1. Field of the Invention
The present invention relates to novel antiproliferative genes. More specifically, isolated nucleic acid molecules are provided encoding the human B-cell translocation genes 2 and 3 (BTG-2 and BTG-3). BTG-2 and BTG-3 polypeptides are also provided, as are vectors, host cells and recombinant methods for producing the same.
2. Related Art
In normal tissues, homeostasis is maintained through negative and positive growth controls which effect the proliferation and differentiation related to cellular genetic programs. An alteration of this subtle balance can result in developmental abnormalities or in neoplasia. Proto-oncogenes, genes that promote cell division, were the first growth-inducing elements to be identified and more than sixty of them have been described so far (Bishop, J. M., Cell 64:235:248 (1991)). The genes that negatively regulate cell proliferation are crucial to counteract the growth-inducing elements and are likely to have the same importance as proto-oncogenes in controlling cell division (Marshall, C. J., Cell 64:313-326 (1991)), especially since the loss of their function has been reported to be associated with irregular cellular differentiation and proliferation or with alteration of embryonic development (Weinberg, R. A., Science 254:1138-1146 (1991)).
The polynucleotides and polypeptides of the present invention are thought to be members of a family of anti-proliferative genes. BTG-1 is a member of this group and has been cloned and expressed. (Rovault, J. P. et al., The EMBO Journal 11(4):1663-1670 (1992)). BTG-1 was shown to negatively regulate NIH3T3 cell proliferation when over- or inappropriately expressed. BTG stands for B-cell translocation gene, and the BTG-1 gene has been shown to be involved in a chromosomal translocation [t(8;12)(q24;22)] in B-cell chronic lymphocytic leukemia.
The BTG-1 open reading frame is 60% homologous to PC3, an immediate early gene induced by nerve growth factor in rat PC12 cells. Sequence and Northern blot analyses indicate that BTG-1 and PC3 are not cognate genes but are thought to be members of this new family of anti-proliferation genes. The BTG-1 gene is preferentially expressed in quiescent cells during the early sub-phases of G.sub.1 in a serum-dependent manner and it is then down-regulated to reach a minimum level as the cells enter the S phase. This suggests a functional link between BTG-1 and the cell cycle process. BTG-1 is expressed in tissues (lymphoid, liver, placenta) containing non-dividing cells likely to re-enter the cell cycle upon different stimuli, whereas the expression of BTG-1 is barely detectable in fully differentiated tissues such as brain and muscle.
The BTG-1 gene was shown to be highly conserved in evolution and a similar 1.8 Kb transcript can be detected in murine and chicken tissue by using a human BTG-1 DNA probe (Rimokh, R. et al., Genes Chrom. Cancer 3:24-36 (1991)).
The BTG-2 and BTG-3 genes and gene products have been putatively identified as members of this family as a result of amino acid sequence homology to BTG-1.