Functional analysis of the p53 protein in AIDS-related non-Hodgkin's lymphomas and polymorphic lymphoproliferations

Overexpression of microRNAs from the miR-17-92 paralog clusters in AIDS-related non-Hodgkin's lymphomas

BACKGROUND

Individuals infected by HIV are at an increased risk for developing non-Hodgkin's lymphomas (AIDS-NHL). In the highly active antiretroviral therapy (HAART) era, there has been a significant decline in the incidence of AIDS-associated primary central nervous system lymphoma (PCNSL). However, only a modest decrease in incidence has been reported for other AIDS-NHL subtypes. Thus, AIDS-NHLs remain a significant cause of morbidity and mortality in HIV infected individuals. Recently, much attention has been directed toward the role of miRNAs in cancer, including NHL. Several miRNAs, including those encoded by the miR-17-92 polycistron, have been shown to play significant roles in B cell tumorigenesis. However, the role of miRNAs in NHL in the setting of HIV infection has not been defined.

METHODOLOGY/PRINCIPAL FINDINGS

We used quantitative realtime PCR to assess the expression of miRNAs from three different paralog clusters, miR-17-92, miR-106a-363, and miR-106b-25 in 24 cases of AIDS-NHLs representing four tumor types, Burkitt's lymphoma (BL, n = 6), diffuse large B-cell lymphoma (DLBCL, n = 8), primary central nervous system lymphoma (PCNSL, n = 5), and primary effusion lymphoma (PEL, n = 5). We also used microarray analysis to identify a differentiation specific miRNA signature of naïve, germinal center, and memory B cell subsets from tonsils (n = 4). miRNAs from the miR-17-92 paralog clusters were upregulated by B cells, specifically during the GC differentiation stage. We also found overexpression of these miRNA clusters in all four AIDS-NHL subtypes. Finally, we also show that select miRNAs from these clusters (miR-17, miR-106a, and miR-106b) inhibited p21 in AIDS-BL and DLBCL cases, thus providing a mechanistic role for these miRNAs in AIDS-NHL pathogenesis.

CONCLUSION

Dysregulation of miR-17-92 paralog clusters is a common feature of AIDS-associated NHLs.

A case of HIV-associated lymphoproliferative disease that was successfully treated with highly active antiretroviral therapy

We report a case of a 41-year-old male with human immunodeficiency virus (HIV)-associated lymphoproliferative disease (LPD) who was successfully treated with highly active antiretroviral therapy (HAART). He presented with epigastralgia, and an upper endoscopic examination revealed submucosal tumors and ulcerations in his stomach. Histopathologic examination of a biopsy specimen resulted in a diagnosis of diffuse large B-cell lymphoma. He also showed systemic lymphadenopathy; whereas, a concurrent inguinal lymph node biopsy produced a diagnosis of follicular hyperplasia. He was treated with CHOP chemotherapy but the response was poor. He demonstrated several immunological abnormalities, such as eosinophilia and bone marrow insufficiency, and was suspected to be in an immunocompromised state. He was examined for HIV infection and turned out to be positive. The gastric and inguinal lymph node specimens were re-evaluated and diagnoses of HIV-LPD and HIV lymphadenitis were made, respectively. He was treated with HAART and achieved complete remission and has remained tumor-free for 20 months. To the best of our knowledge, there is no previous report in which HIV-LPD was successfully treated with antiretroviral therapy alone. It is assumed that HAART resulted in the restoration of anti-tumor immunity in this case, which led to the eradication of LPD cells.

Atypical hyperplasia of the marginal zone of B follicles in a polymorphic Epstein-Barr virus-associated lymphoproliferative disorder occurring in an adolescent with human immunodeficiency virus infection

Epstein-Barr virus (EBV)-associated lymphoid proliferations that are similar to post-transplantation lymphoproliferative disorders may occasionally occur in the setting of human immunodeficiency virus (HIV) infection. Herein, we describe such a lesion involving the adenoids in a HIV-seropositive adolescent who acquired immunity against EBV during childhood. On microscopic examination, the marginal zone of B follicles and the interfollicular area were enlarged due to the accumulation of small or intermediate-sized lymphocytes, immunoblasts, epithelioid histiocytes, and plasma cells. A few atypical immunoblasts resembling Reed-Sternberg cells were also present. Most of the cells seen in these expanded regions belonged to the B-cell lineage and displayed a phenotype consistent with that of postgerminal center B cells. No clonal rearrangement of the genes coding for the heavy chain of the immunoglobulin could be demonstrated by polymerase chain reaction analysis. In-situ hybridization studies revealed the presence of EBV early RNA in a significant number of these cells, which suggests the participation of this virus in the pathogenesis of such a B-cell proliferation. The clinical course was benign; no progression or recurrence could be seen more than 24 months after the diagnosis. This atypical lymphoproliferative disorder is probably related to polyclonal reactivation of a latent EBV infection due to a local or systemic immune imbalance induced by HIV replication. Recognition of this reactive condition is important to prevent overtreatment.

