The expression of the pituitary adenylate cyclase-activating polypeptide/vasoactive intestinal polypeptide (PACAP/VIP) receptor subtypes was evaluated in the normal rat pituitary gland and in different rat spontaneous transplantable SMtTW tumours (SMtTW2 which expresses prolactin (PRL), SMtTW10 which expresses GH and SMtTW3 which expresses both PRL and GH) by measurement of PACAP/VIP-stimulated adenylate cyclase activity and detection of the presence of mRNA coding for the different receptor forms. In normal glands, the order of potency of the peptides suggested that adenylate cyclase activity was mediated through interaction with PACAP selective receptors (PACAP I receptors); mRNAs coding for the PACAP I receptor, but also for the PACAP II VIP2 receptor, were detected. In SMtTW2 tumours, the functional response was close to that observed in the presence of PACAP II VIP2 receptors; mRNAs coding for PACAP I and PACAP II VIP1 and PACAP II VIP2 receptors were detected. In the SMtTW10 tumours, the functional response was complex but compatible with the involvement of PACAP I and PACAP II receptors; mRNAs coding for the PACAP I and PACAP II VIP1 receptors were detected. In the SMtTW3 tumour, the profile was similar to that of the normal pituitary gland and the mRNA coding for the PACAP I receptor only was detected. Thus, while the control of normal pituitary gland adenylate cyclase activity by PACAP and VIP was mediated by PACAP-selective receptors, in spontaneous transplantable tumours a variable profile was observed and PACAP, as well as VIP1 and VIP2 receptors, may contribute to the responses.
Adenomas can develop from each cell type of the anterior pituitary. In the normal pituitary, three of these cell types, the GH-, prolactin- and TSH-secreting cells, express the transcription factor Pit-1/GHF-1 which is responsible for prolactin and GH (and probably TSH) cell commitment, differentiation, probably proliferation and gene expression. We have analysed the expression of Pit-1/GHF-1 in a panel of human pituitary adenomas. All GH-, prolactin- and TSH-expressing adenomas studied expressed the Pit-1/GHF-1 factor, as demonstrated by in-situ hybridization and immunocytochemistry. The expression was higher in adenomas than in normal human pituitary. In contrast, ACTH- and LH—FSH-secreting and non-secreting adenomas were negative. Seven transplants of the spontaneous rat prolactinoma SMtTW were also investigated and all were found to be positive.
This further stresses the analogy between these tumours and human prolactinomas. Taken together, the data confirm that Pit-1/GHF-1 expression is restricted to GH-, prolactin- and TSH-expressing cells, and the increased expression in adenomas is compatible with a role of Pit-1/GHF-1 in cell proliferation.
We have combined different techniques to analyse passages of five different rat spontaneous pituitary tumours (SMtTW) that were transplanted under the kidney capsule. These tumours were secreting prolactin (PRL), GH or both hormones. RIA, immunocytochemistry (ICC) and Western blot analysis were applied to characterize the hormone(s) stored (ICC and Western blot) and secreted (RIA). mRNA content was analysed by PCR, Northern blot analysis and in situ hybridization.
The data point not only to the reliability of the techniques used at both protein and RNA levels for each tumour studied but also to the complementarity of some techniques. For example, whereas Northern blot analysis demonstrates the presence and size of hormone mRNA, in situ hybridization indicates the percentage of cells expressing a given hormone mRNA and allows the presence of one population (or more) of cells in a given tumour to be identified.
Moreover, the tumours were compared with normal rat pituitary. Although the PRL and GH mRNAs were identical in size, the amount of mRNA was lower in the tumours. At the protein level, the PRL and GH variants exhibited a different pattern of expression in tumours compared with the normal rat pituitary.
The biological significance of these differences is discussed.