til-1: a novel proviral insertion locus for Moloney murine leukaemia virus in lymphomas of CD2-myc transgenic mice

Abstract

Moloney murine leukaemia virus (MoMLV) markedly accelerates thymic lymphoma development in mice carrying a transgene in which the human c-myc gene is linked to the CD2 locus control region. To investigate the mechanism of synergy and identify the genes which collaborate with myc in these clonal tumours, we analysed the sites of MoMLV insertion. Analysis of known viral integration loci revealed only a small number of insertions at bmi-1, pim-1 and ahi-1. Further cloning and hybridization analysis revealed a new common integration locus, designated till, which was occupied in 25 out of 77 lymphomas examined, with evidence of multiple clonal insertions in some cases. Mapping relative to established chromosomal markers in interspecific backcross mice located till to mouse chromosome 17, distal to pim-1 and tic-1. These results suggest that the til-1 locus may harbour a novel myecollaborating gene which acts as a target for activation in T cell lymphomas.Proviral insertional mutagenesis is a pivotal event in oncogenesis by murine leukaemia virus (MLV) and the study of viral insertion sites in MLV-induced turnouts has led to the identification of a large number of host cell genes relevant to this process (Kung et al., 1991).Moreover, the discovery that transgenic mice carrying a dominant oncogene develop tumours much more rapidly if infected early in life with MLV has provided a powerful approach to the identification and complementation mapping of the host cell genes which drive the multi-step evolution of lymphomas (Berns, 1994). As an example, Eta-myc mice developed B cell lymphomas very rapidly after infection with Moloney MLV (MoMLV), with frequent insertions at several distinct host cell loci including pim-1, pal-1, bmi-1 and bla- 1 (van Lohuizen et al., 1991). The importance of these insertions to lymphoma development has been amply confirmed for pim-1 and bmi-1, both of which can act independently as dominant oncogenes and are strongly synergistic with myc in lymphomagenesis van Lohuizen et al., 1989;Haupt et al., 1993). Moreover, a reciprocal pattern of gene activation was seen in pim-1 transgenic mice which developed low incidence lymphomas that could be accelerated by neonatal infection with * Author for correspondence. Fax +44 141 330 6467. e-mail gpma03 @udcf.gla.ac.uk MoMLV, with concomitant insertions at c-myc, N-myc and paL1 loci (van Lohuizen et al., 1989).To test the effects of overexpressing c-myc in the T cell lineage, we developed a transgenic model in which the human c-myc oncogene was linked to a T cell-specific regulatory element, the locus control region from the human CD2 gene. We found that CD2-myc transgenic lines developed thymic lymphomas at low frequency and that neonatal infection with MoMLV dramatically accelerated this process, leading to 100% tumour incidence within 80 days of birth (Stewart et al., 1993).The tumours were of a homogeneous T cell phenotype (CD3 +, CD8 +, CD4 +/ ), invariably expressed the transgene and contained clonal integrations of MoMLV. Surprisingly, an initial ...

A full-length Cbfa1 gene product perturbs T-cell development and promotes lymphomagenesis in synergy with MYC

“…Our previous studies identi®ed the Cbfa1 gene as a frequent target for transcriptional activation by Moloney murine leukaemia virus in lymphomas of CD2-myc mice and showed that the over-expressed gene encodes multiple isoforms, the most abundant of which is G1 (Stewart et al, 1996(Stewart et al, , 1997. Moreover, we have found that over-expression of Cbfa1 in the thymus perturbs T-cell development, causing a pronounced skew towards CD8SP thymocytes.…”

“…As we identi®ed the til-1/Cbfa1 gene as a potential myc-collaborating gene (Stewart et al, 1996(Stewart et al, , 1997 we assessed the e ect of crossing CD2-Cbfa1-G1 mice with CD2-myc transgenic animals. CD2-myc mice develop T-cell tumours, primarily involving the thymus, at an incidence of around 30% by 12 months of age depending on the genetic background (Stewart et al, 1993).…”

RUNX3 is multifunctional in carcinogenesis of multiple solid tumors

“…The CD2-MYC mice selectively express the c-MYC oncogene in T cells. Although uninfected mice develop tumors infrequently, murine leukemia virus infection at birth accelerates tumor onset: all infected mice succumb to thymic lymphomas by 80 days (Stewart et al, 1996). After screening the viral-induced thymic lymphomas, a proviral integration site was uncovered 30 kb upstream of the Runx3 distal P1 promoter.…”

Runx2: A novel oncogenic effector revealed by in vivo complementation and retroviral tagging

“…Instead, we de®ned the Til1 locus as a common target in a signi®cant proportion of tumours and we have subsequently shown that these insertions activate transcription of the Runx2/Cbfa1/Aml3/Pebp2aA gene (hereafter Runx2) (Stewart et al, 1996(Stewart et al, , 1997. By a similar approach, Girard et al (1996) showed that Notch1 is the preferred target for viral acceleration/ activation in their MMTVd-Myc transgenic model.…”