Mechanisms involved in Burkitt's tumor formation

Burkitt's lymphoma is a rapidly fatal tumor if untreated, but it is curable with intensive polychemotherapy. Unfortunately, the toxicities reported for its treatment in adults are poorly tolerated. Novel therapies aimed at specific molecular targets might prove to be less toxic. A better knowledge of the mechanisms involved in the pathogenesis of Burkitt's lymphoma would facilitate the identification of such targets. This review explores the current knowledge on the alterations found in the three main Burkitt's lymphoma variants.

Genomic imbalances in AIDS-related lymphomas: relation with tumoral Epstein-Barr virus status

BACKGROUND

The pathologic heterogeneity of AIDS related lymphomas (ARL) reflects several pathogenic mechanisms: chronic antigenic stimulation, Epstein-Barr virus (EBV) infection, and genomic abnormalities. Genetic abnormalities, known to play a major role in lymphomas of non-immunocompromised patients, are not well characterized in ARL.

OBJECTIVE

Characterization of the DNA copy number change (CNC) in ARL and comparison of our findings with tumoral EBV and immune status.

DESIGN AND METHODS

We have studied by comparative genomic hybridization (CGH), 28 ARL well characterized for histopathologic, clonality and EBV findings.

RESULTS

DNA-CNC were detected in 50% of cases. Gains of chromosomal material were much more frequent than losses and involved chromosomes 9p, 11q, 12q, 17q, and 19q recurrently. DNA-CNC tended to be more frequent in EBV-positive lymphomas with latency type II/III than in EBV-positive latency I or EBV-negative lymphomas. Most chromosomal regions affected in HIV-related lymphoma were similar to those already reported in HIV-negative lymphomas.

CONCLUSION

This CGH study allowed the identification of non-random chromosomal alterations in ARL. The results suggested an inverse relationship between EBV infection (latency II/III), associated with deep acquired immune suppression, and the number of chromosomal alterations which may be explained by a direct role of viral proteins in lymphomagenesis by activation of signalling pathways without needing several genomic alterations.

Plasmablastic lymphoma presenting in a human immunodeficiency virus-negative patient: a case report

Plasmablastic lymphoma (PBL), an aggressive non-Hodgkin's lymphoma that carries a poor prognosis, previously has been identified almost exclusively in patients infected with the human immunodeficiency virus (HIV). We present a case of a 42-year-old HIV-negative patient presenting with an isolated nasal cavity mass, the typical presentation for PBL. The patient was given systemic chemotherapy, central nervous system prophylaxis, and consolidative locoregional radiotherapy and achieved a complete clinical response. This case suggests PBL should be considered in HIV-negative patients with characteristic findings.

Highly effective treatment of acquired immunodeficiency syndrome-related lymphoma with dose-adjusted EPOCH: impact of antiretroviral therapy suspension and tumor biology

The outcome of acquired immunodeficiency syndrome-related lymphomas (ARLs) has improved since the era of highly active antiretroviral therapy, but median survival remains low. We studied dose-adjusted EPOCH (etoposide, prednisone, vincristine, cyclophosphamide, and doxorubicin) with suspension of antiretroviral therapy in 39 newly diagnosed ARLs and examined protein expression profiles associated with drug resistance and histogenesis, patient immunity, and HIV dynamics and mutations. The expression profiles from a subset of ARL cases were also compared with a matched group of similarly treated HIV-negative cases. Complete remission was achieved in 74% of patients, and at 53 months median follow-up, disease-free and overall survival are 92% and 60%, respectively. Following reinstitution of antiretroviral therapy after chemotherapy, the CD4+ cells recovered by 12 months and the viral loads decreased below baseline by 3 months. Compared with HIV-negative cases, the ARL cases had lower bcl-2 and higher CD10 expression, consistent with a germinal center origin and good prognosis, but were more likely to be highly proliferative and to express p53, adverse features with standard chemotherapy. Unlike HIV-negative cases, p53 overexpression was not associated with a poor outcome, suggesting different pathogenesis. High tumor proliferation did not correlate with poor outcome and may partially explain the high activity of dose-adjusted EPOCH. The results suggest that the improved immune function associated with highly active antiretroviral therapy (HAART) may have led to a shift in pathogenesis away from lymphomas of post-germinal center origin, which have a poor prognosis. These results suggest that tumor pathogenesis is responsible for the improved outcome of ARLs in the era of HAART.

