEP endocrine cells and related tumors, suggesting a role in modulation of biological functions of these normal and neoplastic endocrine cells.