Constitutive activation ofStat5aby retrovirus integration in early pre-B lymphomas of SL/Kh strain mice

Abstract

We found that the second intron of Stat5a was one of the common integration sites of the endogenous ecotropic murine leukemia virus, i.e., SL͞Kh virus integration-1 (Svi1), in early pre-B lymphomas in SL͞Kh mice. The high expression of STAT5A induced by Svi1 integration and activation accelerated the transcription of its target genes such as c-Myc. Transfection of the constitutively active Stat5a mutant cDNA, but not of the wild-type cDNA, to the bone marrow cells induced colony formation of pre-B cells in a methylcellulose medium and escaped from dependence on IL-7. Such growth depended on a genetic factor in the SL͞Kh strain. Consitutively high expression of Stat5a either by retrovirus integration or transfection of active mutant cDNA can be lymphomagenic to early pre-B cells in collaboration with a certain genetic background factor of mice.provirus ͉ hot spot ͉ lymphomagenesis T he SL͞Kh strain of mice develop spontaneous pre-B lymphomas at Ͼ90% incidence by 6 mo of age (1, 2). There are two morphological distinct types: the major lymphomas, which show systemic lymphatic tissue involvement, and the minor type, which shows restricted growth in bone marrow (BM) (1). Both are pre-B lymphomas expressing BP-1 and B220 (2, 3). Several lines of evidence indicate that the endogenous murine leukemia virus (MuLV) plays an etiologic role in SL͞Kh lymphomas; in particular, somatically acquired proviruses frequently are observed in lymphoma DNAs (3, 4).To elucidate the mechanism of lymphomagenesis, we cloned the virus-host junctional segments from lymphoma DNAs by an inverse PCR technique and performed sequence analysis. In three of 60 SL͞Kh lymphomas, clonal ecotropic provirus integration was found within a 400-bp stretch in the second intron of the Stat5a gene, a member of the STAT family. In this article, we examined the effect of the provirus integration in this hot spot, named SL͞Kh virus integration-1 (Svi1). The effect of the constitutive high expression of Stat5a on early B cells was further verified by colonial growth of early pre-B cells in soft agar medium and loss of IL-7 dependence, when SL͞Kh BM cells were transfected with an active Stat5a mutant cDNA. It was shown that the immortalization of early pre-B cells by Stat5a depended on an unidentified host factor in SL͞Kh mice. There are several reports on the relevance of Stat5a in hemopoietic malignancies (5-12). Stat5b is a human myeloid cell oncogene, but neither Stat family member has been shown to have a direct pathogenetic role in lymphoid disease. Herein, we report that Stat5a is one of the hot spots of MuLV integration and subsequent constitutive up-regulation of Stat5a perturbs signaling in early B lineage leading to lymphoma development in a certain genetic background. Materials and MethodsMice. SL͞Kh is an inbred strain of mice with a high incidence of spontaneous pre-B lymphomas. Previously, we reported their origin (13) and virus expression (1), the pathology of lymphomas (1, 2), and host genetic factors in lymphomagenesis (3,4,14). They were maint...

Multiple pathways contribute to the hyperproliferative responses from truncated granulocyte colony-stimulating factor receptors

“…59 The results presented here showing sustained STAT5 activation downstream of JAK2 as a crucial mediator of the hyperproliferative responses from truncated G-CSF-Rs associated with AML further emphasizes the importance of the JAK2-STAT5 module in malignancy -a role that has apparently been conserved throughout evolution. 59,60 This is perhaps not surprising given the important cell cycle regulators known to be stimulated by STAT5, including cyclin D1 61 and c-myc, 62 not to mention its positive effects on cell survival mediators, such as bcl-XL and bcl-2. 56,63 Together, this suggests that suppression of STAT5 function may represent an important general strategy in the treatment of leukemias and other cancers.…”

Pre‐B lymphomas in SL/Kh mice: A multifactorial disease model

“…10) After 72 h, colonial growth was observed only from the BM transfected with 1 * 6-Stat5a cDNA, but not with wild-type Stat5a cDNA or an empty vector (Fig. 1B).…”

“…Phosphorylation signals for Stat5a come from the IL7-receptor and the pre-B cell receptors. Stimulation of Svi1 lymphoma cells with antibodies to IL7R 10) or Igα induced transient phosphorylation of Stat5a and thereby increased affinity to the GAS element and transcription of the target genes. Signaling through Igα is specifically inhibited by PP2, an inhibitor to Src kinase, but not by picetannol, an inhibitor to Syk kinase (Tasuruyama et al, unpublished observation).…”

“…Svi1 is an integration into the second intron of Stat5a, 10) found in 7 out of 120 SL/Kh lymphomas (Fig. 1A).…”

HIV-1 Selectively Integrates Into Host DNA In Vitro

“…In the present study, we aimed to establish an in vitro integration assay using www.intechopen.com HIV-1 Selectively Integrates Into Host DNA In Vitro 307 retroviral cDNA and integrase. Yoshinaga et al previously reported the development of an in vitro integration assay using recombinant HIV-1 integrase, and short viral and target DNA sequences [9]. Using this method, they successfully detected retroviral cDNA-target DNA complexes in vitro and reported that the dinucleotide motif 5'-CA that is located at the proviral genome termini was essential for HIV-1 integration.…”