Update on the Pathogenesis, Diagnosis, and Therapy of AIDS-related Lymphoma

AIDS-related non-Hodgkin's lymphoma (ARL) is an opportunistic malignancy that foreshortens life more than any other commonly occurring HIV-associated cancer. Treatment strategies include low-dose chemotherapy, chemotherapy given with antiretroviral therapy, and infusional chemotherapy regimens. Rituximab, an anti-CD20 monoclonal antibody, has been found to be useful in non-HIV-associated lymphomas and is of interest in ARL as well. Since the advent of highly active antiretroviral therapy, the ARL incidence and survival has changed. This paper reviews the epidemiologic, biologic, and clinical features of ARL with the aim of presenting a cohesive overview of these elements.

TP53 in hematological cancer: low incidence of mutations with significant clinical relevance

Inactivation of the wild-type p53 gene (TP53) by various genetic alterations is a major event in human tumorigenesis. More than 60% of human primary tumors exhibit a mutation in the p53 gene. Hematological malignancies present a rather low incidence of genetic alterations in this gene (10-20%). Nevertheless, epidemiological studies of the hematological malignancies indicate that the prognosis of patients with a mutation in the p53 gene is worse than those expressing the wild-type p53 protein. Correlations between drug resistance, altered apoptosis, and mutations in the p53 gene are found in hematological malignancies and leukemias. These issues, as well as the possibility of exploiting p53 and its various functions for new therapeutic strategies, are discussed in the present review.

Emerging pathways in the development of AIDS-related lymphomas

The clinicopathological range of AIDS-related non-Hodgkin lymphomas (NHLs) includes systemic lymphomas, primary central-nervous-system lymphomas, primary effusion lymphoma, and plasmablastic lymphoma of the oral cavity. Most AIDS-related NHLs belong to one of three categories of high-grade B-cell lymphomas: Burkitt's lymphoma, centroblastic lymphoma, and immunoblastic lymphoma. The pathological heterogeneity of AIDS-related NHL reflects the heterogeneity of their associated molecular lesions. In AIDS-related Burkitt's lymphoma, the molecular lesions involve activation of c-MYC, inactivation of p53, and infection with Epstein-Barr virus (EBV). AIDS-related immunoblastic lymphomas infected with EBV are characterised by frequent expression of latent membrane protein 1-an EBV oncoprotein. The biological heterogeneity of AIDS-related NHLs is highlighted by their histogenetic differences; AIDS-related NHLs are related to distinct B-cell subgroups (eg, germinal-centre or post-germinal-centre B cells). The phenotypic pattern of AIDS-related Burkitt's lymphomas and systemic AIDS-related centroblastic lymphomas closely reflects that of B cells in germinal centres. Conversely, the phenotype of AIDS-related immunoblastic lymphomas and AIDS-related primary effusion lymphomas reflects post-germinal-centre B cells in all cases. Despite their clinicopathological, genetic, and phenotypic heterogeneity, most lymphomas in patients with AIDS carry somatic mutations of immunoglobulin and BCL-6 genes. However, the somatic hypermutation mechanism functions aberrantly in a significant proportion of AIDS-related NHLs, causing the mutation of many genes, and possibly favouring chromosomal translocation, which may be a powerful contributor to malignant transformation. New molecular and virological evidence of such pathways and a greater knowledge of other biological features of AIDS-related NHLs may lead to new targets for pathogenetically and biologically oriented therapies.

Application of a yeast assay to detect functional p53 mutations in archival prostate cancer tissue

Detection and functional evaluation of mutant p53 alleles using a yeast assay could yield significant information for predicting the prognosis of patients with prostate cancer (CaP). Since the current version of this yeast assay is not applicable to archival tissues, we developed a modified assay for use on formalin-fixed, paraffin-embedded tissue and have applied it to the study of patient samples. Using this modified assay, we examined archival CaP samples from 10 patients for mutations in exons 5-8 of p53 gene. Mutations were detected in four samples: three resulted in the formation of red yeast colonies indicating complete loss of function, while one gave pink yeast colonies, indicating that this mutant retained partial function. In parallel, we analyzed these samples for p53 abnormalities using a single-strand conformational polymorphism (SSCP) approach. Only three of the four yeast-positive samples gave abnormal SSCP bands. In each case where abnormal p53 was found by both methods, DNA sequencing revealed the identical base change. These results suggest that the modified yeast assay may be more sensitive than SSCP for detection of p53 mutations, and demonstrate that the modified method can be used to detect and evaluate the function of p53 mutants present in archival tissue.

