The contribution of NF-kappa B activity to spontaneous proliferation and resistance to apoptosis in human T-cell leukemia virus type 1 Tax-induced tumors.

Human T-cell leukemia virus type I is the etiologic agent of adult T-cell leukemia/lymphoma. The Tax protein of this virus is thought to contribute to cellular transformation and tumor development. In this report, we have used a Tax transgenic mouse model of tumorigenesis to study the contribution of nuclear factor (NF)-kappa B activity to spontaneous tumor cell proliferation and resistance to apoptosis. We have demonstrated elevated expression levels of NF-kappa B--inducible cytokines, including interleukin (IL)-6, IL-10, IL-15, and interferon (IFN)-gamma, in freshly isolated primary tumors from Tax transgenic mice. Inhibitors of NF-kappa B activity, sodium salicylate and cyclopentenone prostaglandins (prostaglandin A(1) and 15-deoxy-Delta(12,14)-prostaglandin J(2)), blocked spontaneous proliferation of Tax transgenic mouse spleen cells. In addition, Tax-induced tumor cells, which are resistant to irradiation-induced apoptosis, became sensitive to apoptosis in the presence of sodium salicylate and prostaglandins. These results strongly suggest that Tax-mediated induction of NF-kappa B activity contributes to tumorigenesis in vivo. (Blood. 2001;98:1200-1208)

Analysis of p53 inactivation in a human T-cell leukemia virus type 1 Tax transgenic mouse model.

Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia/lymphoma (ATLL). The HTLV-1 Tax protein has been strongly linked to oncogenesis and is considered to be the transforming protein of this virus. A Tax transgenic mouse model was utilized to study the contribution of p53 inactivation to Tax-mediated tumorigenesis. These mice develop primary, peripheral tumors consisting of large granular lymphocytic (LGL) cells, which also infiltrate the lymph nodes, bone marrow, spleen, liver, and lungs. Primary Tax-induced tumors and tumor-derived cell lines exhibited functional inactivation of the p53 apoptotic pathway; such tumors and tumor cell lines were resistant to an apoptosis-inducing stimulus. In contrast, p53 mutations in tumors were found to be associated with secondary organ infiltration. Three of four identified mutations inhibited transactivation and apoptosis induction activities in vitro. Furthermore, experiments which involved mating Tax transgenic mice with p53-deficient mice demonstrated minimal acceleration in initial tumor formation, but significantly accelerated disease progression and death in mice heterozygous for p53. These studies suggest that functional inactivation of p53 by HTLV-1 Tax, whether by mutation or another mechanism, is not critical for initial tumor formation, but contributes to late-stage tumor progression.

Studies of the immortalizing activity of HTLV type 1 Tax, using an infectious molecular clone and transgenic mice.

Expression of Tax in the mature lymphoid compartment of transgenic mice resulted in a lymphoproliferative malignancy of natural killer cells and cytotoxic T lymphocytes. Transgenic mouse tumors exhibited mutations in the p53 tumor suppressor gene, and functional inactivation of wild-type p53 protein. Tax transgenic mice heterozygous for the p53 gene exhibited more rapid tumor dissemination and accelerated mortality. Studies of Tax trans-activation in an infectious clone of HTLV-1 demonstrated a critical role for nuclear factor B activation in lymphocyte immortalization. A mutant disrupting Tax activation of the cAMP response element binding (CREB) protein resulted in preferential immortalization of CD8(+) lymphocytes, rather than preferential immortalization of CD4(+) lymphocytes seen with the wild-type infectious clone. A mutation disrupting Tax interaction with CREB-binding protein, CBP, did not affect lymphocyte immortalization by the infectious molecular clone. These models provide new insights into the molecular details of HTLV-1 leukemogenesis.

Gene structure of human and mouse NKLAM, a gene associated with cellular cytotoxicity.

A novel gene involved in cytotoxicity, NKLAM [for "natural killer (NK) lytic-associated molecule"], has recently been identified in human NK cells. Its expression correlates with the cytolytic activity of both NK cells and cytotoxic T cells (CTLs); treatment of these cells with NKLAM-specific antisense oligonucleotides inhibits their cytotoxic function. NKLAM encodes a zinc finger protein that resides in NK cytolytic granules. Here, we identified a second human NKLAM transcript that differs from the original only at the 3' end, extending the open reading frame, and therefore encoding a significantly longer protein (731 residues compared with 587). The genomic structure of human NKLAM indicates that these two isoforms are products of alternative splicing. Both forms of NKLAM protein are expressed in NK cells, with the larger protein predominant. Human NKLAM cDNA was used to isolate mouse NKLAM from a C57BL/6 spleen cDNA library. There is a single NKLAM isoform in the mouse which shares over 89% nucleotide and 94% amino acid homology with the larger human form of NKLAM. The genomic organization of NKLAM is similar in both mouse and human. As with human NKLAM, mouse NKLAM mRNA is selectively expressed in CD8+ T cells NK cells, and activated peritoneal macrophages and further induced by cytokines that enhance the cytotoxic activity of these cells. These results indicate that human and mouse NKLAM are highly conserved both structurally and functionally, reinforcing the premise that this gene plays an important role in cellular cytotoxicity.

NK lytic-associated molecule: a novel gene selectively expressed in cells with cytolytic function.

NK cells are most effective in killing a broad spectrum of primary tumor cells after stimulation with cytokines. We have cloned a novel gene, designated NKLAM (for NK lytic-associated molecule), whose expression is associated with this cytokine-enhanced process. NKLAM expression is up-regulated in NK cells by IL-2 and IFN-beta. NKLAM is also selectively expressed by activated macrophages and CTL. Treatment of NK cells and CTL with NKLAM antisense oligonucleotides specifically decreases their cytolytic activity, while having no effect on cell growth. The NKLAM gene encodes a 62-kDa ring finger-containing protein that localizes to the cytoplasmic granules in NK cells. Further study of this gene may add to our understanding of cytotoxic processes common to NK cells, CTL, and activated macrophages.