Clinical studies have defined the core 'genetic blueprint' of a cancer cell, but this information does not necessarily predict the cancer phenotype. Signalling hubs that mediate such phenotype have been identified largely using OMICS platforms that measure dynamic molecular changes within the cancer cell landscape. The pro-oncogenic protein anterior gradient 2 (AGR2) is a case in point; AGR2 has been shown using a range of expression platforms to be involved in asthma, inflammatory bowel disease, cell transformation, cancer drug resistance and metastatic growth. AGR2 protein is also highly overexpressed in a diverse range of human cancers and can be secreted and detected in extracellular fluids, thus representing a compelling pro-oncogenic signalling intermediate in human cancer. AGR2 belongs to the protein disulphide isomerase family with all the key features of an endoplasmic reticulum-resident protein-this gives clues into how it might function as an oncoprotein through the regulation of protein folding, maturation and secretion that can drive metastatic cell growth. In this review, we will describe the known aspects of AGR2 molecular biology, including gene structure and regulation, emerging protein interaction networks and how its subcellular localization mediates its biological functions. We will finally review the cases of AGR2 expression in human cancers, the pathophysiological consequences of AGR2 overexpression, its potential role as a tumour biomarker that predicts the response to therapy and how the AGR2 pathway might form the basis for drug discovery programmes aimed at targeting protein folding/maturation pathways that mediate secretion and metastasis.

For over three decades, renal physiology has sought a putative natriuretic hormone (third factor) that might control the body's pool of extracellular fluid, an important determinant in hypertension, congestive heart failure, and cirrhosis. In our search for this hormone, we have isolated several pure natriuretic factors from human uremic urine that would appear, alone or in combination, to mark a cluster of phenomena previously presumed to be that of a single "natriuretic hormone." This paper reports the purification, chemical structure, and total synthesis of the first of these compounds, LLU-a, which proved to be 2,7,8-trimethyl-2-(pcarboxyethyl)-6-hydroxychroman, presumably a metabolite of y-tocopherol. Both natural LLU-a and synthetic material are identical (except for optical activity) with respect to structure and biological activity. It appears that the natriuretic activity of LLU-a is mediated by inhibition of the 70 pS K+ channel in the apical membrane of the thick ascending limb of the kidney.As a result of salt-induced plasma-volume expansion in mammals, three concurrent events have been observed: sustained natriuresis, rising plasma concentration of a Na+ transport inhibitor, and pressor activity. It has been presumed that these effects are due to elaboration of a low-molecular-weight "natriuretic hormone," the putative controller of extracellular fluid (1). Over 30 years of effort have failed to characterize the putative hormone (2, 3). Atrial natriuretic factor, when infused, produces a natriuresis and a decrease in blood pressure that are short-lived (4, 5) and whose physiological role is still undefined (6, 7).The approach of essentially all other workers has been to investigate mammalian-derived isolates that inhibit the Na+ pump (2,8). From these studies, digoxin (9) and "iso-ouabain" (10-13) have been isolated; however, digoxin and ouabain lead to kaliuresis (4,(14)(15)(16)(17). Therefore, we hypothesized that this search tool is an inadequate marker for natriuresis. Consequently, a natriuretic assay has been developed in which the in vivo physiological events, urine volume, K+ and Na+ concentrations, and mean arterial pressure are measured (18).In this paper, we report the isolation of pure LLU-a, the determination of its structure by spectroscopy, its synthesis in racemic form, and its biological characterization. Given its structure, we infer that it is the product of in vivo oxidative metabolism of y-tocopherol, a member of the vitamin E complex. MATERIALS AND METHODSPurification of LLU-a. Human uremic urine (800 liters) was collected, processed by ultrafiltration (3 kDa) and lyophilization, and then chromatographed on Sephadex G-25 to obtain the post-salt fraction as described (18 Step 1. Reversed-phase HPLC was performed by gradient elution with 0.2 M pyridinium acetate, pH 5.5, and methanol as described (4). Based on bioassay data, fractions 50-80 were combined for further purification.Step 2. The next column (5 pm; 10 x 250 mm) was eluted at 2 ml/min with a gradient formed from...

Transcriptomic screens in breast cancer cell lines have identified a protein named anterior gradient-2 (AGR2) as a potentially novel oncogene overexpressed in estrogen receptor (ER) positive tumours. As targeting the ER is responsible for major improvements in cure rates and prevention of breast cancers, we have evaluated the prooncogenic function of AGR2 in anti-hormone therapeutic responses. We show that AGR2 expression promotes cancer cell survival in clonogenic assays and increases cell proliferation and viability in a range of cancer cell lines. Chromatin immunoprecipitation and reporter assays indicate that AGR2 is transcriptionally activated by estrogen through ERa. However, we also found that AGR2 expression is elevated rather than inhibited in response to tamoxifen, thus identifying a novel mechanism to account for an agonistic effect of the drug on a specific pro-oncogenic pathway. Consistent with these data, clinical analysis indicates that AGR2 expression is related to treatment failure in ERapositive breast cancers treated with tamoxifen. In contrast, AGR2 is one of the most highly suppressed genes in cancers of responding patients treated with the anti-hormonal drug letrozole. These data indicate that the AGR2 pathway represents a novel pro-oncogenic pathway for evaluation as anti-cancer drug developments, especially therapies that by-pass the agonist effects of tamoxifen.

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