R. Parrotta

Functional Role and Prognostic Significance of CD157 in Ovarian Carcinoma

BACKGROUND CD157, an ADP-ribosyl cyclase-related cell surface molecule, regulates leukocyte diapedesis during inflammation. Because CD157 is expressed in mesothelial cells and diapedesis resembles tumor cell migration, we investigated the role of CD157 in ovarian carcinoma. METHODS We assayed surgically obtained ovarian cancer and mesothelial cells and both native and engineered ovarian cancer cell lines for CD157 expression using flow cytometry and reverse transcription-polymerase chain reaction (RT-PCR), and for adhesion to extracellular matrices, migration, and invasion using cell-based assays. We investigated invasion of human peritoneal mesothelial cells by serous ovarian cancer cells with a three-dimensional coculture model. Experiments were performed with or without CD157-blocking antibodies. CD157 expression in tissue sections from ovarian cancer patients (n = 88) was examined by immunohistochemistry, quantified by histological score (H score), and categorized as at or above or below the median value of 60, and compared with clinical parameters. Statistical tests were two-sided. RESULTS CD157 was expressed by ovarian cancer cells and mesothelium, and it potentiated the adhesion, migration, and invasion of serous ovarian cancer cells through different extracellular matrices. CD157-transfected ovarian cancer cells migrated twice as much as CD157-negative control cells (P = .001). Blockage of CD157 inhibited mesothelial invasion by serous ovarian cancer cells in a three-dimensional model. CD157 was expressed in 82 (93%) of the 88 epithelial ovarian cancer tissue specimens. In serous ovarian cancer, patients with CD157 H scores of 60 or greater had statistically significantly shorter disease-free survival and overall survival than patients with lower CD157 H scores (CD157 H score > or =60 vs <60: median disease-free survival = 18 months, 95% confidence interval [CI] = 5.92 to 30.07 vs unreached, P = .005; CD157 H score > or =60 vs <60: median overall survival = 45 months, 95% CI = 21.21 to 68.79 vs unreached, P = .024). Multivariable Cox regression showed that CD157 is an independent prognostic factor for recurrence (hazard ratio of disease recurrence = 3.01, 95% CI = 1.35 to 6.70, P = .007) and survival (hazard ratio of survival = 3.44, 95% CI = 1.27 to 9.31, P = .015). CONCLUSIONS CD157 plays a pivotal role in the control of ovarian cancer cell migration and peritoneal invasion, and it may be clinically useful as a prognostic tool and therapeutic target.

The CD157-Integrin Partnership Controls Transendothelial Migration and Adhesion of Human Monocytes

CD157, a member of the CD38 gene family, is an NAD-metabolizing ectoenzyme and a signaling molecule whose role in polarization, migration, and diapedesis of human granulocytes has been documented; however, the molecular events underpinning this role remain to be elucidated. This study focused on the role exerted by CD157 in monocyte migration across the endothelial lining and adhesion to extracellular matrix proteins. The results demonstrated that anti-CD157 antibodies block monocyte transmigration and adhesion to fibronectin and fibrinogen but that CD157 cross-linking is sufficient to overcome the block, suggesting an active signaling role for the molecule. Consistent with this is the observation that CD157 is prevalently located within the detergent-resistant membrane microdomains to which, upon clustering, it promotes the recruitment of β1 and β2 integrin, which, in turn, leads to the formation of a multimolecular complex favoring signal transduction. This functional cross-talk with integrins allows CD157 to act as a receptor despite its intrinsic structural inability to do so on its own. Intracellular signals mediated by CD157 rely on the integrin/Src/FAK (focal adhesion kinase) pathway, resulting in increased activity of the MAPK/ERK1/2 and the PI3K/Akt downstream signaling pathways, which are crucial in the control of monocyte transendothelial migration. Collectively, these findings indicate that CD157 acts as a molecular organizer of signaling-competent membrane microdomains and that it forms part of a larger molecular machine ruled by integrins. The CD157-integrin partnership provides optimal adhesion and transmigration of human monocytes.

Overexpression of CD157 contributes to epithelial ovarian cancer progression by promoting mesenchymal differentiation.

Epithelial ovarian carcinoma (EOC) is an aggressive tumor often diagnosed at an advanced stage, when there is little or no prospect of cure. Despite advances in surgical and chemotherapeutic strategies, only marginal improvements in patient outcome have been obtained. Hence, unraveling the biological mechanisms underpinning EOC progression is critical for improving patients’ survival. Recently, we reported that CD157 (an ectoenzyme regulating leukocyte diapedesis) is expressed in EOC and that high expression of the molecule is negatively correlated with the disease outcome in patients. Here, we demonstrate that forced overexpression of CD157 in OVCAR-3, TOV-21G, A2780 and OV-90 ovarian cancer cell lines promotes morphological and phenotypic changes characterized by disruption of intercellular junctions, downregulation of epithelial markers and upregulation of mesenchymal ones. These changes in cell shape and phenotype bring to reduced sensitivity to anoikis, increased anchorage-independent growth, cell motility and mesothelial invasion. Conversely, knockdown of CD157 in OV-90 and OC314 cells reverts the mesenchymal phenotype and reduces the cells’ migratory potential. Transcriptome profiling analysis highlighted 378 significantly differentially expressed genes, representing the signature of CD157-overexpressing OVCAR-3 and OV-90 cells. The modulation of selected genes translates into alteration of protein expression that give cells a highly malignant phenotype. The overall picture deduced from the analysis of the modulated transcripts is that high expression of CD157 strengthens a number of biological processes favoring tumor progression (including development and cell motility), and weakens several biological processes hindering tumor progression (such as apoptosis, cell death and response to stress). Together, these findings implicate CD157 in the progression of EOC to metastatic disease and suggest that CD157 may represent a valuable therapeutic target.

