Two domains within the adenovirus type 12 E1A unique spacer have disparate effects on the interaction of E1A with P105-Rb and the transformation of primary mouse cells

Interaction of Adenovirus E1A with the HHV8 Promoter of Latent Genes: E1A Proteins are Able to Activate the HHV-8 LANAp in MV3 Reporter Cells

Human herpesvirus 8 (HHV-8) is associated with Kaposi's sarcoma, body cavity-based lymphoma, and Castleman's disease. Adenoviral (Ad) E1A proteins regulate the activity of cellular and viral promoters/enhancers and transcription factors and can suppress tumorigenicity of human cancers. As (i) HHV-8 and Ad may co-exist in immunocompromised patients and (ii) E1A might be considered as therapeutic transgene for HHV-8-associated neoplasms we investigated whether the promoter of the latency-associated nuclear antigen (LANAp) controlling expression of vCyclin, vFLIP, and LANA proteins required for latent type infection is regulated by E1A. Transfection experiments in MV3 melanoma cells revealed activation of the LANAp by Ad5 E1A constructs containing an intact N terminus (aa 1-119). In particular, an Ad12 E1A mutant, Spm2, lacking six consecutive alanine residues in the "spacer" region activated the HHV-8 promoter about 15-fold compared to vector controls. In summary, we report the activation of the LANAp by E1A as a novel interaction of E1A with a viral promoter. These data may have relevance for the management of viral infections in immunocompromised patients. A role for E1A as a therapeutic in this context remains to be defined.

Rb2/p130 and protein phosphatase 2A: key mediators of ovarian carcinoma cell growth suppression by all-trans retinoic acid

Despite a number of attempts to improve treatment of ovarian cancer, it remains the most common cause of death from gynecological cancers. Thus, it is very important to identify more effective drugs for treatment and prevention of ovarian cancer. All-trans-retinoic acid (ATRA) has been shown to arrest the growth of ovarian carcinoma cells in G0/G1 and to significantly elevate levels of Rb2/p130 protein, a member of the retinoblastoma family of tumor suppressors. As ATRA treatment leads to a significant increase in the amount of Rb2/p130 protein but not mRNA, the elevated levels of Rb2/p130 protein is likely the result of increased stability. In studies to elucidate the mechanism by which ATRA alters Rb2/p130 stability in ovarian cancer cells, it was determined that PP2A, a serine/threonine phosphatase, binds and dephosphorylates Rb2/p130. Dephosphorylated Rb2/p130 exhibits decreased ubiquitination and thus is not degraded by the proteasome. The sites at which PP2A catalytic subunit (PP2Ac) interacts with Rb2/p130 have been localized to the NLS in the C-terminus of Rb2/p130. These sites are also involved in the interaction of Rb/p130 with importin beta and importin alpha, members of the nuclear transport machinery. It is known that importin alpha recognizes a NLS on a target protein and importin beta binds the nuclear pore complex. Moreover, it has been shown that the binding of importin alpha to NLS significantly decreases with phosphorylation of NLS. In ATRA-treated ovarian carcinoma cells, PP2A binds to Rb2/p130 and dephosphorylates the NLS of Rb2/p130 leading to the interaction of importin alpha with Rb2/p130. Importin beta then binds to the importin alpha-Rb2/p130 complex, leading to the translocation of the Rb2/p130 to the nucleus where it acts to arrest ovarian cancer cells in G1 and suppress proliferation.

E1A-Based Determinants of Oncogenicity in Human Adenovirus Groups A and C

A broad spectrum of genetic and molecular investigations carried out with group C, Ad2 and Ad5, and with group A, Ad12, have shown that early region1 (E1) gene products are sufficient for complete transformation of rodent cells in vitro by these viruses. During the past quarter century, the processes by which E1A proteins, in cooperation with E1B proteins, perturb the cell cycle and induce the transformed phenotype, have become well defined. Somewhat less understood is the basis for the differential oncogenicity of these two groups of viruses, and the processes by which the E1A proteins of Ad12 induce a tumorigenic phenotype in transformants resulting from infection of cells in vivo and in vitro. In this chapter we review previous findings and present new evidence which demonstrates that Ad12 E1A possesses two or more independent functions enabling it to induce tumors. One of these functions lies in its capacity to repress transcription of MHC class I genes, allowing the tumor cells to avoid lysis by cytotoxic T lymphocytes. We have shown that class I repression is mediated through increased binding of repressor COUP-TF and decreased binding of NF-kB to the class I enhancer. In addition to mediating immune escape, E1A also determines the susceptibility of transformants to Natural Killer (NK) cell lysis, and in this case, also, Ad12 transformants are not susceptible. By using Ad12 mutants containing chimeric E1A Ad12-Ad5 genes, point mutations, or a specific deletion, we have shown that the unique spacer region of Ad12 E1A is an oncogenic determinant, but is not required for transformation in vitro. Given that the E1A regions responsible for class I repression are first exon encoded, we have examined a set of cell lines transformed by these altered viruses, and have found that while they display greatly reduced tumorigenicity, they maintain a wildtype capacity to repress class I transcription. Whether the spacer contributes to NK evasion remains unresolved. Lastly, we discuss the properties of the Ad2/Ad5 E1A C-terminal negative modulator of tumorigenicity, and examine the effects on transformation, tumor induction and transformant tumorigenicity, when the Ad5 negative modulator is placed by chimeric construction in Ad12 E1A.

Tumor-specific activation of hTERT-derived promoters by tumor suppressive E1A-mutants involves recruitment of p300/CBP/HAT and suppression of HDAC-1 and defines a combined tumor targeting and suppression system

Adenovirus (Ad) E1A proteins are transcriptional regulators with antioncogenic but also transforming properties. We have previously shown that transformation-defective Ad5 E1A-derivatives are excellent tumor suppressors. For tumor-specific expression of the E1A-derivatives we intend to use tumor specific human telomerase reverse transcriptase (hTERT) core promoters. Here, we show that Spm2 and other E1A proteins with an intact amino terminus activated all hTERT constructs 10-20-fold in malignant tumor cells but not in primary fibroblasts, without affecting the activity of endogenous telomerase. The transcription rate in tumor cells was in the range of transcription from the SV40 promoter, which qualifies an E1A-hTERT system as a putative tumor targeting/expression system. The activation of the hTERT promoter by E1A was enhanced upon deletion of the Wilms' tumor 1 negative regulatory element and maintained high after deletion of the adjacent c-Myc-responsive E-box, demonstrating an important role of the remaining sequences that contain several Sp1-motifs. E1A-mediated hTERT activation was independent from the presence of the conserved region 3 (CR3) of E1A but dependent on E1A's binding to p300/CBP and recruitment of its histone acetyltransferase activity. Moreover, E1A-Spm2 and histone deacetylase-1 behaved as antagonists with respect to the regulation of transcription from the hTERT promoter. Overall, hTERT promoter/E1A-Spm2 systems may turn out to be excellent tools for transcriptionally targeted anticancer gene therapy.