Pregnancy-specific glycoprotein function, conservation and receptor investigation

Pregnancy-specific glycoproteins (PSGs) are highly glycosylated secreted proteins encoded by multi-gene families in some placental mammals. They are carcinoembryonic antigen (CEA) family and immunoglobulin (Ig) superfamily members. PSGs are immunomodulatory, and have been demonstrated to possess antiplatelet and pro-angiogenic properties. Low serum levels of these proteins have been correlated with adverse pregnancy outcomes. Objectives: Main research goals of this thesis were: 1). To attempt to replicate previously reported cytokine responses to PSG-treatment of immune cells and subsequently to investigate functionally important amino acids within PSG1. 2). To determine whether candidate receptor, integrin αvβ3, was a binding partner for PSG1 and to investigate whether PSG1 possessed functionality in a leukocyte-endothelial interaction assay. 3). To determine whether proteins generated from recently identified putative PSG genes in the horse shared functional properties with PSGs from other species. Outcomes: 1). Sequential domain deletion of PSG1 as well as mutation of conserved residues within the PSG1 Ndomain did not affect PSG1-induced TGF-β1. The investigated response was subsequently found to be the result of latent TGF-β1 contaminating the recombinant protein. Protein further purified by SEC to remove this showed no induction of TGF-β1. The most N-terminal glycosylation site was demonstrated to have an important role in PSG N domain secretion. PSG1 attenuated LPS-induced IL-6 and TNF-α. Investigations into signalling underpinning this proved inconclusive. 2). Integrin αvβ3 was identified as a novel PSG1 receptor mediating an as yet unknown function. Preliminary investigations into a role for PSGs as inhibitors of leukocyte endothelial interactions showed no effect by PSG1. 3). Horse PSG protein, CEACAM49, was shown to be similarly contaminated by latent TGF-β1 particle and once removed did not demonstrate TGF-β1 release. Interestingly horse PSG did show anti-platelet properties through inhibition of the plateletfibrinogen interaction as previously published for mouse and human PSGs

Pregnancy-specific glycoprotein expression in normal gastrointestinal tract and in tumors detected with novel monoclonal antibodies

Pregnancy-specific glycoproteins (PSGs) are immunoglobulin superfamily members related to the carcinoembryonic antigen-related cell adhesion molecule (CEACAM) family and are encoded by 10 genes in the human. They are secreted at high levels by placental syncytiotrophoblast into maternal blood during pregnancy, and are implicated in immunoregulation, thromboregulation, and angiogenesis. To determine whether PSGs are expressed in tumors, we characterized 16 novel monoclonal antibodies to human PSG1 and used 2 that do not cross-react with CEACAMs to study PSG expression in tumors and in the gastrointestinal (GI) tract using tissue arrays and immunohistochemistry. Staining was frequently observed in primary squamous cell carcinomas and colonic adenocarcinomas and was correlated with the degree of tumor differentiation, being largely absent from metastatic samples. Staining was also observed in normal oesophageal and colonic epithelium. PSG expression in the human and mouse GI tract was confirmed using quantitative RT-PCR. However, mRNA expression was several orders of magnitude lower in the GI tract compared to placenta. Our results identify a non-placental site of PSG expression in the gut and associated tumors, with implications for determining whether PSGs have a role in tumor progression, and utility as tumor biomarkers