metallothionein and Leukemia--T-Cell

The p210bcr/abl chimeric protein is considered to be implicated in the pathogenesis of Philadelphia chromosome-positive human leukemias. To investigate its biologic function in vivo, we generated transgenic mice expressing p210bcr/abl driven by the metallothionein enhancer/promoter. Two of six founder mice and the transgenic progeny developed leukemias several months after birth. In the leukemic tissues, the expression of the p210bcr/abl transgene product was detected and the increased tyrosine-phosphorylation of cellular proteins was observed. The expressed p210bcr/abl transgene product was shown to possess an enhanced kinase activity. The leukemic cells showed rearrangements in the T-cell receptor loci, indicating that the leukemic cells were monoclonal and committed to the T-cell lineage. Polymerase chain reaction analysis for tissue distribution of p210bcr/abl expression showed that, in the transgenic line that reproducibly developed leukemias, p210bcr/abl was expressed in the hematopoietic tissues such as thymus and spleen; on the other hand, in the transgenic lines that have not developed leukemias, p210bcr/abl expression was detected only in the nonhematopoietic tissues such as the brain and kidney. These results suggest that the tumorigenicity of the p210bcr/abl chimeric protein is restricted to the hematopoietic tissues in vivo and that an event enhancing p210bcr/abl expression contributed a proliferative advantage to hematopoietic precursor cells and eventually developed T-cell leukemia in transgenic mice.

Topics: Animals; Base Sequence; Clone Cells; DNA Primers; Female; Fusion Proteins, bcr-abl; Gene Expression Regulation, Neoplastic; Gene Rearrangement, beta-Chain T-Cell Antigen Receptor; Gene Rearrangement, gamma-Chain T-Cell Antigen Receptor; Genes, abl; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Leukemia, T-Cell; Male; Metallothionein; Mice; Mice, Transgenic; Molecular Sequence Data; Pedigree; Phosphotyrosine; Promoter Regions, Genetic; Receptors, Antigen, T-Cell, alpha-beta; Receptors, Antigen, T-Cell, gamma-delta; RNA, Messenger; Tissue Distribution; Tyrosine

Rhombotin-2 (RBTN-2) is a LIM domain protein that, with the exception of thymocytes, is widely expressed during fetal development. Although RBTN-2 is crucial for normal erythropoiesis, the ectopic expression of RBTN-2 in T lymphocytes results in T-cell proliferation and leukemogenesis. Thus, while a proliferative function for RBTN-2 has been established in T-cells, neither its role in erythropoiesis nor its function(s) in other tissues are known. We have examined the expression and location of RBTN-2 in normal and malignant cells. Similar to fetal development, RBTN-2 RNA was detected in all normal adult tissues tested with the exception of colon and thymocytes. RBTN-2 RNA was not detected in all primary tumors and tumor cell lines, indicating RBTN-2 expression is not ubiquitous in proliferating cells. Using polyclonal antisera, RBTN-2 was detected predominantly in the nucleus of human hematopoietic cells. Significantly, human leukemic T cells with disruption of the RBTN-2 locus and thymocytes from transgenic mice with enforced expression of RBTN-2 showed similar nuclear location of RBTN-2 protein, consistent with the notion that RBTN-2 acts as a transcriptional regulator in T-cell proliferation. Surprisingly, in normal tissues, RBTN-2 showed a strikingly similar distribution to that of metallothionein-1, having both nuclear and cytoplasmic localization that suggested that RBTN-2 may be involved in the acute phase response. Indeed, similar to metallothionein-1, RBTN-2 mRNA was induced in thymocytes of mice exposed to zinc and in human thymocytes treated with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate. Since the LIM domain permits binding of multiple protein partners, the specific function of RBTN-2 may depend upon subcellular sequestration through interaction with different cofactors. Thus, in addition to its roles in erythropoiesis and T-cell leukemia, RBTN-2 may also be involved in the acute phase response.

Topics: Acute-Phase Proteins; Adaptor Proteins, Signal Transducing; Adult; Animals; Brain Chemistry; Cell Nucleus; Child, Preschool; Cycloheximide; DNA-Binding Proteins; Erythropoiesis; Gene Expression Regulation; Humans; Kidney; Leukemia, T-Cell; LIM Domain Proteins; Liver; Metalloproteins; Metallothionein; Mice; Mice, Inbred C57BL; Mice, Transgenic; Proto-Oncogene Mas; Proto-Oncogene Proteins; Proto-Oncogenes; RNA, Messenger; RNA, Neoplasm; Tetradecanoylphorbol Acetate; Thymus Gland; Tumor Cells, Cultured; Zinc