An immunohistochemical study of p53 protein expression in classical Kaposi's sarcoma

Kaposi's sarcoma-associated herpesvirus K-cyclin interacts with Cdk9 and stimulates Cdk9-mediated phosphorylation of p53 tumor suppressor

K-cyclin, encoded by Kaposi's sarcoma-associated herpesvirus, has previously been demonstrated to activate cyclin-dependent kinase 6 (Cdk6) to induce the phosphorylation of various cell cycle regulators. In this study, we identified Cdk9 as a new K-cyclin-associated Cdk and showed that K-cyclin interacted with Cdk9 through its basic domain. We hypothesized that K-cyclin served as a regulatory subunit for the activity of Cdk9. Recent reports show that Cdk9 phosphorylates tumor suppressor p53, and we found that the K-cyclin/Cdk9 interaction greatly enhanced the kinase activity of Cdk9 toward p53. The phosphorylation site(s) of K-cyclin/Cdk9 kinase complexes was mapped in the transactivation domain of p53. We showed that the ectopic expression of K-cyclin led to a sustained increase of p53 phosphorylation on Ser(33) in vivo, and the phosphorylation could be inhibited by a dominant negative Cdk9 mutant, dn-Cdk9. Using p53-positive U2OS and p53-null SaOS2 cells, we demonstrated that K-cyclin-induced growth arrest was associated with the presence of p53. In addition, K-cyclin-induced p53-dependent growth arrest was rescued by the dn-Cdk9- or Cdk9-specific short hairpin RNA in SaOS2 cells. Together, our findings for the first time demonstrated the interaction of K-cyclin and Cdk9 and revealed a new molecular link between K-cyclin and p53.

γ-Herpesvirus neoplasia: A growing role for COX-2

Both human gamma-herpesviruses, Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV) induce neoplasia. Burkitt's and Hodgkin's lymphomas harbor EBV sequences, while KSHV has been associated with Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and multicentric castleman's disease (MCD). Each of these gamma-herpesvirus-associated malignancies displays typical characteristics of neoplasia, such as angiogenesis and cell survival. One enzyme commonly overexpressed in breast, prostate, and colon cancers is cyclooxygenase-2 (COX-2). Recently, COX-2 overexpression has been reported in herpesvirus infections in vitro. This review will outline potential mechanisms by which COX-2 may participate in herpesvirus-induced neoplasia.

The role of p53 in suppression of KSHV cyclin-induced lymphomagenesis

Kaposi's sarcoma-associated herpesvirus (KSHV) encodes a cyclin D homolog, K cyclin, that is thought to promote viral oncogenesis. However, expression of K cyclin in cultured cells not only triggers cell cycle progression but also engages the p53 tumor suppressor pathway, which probably restricts the oncogenic potential of K cyclin. Therefore, to assess the tumorigenic properties of K cyclin in vivo, we transgenically targeted expression of K cyclin to the B and T lymphocyte compartments via the E micro promoter/enhancer. Around 17% of E micro -K cyclin animals develop lymphoma by 9 months of age, and all such lymphomas exhibit loss of p53. A critical role of p53 in suppressing K cyclin-induced lymphomagenesis was confirmed by the greatly accelerated onset of B and T lymphomagenesis in all E micro -K cyclin/p53(-/-) mice. However, absence of p53 did not appear to accelerate K cyclin-induced lymphomagenesis by averting apoptosis: E micro -K cyclin/p53(-/-) end-stage lymphomas contained abundant apoptotic cells, and transgenic E micro -K cyclin/p53(-/-) lymphocytes in vitro were not measurably protected from DNA damage-induced apoptosis compared with E micro -K cyclin/p53(wt) cells. Notably, whereas aneuploidy was frequently evident in pre-lymphomatous tissues, end-stage E micro -K cyclin/p53(-/-) tumors showed a near-diploid DNA content with no aberrant centrosome numbers. Nonetheless, such tumor cells did harbor more restricted genomic alterations, such as single-copy chromosome losses or gains or high-level amplifications. Together, our data support a model in which K cyclin-induced genome instability arises early in the pre-tumorigenic lymphocyte population and that loss of p53 licenses subsequent expansion of tumorigenic clones.

Angiogenic effects of extracellular human immunodeficiency virus type 1 Tat protein and its role in the pathogenesis of AIDS-associated Kaposi's sarcoma

The Tat protein of human immunodeficiency virus (HIV) type 1 is a transactivator of viral gene expression that is required for virus replication and spread. Moreover, Tat is released by acutely HIV-infected cells via a leaderless secretory pathway and in a biologically active form that exerts effects on both HIV-infected and uninfected cells from different organs and systems. This review focuses on the activities of extracellular Tat protein on endothelial cells, on angiogenesis, and on the pathogenesis of AIDS-associated angioproliferative diseases such as Kaposi's sarcoma. In particular, we discuss results from different groups indicating that Tat mimics the proangiogenic activities of extracellular matrix molecules and that it enhances the effects of angiogenic factors.

