Lymphoid apoptosis and myeloid hyperplasia in CCAAT displacement protein mutant mice

Abstract

CCAAT displacement protein (cux/CDP) is an atypical homeodomain protein that represses expression of several developmentally regulated lymphoid and myeloid genes in vitro, including gp91-phox, immunoglobulin heavy chain, the T-cell receptor ␤ and ␥ chains, and CD8. To determine how this activity affects cell development in vivo, a hypomorphic allele of cux/CDP was created by gene targeting. Homozygous mutant mice (cux/ CDP ⌬HD/⌬HD ) demonstrated a partial neonatal lethality phenotype. Surviving animals suffered from a wasting disease, which usually resulted in death between 2 and 3 weeks of age. Analysis of T lymphopoiesis demonstrated that cux/CDP ⌬HD/⌬HD mice had dramatically reduced thymic cellularity due to enhanced apoptosis, with a preferential loss of CD4 ؉ CD8 ؉ thymocytes. Ectopic CD25 expression was also observed in maturing thymocytes. B lymphopoiesis was also perturbed, with a 2-to 3-fold reduction in total bone marrow B-lineage cells and a preferential loss of cells in transition from pro-B/pre-BI to pre-BII stages due to enhanced apoptosis. These lymphoid abnormalities were independent of effects related to antigen receptor rearrangement. In contrast to the lymphoid demise, cux/CDP ⌬HD/⌬HD mice demonstrated myeloid hyperplasia. Bone marrow reconstitution experiments identified that many of the hematopoietic defects were linked to microenvironmental effects, suggesting that underexpression of survival factors or overexpression of death-inducing factors accounted for the phenotypes observed. Tumor necrosis factor (TNF) levels were elevated in several tissues, especially thymus, suggesting that TNF may be a target gene for cux/CDP-mediated repression. These data suggest that cux/CDP regulates normal hematopoiesis, in part, by modulating the levels of survival and/or apoptosis factors expressed by the microenvironment. (Blood. 2001;98:3658-3667)

CUX1, a haploinsufficient tumour suppressor gene overexpressed in advanced cancers

“…Mouse embryonic fibroblasts (MEFs) that were derived from Cux1 −/− mice showed a longer G1 phase and proliferated more slowly than their wild-type counterparts 21 . Myeloid hyperplasia was observed in bone marrow, the spleen and the peripheral blood of Cux1 −/− mice, an observation that fits well with frequent CUX1 LOH reported in MPDs 51 . By contrast, increased apoptosis was found to cause a twofold to threefold reduction in the percentage and absolute numbers of B cells and a fivefold reduction in thymo cytes in the thymus.…”

“…One gene inactivation strategy involved replacement of the CR3 exon with β-galactosidase coding sequences, to make a CUX1-LacZ fusion protein 35 . In the other strategy, a neomycin resistance (Neo) gene cassette with an in-frame termination codon was inserted in place of the CUT HD exon 50,51 . kb, kilobase; NLS, nuclear localization signal; nt, nucleotide.…”

“…1). As the protein remains in the cytoplasm, these mutations effectively inactivate the function of CUX1, as shown by the multiple phenotypes of two Cux1-knockout mouse models (discussed below) that were generated through a similar strategy 35,50,51 . In addition, approximately 40% of missense mutations were predicted to be deleterious by two independent algorithms 52,53 .…”

“…Two Cux1 mouse knockouts have been generated and have been analysed by several groups 35,50,51 . In both cases, the gene inactivation strategy led to the production of a protein that is truncated upstream of the CUT HD and is therefore not imported into the nucleus 35,50 .…”

“…By contrast, increased apoptosis was found to cause a twofold to threefold reduction in the percentage and absolute numbers of B cells and a fivefold reduction in thymo cytes in the thymus. Bone marrow reconstitution experiments indicated that both cell-intrinsic and microenvironmental effects were implicated in the demise of lymphoid cells, leading the authors to propose that CUX1 might upregulate survival factors or downregulate death-inducing factors 51 . Confirmation of these two hypotheses was later provided in an independent study showing that RNAi-mediated knockdown of CUX1 leads to upregulation and downregulation of tumour necrosis factor-α (TNFα) and BCL-2, respectively 14 .…”