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L-J Chew, V Seah, D Murphy, and D Carter


It is well established that oestrogens can stimulate prolactin (PRL) secretion as well as the expression of the vasoactive intestinal peptide (VIP) gene whose product is also a potent PRL secretagogue. Previous evidence has supported both an autocrine and a paracrine role for pituitary VIP in PRL release in vitro; however, the cellular origin of VIP in pituitary tissue still remains poorly defined. In these studies, we have demonstrated by in situ hybridisation that VIP RNA is detected in the anterior pituitaries of chronically hyperoestrogenised rats, but not in those of untreated animals. Using a double-probe labelling procedure, VIP RNA has been shown to be present in a subpopulation of PRL-producing cells, while colocalisation of VIP and GH RNA was not observed. VIP gene expression in the rat anterior pituitary gland was characterised by the presence of two alternatively polyadenylated transcripts, 1·7 kb and 1·0 kb in size. We have generated a probe specific for the 1·7 kb transcript and double-labelling studies also showed definitive colocalisation with PRL mRNA. Our results demonstrating the presence of VIP RNA in PRL-producing cells thus suggest that VIP may play an autocrine role in PRL hypersecretion under conditions of oestrogen-induced hyperplasia.

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J S Davies, J L Holter, D Knight, S M Beaucourt, D Murphy, D A Carter, and T Wells

Targeted overexpression of biologically active peptides represents a powerful approach to the functional dissection of neuroendocrine systems. However, the requirement to generate separate, biologically active and reporter molecules necessitates the use of internal ribosome entry site (IRES) technology, which often results in preferential translation of the second cistron. We report here a novel approach in which the proteolytic processing machinery of the regulated secretory pathway (RSP) has been exploited to generate multiple mature proteins from a monocistronic construct that encodes a single precursor. This was achieved by duplication of the pre-pro cleavage sites in pre-prosomatostatin cDNA. The duplicated site included 10 flanking amino acids on either side of the Gly-Ala cleavage position. This enabled the incorporation of a foreign protein-coding sequence (in this case, enhanced green fluorescent protein (eGFP)) between these sites. The pre-eGFP-prosomatostatin (PEPS) construct generated co-localized expression of fully processed eGFP and somatostatin to the RSP of transiently transfected AtT20 cells. This approach represents an advance upon bicistronic and other extant approaches to the targeting of multiple, biologically active proteins to neuroendocrine systems, and, importantly, permits the co-expression of fluorescent markers with biologically active neuropeptides. In this study, our demonstration of the fusion of the first 10 amino acids of the prosomatostatin sequence to the N-terminus of eGFP shows that this putative sorting sequence is sufficient to direct expression to the RSP.

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J G Moggs, T C Murphy, F L Lim, D J Moore, R Stuckey, K Antrobus, I Kimber, and G Orphanides

Estrogen receptor (ER)-negative breast carcinomas do not respond to hormone therapy, making their effective treatment very difficult. The re-expression of ERα in ER-negative MDA-MB-231 breast cancer cells has been used as a model system, in which hormone-dependent responses can be restored. Paradoxically, in contrast to the mitogenic activity of 17β-estradiol (E2) in ER-positive breast cancer cells, E2 suppresses proliferation in ER-negative breast cancer cells in which ERα has been re-expressed. We have used global gene expression profiling to investigate the mechanism by which E2 suppresses proliferation in MDA-MB-231 cells that express ERα through adenoviral infection. We show that a number of genes known to promote cell proliferation and survival are repressed by E2 in these cells. These include genes encoding the anti-apoptosis factor SURVIVIN, positive cell cycle regulators (CDC2, CYCLIN B1, CYCLIN B2, CYCLIN G1, CHK1, BUB3, STK6, SKB1, CSE1 L) and chromosome replication proteins (MCM2, MCM3, FEN1, RRM2, TOP2A, RFC1). In parallel, E2-induced the expression of the negative cell cycle regulators KIP2 and QUIESCIN Q6, and the tumour-suppressor genes E-CADHERIN and NBL1. Strikingly, the expression of several of these genes is regulated in the opposite direction by E2 compared with their regulation in ER-positive MCF-7 cells. Together, these data suggest a mechanism for the E2-dependent suppression of proliferation in ER-negative breast cancer cells into which ERα has been reintroduced.