Human canonical CD157/Bst1 is an alternatively spliced isoform masking a previously unidentified primate-specific exon included in a novel transcript

CD157/Bst1 is a dual-function receptor and β-NAD+-metabolizing ectoenzyme of the ADP-ribosyl cyclase family. Expressed in human peripheral blood neutrophils and monocytes, CD157 interacts with extracellular matrix components and regulates leukocyte diapedesis via integrin-mediated signalling in inflammation. CD157 also regulates cell migration and is a marker of adverse prognosis in epithelial ovarian cancer and pleural mesothelioma. One form of CD157 is known to date: the canonical sequence of 318 aa from a 9-exon transcript encoded by BST1 on human chromosome 4. Here we describe a second BST1 transcript, consisting of 10 exons, in human neutrophils. This transcript includes an unreported exon, exon 1b, located between exons 1 and 2 of BST1. Inclusion of exon 1b in frame yields CD157-002, a novel proteoform of 333 aa: exclusion of exon 1b by alternative splicing generates canonical CD157, the dominant proteoform in neutrophils and other tissues analysed here. In comparative functional analyses, both proteoforms were indistinguishable in cell surface localization, specific mAb binding, and behaviour in cell adhesion and migration. However, NAD glycohydrolase activity was detected in canonical CD157 alone. Comparative phylogenetics indicate that exon 1b is a genomic innovation acquired during primate evolution, pointing to the importance of alternative splicing for CD157 function.

Biological role, clinical significance and potential therapeutic applications of CD157 in ovarian cancer

Ovarian cancer is the leading cause of gynecologic cancer-related morbidity and mortality owing to the difficulty in detecting early-stage disease. Despite advances in surgical and chemotherapeutic strategies, only marginal improvement in patient outcome has been achieved. Hence, understanding the biological mechanisms underlying ovarian cancer development and progression is critical for its treatment. We reported that CD157 (also known as BST-1), a NAD-metabolizing ectoenzyme regulating leukocyte diapedesis in inflammatory conditions, is expressed in approximately 90% of epithelial ovarian cancers and high CD157 expression is associated with poor outcome in patients. Our experimental results showed that CD157 controls ovarian cancer progression by promoting mesenchymal differentiation. The increased aggressiveness associated with tumors with high CD157 can be reverted in vitro by CD157 gene silencing, or by monoclonal antibodies that block CD157. The overall picture inferred from our experimental and clinical findings suggests that CD157 could aid diagnosis by classifying ovarian cancers into molecular subtypes with different outcomes, CD157 could also represent a novel candidate as a target of antibody-based therapies. This review summarizes and assesses recent research into the emerging functions of CD157 in the control of ovarian cancer progression.

Ectoenzymes in Epithelial Ovarian Carcinoma: Potential Diagnostic Markers and Therapeutic Targets

Ovarian cancer is one of the most lethal among the gynaecological malignancies, affecting 12% of women in developed countries (Cannistra, 2004). The lethality of ovarian cancer is primarily attributable to our current inability to detect the disease at an early stage, when it is still limited to the ovary. Therefore, the majority of patients are diagnosed when they have advanced-stage disease. Despite progresses in cytotoxic therapies, only 30% of patients with advanced-stage ovarian cancer survive 5 years after diagnosis. The insidious nature of ovarian cancer stems from its unique biological behaviour: ovarian carcinoma can spread by direct extension to adjacent organs, and exfoliated tumour cells can be transported in peritoneal fluid (Naora et al., 2005). Subsequent implants are characterised by their adhesion to mesothelial cells, migration throughout and invasion of the tumor cells into the omentum and peritoneum. This seeding of the peritoneal cavity is frequently associated with ascites formation. Only secondarily and rather late during the disease progression, are pelvic and para-aortic lymph nodes involved. However, the local peritoneal disease cannot be controlled and remains a factor leading to death (Feki et al., 2009). The cellular processes that lead to local and distant dissemination of ovarian cancer are not fully understood, and the mechanisms of interaction between cancer cells and mesothelium need to be further elucidated to achieve novel information on the biology of this highly aggressive form of cancer and possibly, to identify new potential targets for selective therapeutic strategies. The combined effort of clinicians and researchers has led to the identification of a number of molecules that might facilitate screening, diagnosis, prognosis and monitoring response to treatment or relapse during follow-up. These new molecules might provide specific targets for anti-tumour therapy with antibody-directed treatments, gene therapy or specific inhibitory molecules. An unexpectedly high number of these newly identified molecules have turned out to be cell surface-expressed ectoenzymes. Ectoenzymes are a large, heterogeneous class of membrane proteins whose catalytically active sites face the extracellular environment. The products of their catalytic activities can influence the extracellular environment (for example, several of these products can function as second messengers or regulate the recruitment of cells). Moreover, many ectoenzymes can function