Showing papers by "Xiaoyan Jiang published in 2002"

Elucidating critical mechanisms of deregulated stem cell turnover in the chronic phase of chronic myeloid leukemia

Abstract: Chronic myeloid leukemia (CML) has been studied intensively for many years; yet its treatment remains problematic and its biology remains elusive. In chronic phase, the leukemic clone appears to be maintained by a small number of BCR-ABL-positive hematopoietic stem cells that differentiate normally and amplify slowly. In contrast, as these cells enter the intermediate stages of lineage restriction, their progeny are selectively expanded and generate an enlarged pool of neoplastic progenitors. Recent analyses of purified subsets of primitive CML cells have provided a coherent explanation for this dichotomous behavior of BCR-ABL-positive stem and progenitor cells based on the discovery of an unusual autocrine IL-3/G-CSF mechanism activated in them. This only partially counteracts in vivosignals that maintain normal stem cells in a quiescent state but, when active in CML stem cells, promotes their differentiation in favor of their self-renewal. In more differentiated CML progenitors, the same mechanism has a more potent mitogenic effect which is then extinguished when the cells enter the terminal stages of differentiation. Thus, further expansion of the clone is limited until inevitably additional mutations are acquired that further distort or override the regulatory mechanisms still operative in the chronic phase.

Ahi-1, a Novel Gene Encoding a Modular Protein with WD40-Repeat and SH3 Domains, Is Targeted by the Ahi-1 and Mis-2 Provirus Integrations

Abstract: The Ahi-1 locus was initially identified as a common helper provirus integration site in Abelson pre-B-cell lymphomas and shown to be closely linked to the c- myb proto-oncogene. Since no significant alteration of c- myb expression was found in Abelson murine leukemia virus-induced pre-B-lymphomas harboring a provirus inserted within the Ahi-1 locus, this suggested that it harbors another gene whose dysregulation is involved in tumor formation. Here we report the identification of a novel gene ( Ahi-1 ) targeted by these provirus insertional mutations and the cloning of its cDNA. The Ahi-1 proviral insertions were found at the 3′ end of the gene, in an inverse transcriptional orientation, with most of them located around and downstream of the last exon, whereas another insertion was within intron 22. In addition, another previously identified provirus insertion site, Mis-2, was found to map within the 16th intron of the Ahi-1 gene. The Ahi-1 cDNA encodes a 1,047-amino-acid protein. The predicted Ahi-1 protein is a modular protein that contains one SH3 motif and seven WD40 repeats. The Ahi-1 gene is conserved in mammals and encodes two major RNA species of 5 and 4.2 kb and several other shorter splicing variants. The Ahi-1 gene is expressed in mouse embryos and in several organs of the mouse and rat, notably at high levels in the brain and testes. In tumor cells harboring insertional mutations in Ahi-1 , truncated Ahi-1 /viral fused transcripts were identified, including some splicing variants with deletion of the SH3 domain. Therefore, Ahi-1 is a novel gene targeted by provirus insertion and encoding a protein that exhibits several features of a signaling molecule. Thus, Ahi-1 may play an important role in signal transduction in normal cells and may be involved in tumor development, possibly in cooperation with other oncogenes (such as v- abl and c- myc ) or with a tumor suppressor gene ( Nf1 ), since Ahi-1 insertion sites were identified in tumors harboring v- abl defective retroviruses or a c- myc transgene or in tumors exhibiting deletion of Nf1 .