The Epstein-Barr virus BNLF-1 membrane protein LMP1 induces homotypic adhesion mediated by CD11a/CD18 in a murine B-cell line, mimicking the action of phorbol ester

Evaluation of LMP1 of Epstein-Barr virus as a therapeutic target by its inhibition

BACKGROUND

The latent membrane protein-1 (LMP1) encoded by Epstein-Barr virus (EBV) is an oncoprotein which acts by constitutive activation of various signalling pathways, including NF-kappaB. In so doing it leads to deregulated cell growth intrinsic to the cancer cell as well as having extrinsic affects upon the tumour microenvironment. These properties and that it is a foreign antigen, lead to the proposition that LMP1 may be a good therapeutic target in the treatment of EBV associated disease. LMP1 is expressed in several EBV-associated malignancies, notably in Hodgkin's lymphoma and nasopharyngeal carcinoma (NPC). However, the viral protein is only detected in approximately 30%-50% of NPC samples, as such its role in carcinogenesis and tumour maintenance can be questioned and thus its relevance as a therapeutic target.

RESULTS

In order to explore if LMP1 has a continuous function in established tumours, its activity was inhibited through expression of a dominant negative LMP1 mutant in tumour cell lines derived from transgenic mice. LMP1 is the tumour predisposing oncogene in two different series of transgenic mice which separately give rise to either B-cell lymphomas or carcinomas. Inhibition of LMP1 activity in the carcinoma cell lines lead to a reduction in clonagenicity and clone viability in all of the cell lines tested, even those with low or below detection levels of LMP1. Inhibition of LMP1 activity in the transgenic B-cell lines was incompatible with growth and survival of the cells and no clones expressing the dominant negative LMP1 mutant could be established.

CONCLUSIONS

LMP1 continues to provide a tumour cell growth function in cell lines established from LMP1 transgenic mouse tumours, of both B-cell and epithelial cell origin. LMP1 can perform this function, even when expressed at such low levels as to be undetectable, whereby evidence of its expression can only be inferred by its inhibition being detrimental to the growth of the cell. This raises the possibility that LMP1 still performs a pro-oncogenic function in the 50% to 70% of NPC tumours wherein LMP1 protein expression cannot be detected. This reinforces the basis for pursuing LMP1 as a therapeutic target in EBV associated LMP1-expressing malignancies.

Expression of Epstein-Barr virus latent membrane proteins leads to changes in keratinocyte cell adhesion

Epstein-Barr virus (EBV) has 3 latent membrane proteins (LMPs)--LMP1, LMP2a, and LMP2b--which are expressed in nasopharyngeal carcinoma. Using keratinocyte cell lines expressing LMP2a and LMP2b and coexpressing LMP1/LMP2a, we grew organotypic raft cultures to analyze changes in morphology and expression of the cell adhesion molecule ICAM-1; alpha2, alpha3, alpha5, beta1, and alpha6beta4 integrins; laminin 5; E-cadherin; and desmoplakin. Cells expressing LMP2a or LMP2b were defective in their ability to mature and progress through normal squamous stratification when compared to the parental cell lines. Cells coexpressing LMP1/LMP2a additionally demonstrated "pseudoinvasion" into the raft dermal equivalent. There was a consistent and dramatic up-regulation in the suprabasal expression of laminin 5 and alpha6beta4 and beta1 integrins in the LMP-expressing cell lines. ICAM-1, not expressed in the control cell lines, was up-regulated in the LMP-expressing cell lines. Expression of alpha3 and alpha5 integrins was also up-regulated in the LMP-expressing cell lines, while alpha2 demonstrated a loss of the normal basal layer expression. E-cadherin and desmoplakin expression patterns were essentially unchanged. We conclude that LMP2a and LMP2b singly, and LMP1/LMP2a coexpressed, are capable of altering keratinocyte cell adhesion molecule expression consistent with nasopharyngeal carcinoma.

Circulating intercellular adhesion molecule-1 and its cellular expression in head and neck non-Hodgkin's lymphomas, including lethal midline granuloma

Extranodal non-Hodgkin's lymphoma in the head and neck, especially T-cell lymphoma of the lethal midline granuloma (LMG) type, has unique clinical and histologic features differentiating it from other lymphomas. The authors measured soluble intercellular adhesion molecule-1 (ICAM-1) in sera from 12 patients with T-cell lymphoma of the LMG type and from 52 patients with other head and neck non-Hodgkin's lymphomas, by double-determinant immunoassay. The expression of ICAM-1 in lymphoma tissue was examined in 26 patients by the avidin-biotin immunoperoxidase method. The serum ICAM-1 levels were significantly higher in T-cell lymphoma of the LMG type than in other head and neck lymphomas or in healthy adult controls. Elevated levels of serum ICAM-1 were associated with increased levels of serum lactate dehydrogenase, poor prognosis, and impaired T-cell-dependent immune functions, both in T-cell lymphoma of the LMG type and in other head and neck lymphomas. When we monitored serum ICAM-1 levels in individual patients, the level decreased in the complete remission interval compared to before treatment and went up again when the lymphoma relapsed. Although the staining intensities of ICAM-1 in lymphoma cells were not related to serum ICAM-1 levels, a markedly intense expression of ICAM-1 was found on the angiocentric or angiodestructive lymphoreticular infiltrate region in the tissues from T-cell lymphoma of the LMG type. A higher serum ICAM-1 level and its tissue expression in T-cell lymphoma of the LMG type may be one of the clues to understanding this particular lymphoma. The serum ICAM-1 level could be an efficient parameter for monitoring the clinical course of head and neck non-Hodgkin's lymphomas.

Characteristic clinicopathologic features of Epstein-Barr virus-associated peripheral T-cell lymphoma

BACKGROUND

The authors previously reported the existence of a unique subtype of peripheral T-cell lymphoma (PTCL) characterized by a clonotypical proliferation of Epstein-Barr virus (EBV) in the tumor cells (Blood 1991; 77:799). Detailed clinicopathologic features of this newly recognized entity remain to be clarified.

METHODS

A retrospective study was done in 23 patients receiving consecutive diagnoses at National Taiwan University Hospital by methods previously described.

RESULTS

There were 13 male and 10 female patients, with a median age of 40 years. Seventeen patients had Stage III/IV disease, and 15 patients had fever as a presenting B symptom. Initial extranodal involvement occurred in skin (10 patients), lung (4 patients), bone marrow (4 patients), brain (3 patients), and nasal cavity (1 patient) and was evidenced by hepatosplenomegaly (6 patients). Sixteen patients had specific histopathologic features including characteristics similar to angioimmunoblastic lymphadenopathy with dysproteinemia (3 patients), angioinvasive-type features (6 patients), Hodgkin disease-like features (2 patients), hepatosinusoidal-type features (2 patients), Lennert lymphoma (2 patients), and malignant histiocytosis-like features (1 patient). Six (37.5%) of the 16 patients who received a standard regimen with cyclophosphamide, doxorubicin, vincristine, and prednisone or an equivalent regimen as induction chemotherapy achieved complete remission. The median survival time was only 8 months. Six (42.8%) of the 14 patients who have died at this report ended up with a terminal hemophagocytosis syndrome. All five relapsed tumors were found to have a strong expression of P-glycoprotein (P-gp).

CONCLUSIONS

The authors suggest that EBV-associated PTCL should be regarded as a separate entity of non-Hodgkin lymphoma showing characteristic histopathologic features, frequent expression of P-gp in relapsed tumor, a terminal hemophagocytosis syndrome, and a generally ominous outcome.