Expression of p53 and human herpesvirus-8 (HHV-8)-encoded latency-associated nuclear antigen with inhibition of apoptosis in HHV-8-associated malignancies

BACKGROUND

Kaposi sarcoma (KS) and primary effusion lymphoma (PEL) cells express human herpesvirus-8 (HHV-8)-encoded latency-associated nuclear antigen (LANA) (open reading frame [ORF] 73 protein), suggesting that LANA plays an important role in the pathogenesis of HHV-8-associated malignancies. Recently, the binding of LANA to p53 was demonstrated in vitro. In the current study, the authors investigated the association between p53 and LANA expression with apoptosis in HHV-8-associated malignancies in vivo.

METHODS

Twenty-six cases of KS, 1 case of HHV-8-associated solid lymphoma, 2 PEL cell lines, and an HHV-8-associated lymphoma engrafted in severe combined immunodeficiency (SCID) mice were examined. Immunohistochemistry using the catalyzed signal amplification system was employed to detect LANA and p53 on paraffin embedded tissues and the immunofluorescence technique was used on cell lines. To detect apoptosis, the TdT-mediated dUTP nick end labeling (TUNEL) method was used. For mutation analysis of p53, exons 5-9 of the p53 gene were amplified by polymerase chain reaction and examined by direct sequencing.

RESULTS

Immunohistochemistry revealed that LANA and p53 were expressed in the tumor cells of all these specimens, and apoptotic cells were rarely detected in them using the TUNEL method. Immunofluorescence assay revealed that LANA colocalized with p53 in the nuclei of PEL cells. Sequencing analysis indicated that there was no mutation in the deduced amino acid sequences of p53 in KS tissues.

CONCLUSIONS

These data suggest colocalization of p53 and LANA and the inhibition of apoptosis in HHV-8-associated malignancies in vivo, supporting the results found in vitro that p53 inhibition by LANA suppresses cell death, as reported previously. These results also suggest that the p53 pathway is crucial in the pathogenesis of HHV-8-associated malignancies.

Proliferation and apoptosis in the evolution of endemic and acquired immunodeficiency syndrome-related Kaposi's sarcoma

Kaposi's sarcoma (KS) is a multifocal lesion that occurs predominantly in the skin, most frequently in people infected with HIV-1, and that evolves through early stages (patch and plaque) to a tumor-like late stage (nodular). Both, endemic African (EKS) and AIDS-associated (AKS) KS expressed human herpesvirus 8 (HHV-8) as shown by PCR. By immunohistochemistry the expression of cellular Bcl-2 and c-myc was confined in early stages of both EKS and AKS to relatively few endothelial cells (EC) whereas in nodular KS most of spindle cells (SC) strongly expressed both genes. CD40 was usually strongly expressed in SC at all KS stages as well as in EC of non-involved tissue whereas CD40L (CD154) was not demonstrable. Fas (CD95) was moderately to weakly expressed by SC whereas p53 and Waf-1 were found in less than 5% of the SC. In both AKS and EKS at nodular stage almost no apoptotic SC were detected. In most AKS and EKS low levels of cell proliferation were seen but AKS showed consistently higher values compared to EKS. All clinical types and stages of KS showed a diploid cellular DNA content by flow cytometric analysis of microselected lesions. Thus, we conclude that KS during evolution represents diploid, probably reactive, cell proliferation, which progressively increases the expression of strong cellular and also viral (HHV-8) antiapoptotic factors.

Differential expression of p53 and Ki-67 proteins in classic and iatrogenic Kaposi's sarcoma

In many neoplasms, the finding p53 immunoreactivity correlates with striking cytologic atypia, a high tumor cell proliferation rate, and poor prognosis. The literature regarding p53 and Ki-67 (a nuclear proliferation-associated antigen) immunoreactivity in Kaposi's sarcoma is limited. We aimed to: (1) evaluate the role of p53 in the development of Kaposi's sarcoma; (2) determine whether there is a correlation between p53 and Ki-67 protein expression; and (3) determine possible differences between classical Kaposi's sarcoma, known usually to have a benign course, and iatrogenic Kaposi's sarcoma, the course of which is unpredictable, by studying the differential expression of p53 and Ki-67. Among 26 cases of classic KS and 19 of iatrogenic KS, 12 were classified histopathologically as early type and 33 as mixed or spindle-cell type. P53 and Ki-67 immunoreactivity correlated significantly with the histopathologic stage of KS (r=0.63, p=0.0001; r=0.42, p=0.0084, respectively). P53 was not detected in any of the cases in an early histopathologic stage but was present in 55% of the cases in a more advanced stage. The spindle cells increased in proportion with the histopathologic progression and were more often positive (p=0.019) and displayed more extensive staining than the endothelial cells (p=0.0001). There was a strong positive correlation between p53 and Ki-67 protein expression (r=0.43, p=0.0087). There was no correlation between the expression of either p53 or Ki-67 and the extent of the eruption. The expression of p53 and Ki-67 was significantly lower in iatrogenic cases than in the classic cases (p=0.009, p=0.0014, respectively), although no statistical difference was found between the histopathologic stages in the two clinical forms of KS. P53 immunoreactivity was detected in 79% of the cases of classic Kaposi's sarcoma in the mixed or spindle cell stage but in only 21.5% of the iatrogenic cases showing the same histopathologic stage (p=0.001), and the percentage of spindle cells as well as the endothelial cells expressing p53 was higher in the classic cases than in the iatrogenic cases (p=0.0032, p=0.0142, respectively). We conclude that p53 immunoexpression is a marker of tumor progression in classic Kaposi's sarcoma but not in most cases of iatrogenic Kaposi's sarcoma. The proliferative activity of the tumor cells in classic Kaposi's sarcoma is much higher than in iatrogenic Kaposi's sarcoma. Our work implies that the molecular steps involved in classic and iatrogenic Kaposi's sarcoma differ.