Tumor suppressor genes in normal and malignant hematopoiesis

Over the last decade, a growing number of tumor suppressor genes have been discovered to play a role in tumorigenesis. Mutations of p53 have been found in hematological malignant diseases, but the frequency of these alterations is much lower than in solid tumors. These mutations occur especially as hematopoietic abnormalities become more malignant such as going from the chronic phase to the blast crisis of chronic myeloid leukemia. A broad spectrum of tumor suppressor gene alterations do occur in hematological malignancies, especially structural alterations of p15(INK4A), p15(INK4B) and p14(ARF) in acute lymphoblastic leukemia as well as methylation of these genes in several myeloproliferative disorders. Tumor suppressor genes are altered via different mechanisms, including deletions and point mutations, which may result in an inactive or dominant negative protein. Methylation of the promoter of the tumor suppressor gene can blunt its expression. Chimeric proteins formed by chromosomal translocations (i.e. AML1-ETO, PML-RARalpha, PLZF-RARalpha) can produce a dominant negative transcription factor that can decrease expression of tumor suppressor genes. This review provides an overview of the current knowledge about the involvement of tumor suppressor genes in hematopoietic malignancies including those involved in cell cycle control, apoptosis and transcriptional control.

Expression of p16/INK4a in posttransplantation lymphoproliferative disorders

It was recently demonstrated that classification of posttransplantation lymphoproliferative disorders (PT-LPDs) into morphological and molecular categories is clinically relevant. It was also reported that PT-LPD not associated with Epstein-Barr virus (EBV) had a more aggressive course than most lesions associated with EBV. Because the cyclin-dependent kinase inhibitor p16/INK4a has been reported to be frequently inactivated in high-grade lymphomas, we evaluated 17 PT-LPD to determine whether p16/INK4a expression could be correlated to morphology, EBV detection, and a Ki-67 labeling index. We demonstrated that tumors with no p16/INK4a expression (n = 8) had a predominantly monomorphic appearance, and most were EBV negative (respectively, 7/8 and 5/8), whereas lesions with p16/INK4a expression (n = 9) were mostly polymorphic PT-LPD (6/9) (P = 0.049) and associated with EBV (9/9) (P = 0.015). In particular, strong p16/INK4a expression was observed in atypical immunoblasts and Reed-Sternberg-like cells. Furthermore, the proliferation index was significantly higher in tumors lacking p16/INK4a expression than in other lesions (P = 0.0008). In conclusion, down-regulation of p16/INK4a was mostly observed in PT-LPD lesions known to follow more aggressive courses: monomorphic tumors and EBV-negative PT-neoplasms. Conversely, overexpression of p16/INK4a was associated with EBV-positive PT-LPD. While p16/INK4a might play a role in the proliferative rate of LP-LPD, further investigations are needed to assess the clinical relevance of p16/INK4a expression in predicting the evolution of tumors and to explain how EBV could favor p16/INK4a protein accumulation in lesions.

Simian AIDS-associated lymphoma in rhesus and cynomolgus monkeys recapitulates the primary pathobiological features of AIDS-associated non-Hodgkin's lymphoma

Non-Hodgkin's lymphomas occur with increased frequency (3-6%) in HIV-infected individuals. These AIDS-associated lymphomas (AALs) exhibit characteristics that distinguish them from lymphomas in the general population. A proposed model for the pathogenesis of AAL includes the following: (1) Tumorigenesis is multistep; (2) tumors occur in long-term survivors; (3) tumors are of clonal B cell origin; (4) HIV acts early and is an indirect effector; (5) tumor cells are infected with EBV; and (6) specific genetic lesions occur in tumor cells. Many aspects of this process remain to be tested in an animal model system. Since 1984, necropsy examinations have been performed on more than 1000 SIV-infected rhesus and cynomolgus monkeys at the Tulane Regional Primate Research Center. Lymphoid malignancies were detected in a proportion of SIV-infected animals. These SAIDS-associated lymphomas (SALs) have been studied to determine the extent to which their pathological features recapitulate a working model for the pathogenesis of AAL. The results show that lymphomas occur in SIV-infected rhesus macaques at 4% incidence, similar to that of AAL, and that the incidence of SAL in cynomolgus macaques is eightfold higher. Analysis of SAL from both species of macaques demonstrated significant similarity to the hallmark pathobiological features of AAL. These findings indicate that the HIV-infected human and the SIV-infected macaque share a common pathobiology and mechanism of lymphomagenesis.

