Isolation of antibody to human placental alkaline phosphatase (PLAP) from extracts of human placentae.

PROBLEM: Human placental alkaline phosphatase (PLAP) is a unique placental antigen bound to the syncytiotrophoblast, which may be able to elicit a specific immune response in pregnancy. METHOD OF STUDY: Antibody to PLAP was purified from placental extracts by: a) acid elution of membrane vesicles; b) purifying complexes of PLAP with human antibody on monoclonal antibodies to PLAP followed by denaturation of the enzyme; and c) by denaturation of PLAP in placental extracts and purification of antibody to PLAP on PLAP columns. RESULTS AND CONCLUSIONS: Specific antibody to PLAP is present in placental extracts, and is mostly bound to placental membrane preparations. PLAP is therefore immunogenic in pregnancy and could serve as a useful monitor of pregnancy-specific immunological responses. Since a similar enzyme appears in some cancers, it is possible that the immunization against PLAP in pregnancy will help to protect against the development of ovarian and endometrial cancer (the 'fetal antigen' hypothesis).

Epstein-Barr virus small RNAs potentiate tumorigenicity of Burkitt lymphoma cells independently of an effect on apoptosis.

The tumorigenic potential of the Burkitt lymphoma (BL) cell line Akata is dependent on the restricted latency program of Epstein-Barr virus (EBV) that is characteristically maintained in BL tumors. Within these cells, EBV-mediated inhibition of apoptosis correlates with an up-regulation of BCL-2 levels in concert with a down-regulation in c-MYC expression that occurs under growth-limiting conditions. Here we addressed whether EBV's effects on apoptosis and tumorigenicity are mediated by the EBV small RNAs EBER-1 and EBER-2. Stable expression of the EBERs in EBV-negative Akata BL cells, at levels comparable to those in EBV-positive cells, significantly enhanced the tumorigenic potential of EBV-negative BL cells in SCID mice, but did not fully restore tumorigenicity relative to EBV-positive Akata cells. Furthermore, wild-type or greater levels of EBER expression in EBV-negative Akata cells did not promote BL cell survival. These data therefore suggest that EBV can contribute to BL through at least two avenues: an EBER-dependent mechanism that enhances tumorigenic potential independent of a direct effect on apoptosis, and a second mechanism, mediated by an as-yet-unidentified EBV gene(s), that offsets the proapoptotic consequences of deregulated c-MYC in BL.

Epstein-barr virus regulates c-MYC, apoptosis, and tumorigenicity in Burkitt lymphoma.

Loss of the Epstein-Barr virus (EBV) genome from Akata Burkitt lymphoma (BL) cells is coincident with a loss of malignant phenotype, despite the fact that Akata and other EBV-positive BL cells express a restricted set of EBV gene products (type I latency) that are not known to overtly affect cell growth. Here we demonstrate that reestablishment of type I latency in EBV-negative Akata cells restores tumorigenicity and that tumorigenic potential correlates with an increased resistance to apoptosis under growth-limiting conditions. The antiapoptotic effect of EBV was associated with a higher level of Bcl-2 expression and an EBV-dependent decrease in steady-state levels of c-MYC protein. Although the EBV EBNA-1 protein is expressed in all EBV-associated tumors and is reported to have oncogenic potential, enforced expression of EBNA-1 alone in EBV-negative Akata cells failed to restore tumorigenicity or EBV-dependent down-regulation of c-MYC. These data provide direct evidence that EBV contributes to the tumorigenic potential of Burkitt lymphoma and suggest a novel model whereby a restricted latency program of EBV promotes B-cell survival, and thus virus persistence within an immune host, by selectively targeting the expression of c-MYC.