Bcl-2 and p53 immunoprofile in Kaposi's sarcoma

Seventy three cases of Kaposi's sarcoma (KS) from the 3 histological subtypes (patch, plaque and nodular) were assessed for bcl-2 and p53 protein expression. The aim was to determine the level of expression of these proteins in KS and in the different subtypes. Commercially available antibodies to bcl-2 and p53 were applied after both microwave and pressure cooking antigen retrieval. Bcl-2 immunoexpression increased from the patch stage (36%) to the plaque stage (45%) to the nodular stage (70.83%). Better immunostaining for bcl-2 was obtained after pressure cooking. p53 on the other hand, was not expressed in the patch or plaque stages, but 54.16% of cases in the nodular stage were immunopositive. These results show a progression of immunoexpression of both bcl-2 and p53 from the early histological stages to the late tumor stage, implying that these proteins are upregulated late in the evolution of KS.

Early- and late-stage Kaposi's sarcoma lesions exhibit similar proliferation fraction

There are few studies on the proliferative activity of cells in Kaposi's sarcoma. It remains unclear whether the different progressive histologic stages of Kaposi's sarcoma correlate with the proliferative activity of the tumor. To clarify this issue, we studied the Ki-67 proliferation index in 40 specimens of acquired immune deficiency syndrome-related Kaposi's sarcoma in correlation with the histologic stage of the lesions. The mean proliferation index in our combined material was rather low (8%, range 1-20%) and there was no significant difference among the different stages of the disease. Contrary to a common and probably misleading concept, our results suggest that the histologic progression of the Kaposi's sarcoma is not related to an increase of the proliferative compartment.

Human herpes virus 8 (HHV-8) in Kaposi's sarcoma: lack of association with Bcl-2 and p53 protein expression

AIMS

Human herpes virus 8 (HHV-8) is the infectious agent implicated in the pathogenesis of Kaposi's sarcoma, although its mode of action is unclear. Recent work indicates that the HHV-8 genome encodes a viral Bcl-2 homologue (v-Bcl-2). The aim of this study was to explore Bcl-2 expression in Kaposi's sarcoma using a unique set of HHV-8 positive and negative cases, and to determine whether there is a relation with p53 expression.

METHODS

Up to 18 specimens from 17 patients were selected. HHV-8 status was determined using nested polymerase chain reaction (PCR) to the open reading frame (ORF) 26, with further confirmation by TaqMan PCR. In addition, Bcl-2 and p53 immunohistochemistry were performed using standard protocols.

RESULTS

The results suggest that Bcl-2 and p53 expression is independent of HHV-8 status. In addition, there does not appear to be a direct correlation with disease stage.

CONCLUSIONS

HHV8 histopathogenesis is likely to be a multifactorial complex process, which may be mediated in part by viral genes and apoptosis regulating homologues.

Kaposi's sarcoma: a result of the interplay among inflammatory cytokines, angiogenic factors and viral agents

Kaposi's sarcoma (KS) is an angioproliferative disease occurring in 4 clinic-epidemiologic forms. Although the AIDS-associated KS (AIDS-KS) is the most aggressive, all forms of KS share the same immunological and histopathological features suggesting common etiological and pathogenic factors. Recent data indicate that at least in early stage KS is not a real sarcoma but an angiohyperplastic-inflammatory lesion mediated by inflammatory cytokines and angiogenic factors, that is triggered or amplified by infection with human herpesvirus-8. In addition, the human immunodeficiency virus type-1 Tat protein appears to be responsible for the higher grade of aggressiveness of AIDS-KS as compared to the other forms of KS. However, given time, reactive KS may progress to a sarcoma as suggested by evidence of monoclonality in late-nodular lesions.