Acceleration of chronic myeloproliferation by enforced expression of Meis1 or Meis3 in Icsbp-deficient bone marrow cells.

Identifying genetic pathways that cooperate in leukemogenesis facilitates our understanding of the molecular mechanisms at play. Interferon consensus sequence-binding protein (ICSBP) is a tumor suppressor, whose downregulation cooperates with BCR-ABL and NUP98-TOP1 gene products to accelerate leukemia induction in mouse models. Similarly, Meis1 synergizes with HoxA9 or NUP98-HOX (but not NUP98-TOP1) fusion genes to promote the early onset of leukemia. To investigate whether Icsbp deficiency interacts with Meis1 or its family member Meis3, we transplanted Icsbp(-/-) bone marrow (BM) cells after transduction with Meis1 or Meis3 retroviral vectors. Here, we show that enforced expression of Meis1 or Meis3 in Icsbp(-/-) BM cells induces a fatal, invasive myeloproliferative disease. Secondary mutations, such as activation of Mn1, led to the progression to acute myeloid leukemia in a few mice. Interestingly, expression of endogenous Meis1 and Meis3 mRNAs was repressed in the granulocytic progenitor population of Icsbp(-/-) mice. These results reveal a novel collaboration between Icsbp deficiency and Meis1/Meis3 in the acceleration of chronic myeloid leukemia-like disease.

Aberrations of the p53 tumor suppressor gene in various tumors in dogs.

OBJECTIVE: To evaluate aberrations of the p53 tumor suppressor gene in naturally developing tumors in dogs. SAMPLE POPULATION: Tumor specimens from 15 dogs with various tumors, including malignant lymphoma (7 dogs), monocytic leukemia (1), mammary gland adenoma (1), mammary gland benign mixed tumor (1), rhabdomyosarcoma (1), colon cancer (1), and osteosarcoma (3). PROCEDURE: Aberrations of the p53 gene in these tumor tissues were examined by reverse transcriptase-polymerase chain reaction and single-strand conformation polymorphism analysis, using 3 fragments that covered the entire open reading frame of the canine p53 gene, followed by nucleotide sequencing of the abnormal bands. RESULTS: Point mutations, deletions, and insertions resulting in a number of amino acid substitutions of wild-type p53 were detected in 7 of the 15 tumor specimens from dogs with malignant lymphoma, monocytic leukemia, rhabdomyosarcoma, colon cancer, and osteosarcoma. Of these 7 dogs, 2 had aberrations of the p53 gene on both alleles, whereas 5 had aberrations of the p53 gene on 1 allele and concurrently lacked the wild-type p53 transcript. Many of the aberrations of the p53 gene detected in these tumors were located in the transactivation, DNA binding, and oligomerization domains. CONCLUSIONS AND CLINICAL RELEVANCE: Various naturally developing tumors in dogs often have inactivation of the p53 tumor suppressor gene, which may be 1 of the multiple step-wise genetic changes during tumorigenesis. This study indicates that p53 gene can be a target for gene therapy for tumors in dogs.

Identification of podocalyxin-like protein 1 as a novel cell surface marker for hemangioblasts in the murine aorta-gonad-mesonephros region.

Recent studies with avian embryos and murine embryonic stem cells have suggested that hematopoietic cells are derived from hemangioblasts, the common precursors of hematopoietic and endothelial cells. We molecularly cloned podocalyxin-like protein 1 (PCLP1) as a novel surface marker for endothelial-like cells in the aorta-gonad-mesonephros (AGM) region of mouse embryos, where long-term repopulating hematopoietic stem cells (LTR-HSCs) are known to arise. PCLP1+ CD45 cells in the AGM region incorporated acetylated low-density lipoprotein and produced both hematopoietic and endothelial cells when cocultured with OP9 stromal cells. Moreover, multiple lineages of hematopoietic cells were generated in vivo when PCLP1 +CD45-cells were injected into neonatal liver of busulfan-treated mice. Thus, PCLP1 can be used to separate hemangioblasts that give rise to LTR-HSCs.

Cloning and chromosome mapping of the feline genes p21WAF1 and p27Kip1.

For investigation of the relation of cell cycle regulation with tumorigenesis in cats, we carried out molecular cloning of feline p21WAF1 and p27Kip1 cDNAs and chromosomal mapping of these genes on the cat genome. The feline p21WAF1 cDNA clone obtained in this study encoded 164 amino acids (aa) showing 83.5% and 76.8% sequence similarity with those of the human and mouse counterparts, respectively. The cat p27Kip1 cDNA clone isolated here encoded 198 aa, showing sequence similarities of 93.4% and 90.4% with its human and mouse counterparts, respectively. Using a panel of feline x rodent somatic cell hybrids, the feline CDKN1A (p21WAF1) and CDKN1B (p27Kip1) loci were assigned to feline chromosomes B2 and B4, respectively. Southern-blot analyses of 17 feline spontaneous leukemia and lymphoma cases using these cDNAs as probes did not reveal any rearrangements in either the p21WAF1 or the p27Kip1 gene. RT-PCR/SSCP (single strand conformation polymorphism) analysis of p27Kip1 cDNA did not uncover any amino acid substitutions in the 10 feline leukemia and lymphoma cases that were examined.

Cloning of feline p21WAF1 and p27Kip1 cDNAs and search for their aberration in leukemias and lymphomas in cats.

For investigation of the relation of cell cycle regulation with tumorigenesis in cats, we cloned feline p21WAF1 and p27Kip1 cDNAs and searched for their aberration in feline spontaneous leukemias and lymphomas. The feline p21WAF1 cDNA (pCFW.31) clone obtained from the PCR amplified product appeared to cover approximately 75% of the open reading frame, and showed 81.6% and 76.8% sequence similarities with those of human and mouse counterparts, respectively. The pHFK.5 clone isolated by plaque hybridization contained the whole open reading frame of cat p27Kip1 cDNA encoding 198 amino acids, showing 93.4% and 90.4% sequence similarities with those of human and mouse counterparts, respectively. Southern-blot analyses using these clones as probes did not show any deletion or rearrangement of both the p21WAF1 and p27Kip1 genes in 19 feline spontaneous cases of leukemias and lymphomas examined. RT-PCR/SSCP (single strand conformation polymorphism) analysis of p27Kip1 cDNA indicated that there was no mutation resulting in amino-acid substitution in 10 feline leukemia and lymphoma cases.