Use of a yeast assay to detect functional alterations in p53 in prostate cancer: review and future directions

BACKGROUND

While many studies have suggested that p53 mutations are common in human cancers, the functional activity of these mutant alleles has not yet been fully addressed. We believe that information about the functional status of individual p53 mutants will prove to be important for a better understanding of the role of p53 in tumor development and progression. Ultimately, this information could also influence treatment decisions for individual cancer patients.

METHODS

A recently developed yeast functional assay can be used to assess the transactivational activity of p53 mutants. Furthermore, this assay is more sensitive than single strand conformational polymorphism (SSCP) for detection of p53 mutations. In this review, we summarize the mechanism of this new technique and describe its applications in cancer research, with an emphasis on prostate cancer.

RESULTS

The use of the yeast functional assay provides a simple, sensitive, and reproducible method for detecting p53 mutations and for determining the transactivational activity and dominant-negative role of individual p53 mutants.

CONCLUSIONS

This method may be adapted to analyze other transcriptional factors, including the human androgen receptor.

High expression of MDM2 protein and low rate of p21(WAF1/CIP1) expression in SCID mice Epstein Barr virus-induced lymphoproliferation

To study the prevalence of p53 inactivation and MDM2/p21(WAFI/CIP1) expression in severe combined immunodeficient (SCID) mice Epstein-Barr virus (EBV)-induced lymphoproliferation, 19 samples obtained after ip injection of peripheral blood mononuclear cells (PBMCs) from EBV-seropositive donors or lymphoblastoid cell lines (LCL) were analyzed. In all samples tested, overexpression of Ki-67 antigen was shown by immunohistochemistry, indicating a high proliferative index of SCID mice EBV-induced lymphoproliferation. P53 mutations were screened by functional assay in yeast in 14 samples. With this test, a p53-inactivating mutation was found in only one case; the remaining cases exhibited a wild-type p53 pattern. However, an accumulation of p53 protein was detected by immunohistochemistry in six of 19 samples. P21 expression was found in seven of 19 samples but was not correlated with the rate of p53 protein in tumors. In contrast, high levels of nuclear accumulation of MDM2 were found in all samples by immunohistochemistry. These results suggest that a high Ki-67 proliferative index in SCID mice EBV-induced lymphoproliferation is not due to the inactivation of p53 by mutation, but could be associated with an overexpression of MDM2, which would act by a p53-independent mechanism.(J Histochem Cytochem 47:1315-1321, 1999)

MYC oncogenes and human neoplastic disease

c-myc, N-myc and L-myc are the three members of the myc oncoprotein family whose role in the pathogenesis of many human neoplastic diseases has received wide empirical support. In this review, we first summarize data, derived mainly from non-clinical studies, indicating that these oncoproteins actually serve quite different roles in vivo. This concept necessarily lies at the heart of the basis for the observation that the deregulated expression of each MYC gene is reproducibly associated with only certain naturally occurring malignancies in humans and that these genes are not interchangeable with respect to their aberrant functional consequences. We also review evidence implicating each of the above MYC genes in specific neoplastic diseases and have attempted to identify unresolved questions which deserve further basic or clinical investigation. We have made every attempt to review those diseases for which significant and confirmatory evidence, based on studies with primary tumor material, exists to implicate MYC members in their causation and/or progression.

Epstein-Barr virus and lymphoproliferative disease

The Epstein-Barr virus is a ubiquitous human herpesvirus that is associated with an increasing number of human malignancies. Among these are Epstein-Barr virus-associated lymphoproliferative diseases in immunocompromised patients, a spectrum of mainly B-cell diseases that range from polyclonal lymphoproliferative diseases, which resolve when immunosuppression is halted, to highly malignant lymphomas. Progress has identified Epstein-Barr virus gene products involved in B-cell transformation, variation in Epstein-Barr virus transforming genes, distinct target cell populations with differing regulation of Epstein-Barr virus expression, and selective recruitment of other supportive cell types as factors in the heterogeneity of lymphoproliferative diseases. New therapeutic approaches to treat lymphoproliferative diseases are also being developed. Finally, xenotransplantation poses new risks for the introduction of Epstein-Barr virus-like viruses and more aggressive lymphoproliferative diseases in heavily immunosuppressed patients.