RESUMO
Chronic myelogenous leukemia (CML) is characterized by the presence of a novel fusion gene comprised of portions of the BCR gene from chromosome (ch) 22 and the ABL gene from ch 9. The present study was designed to identify regulatory DNA regions as determined by DNAase I hypersensitivity to address the question of whether altered chromatin contributes to changes in ABL expression. We identify five hypersensitive (HS) sites within the abnormal BCR/ABL allele in K562 cells in a pattern different from the normal BCR. The pattern of hypersensitivity is modified when the cells undergo hemin induced differentiation. These results indicate that the normal BCR has a chromatin configuration consistent with active transcription and that the BCR/ABL fusion gene chromatin is different. This may be important in the pathogenesis of CML.
Assuntos
Cromatina/ultraestrutura , DNA de Neoplasias/genética , Proteínas de Fusão bcr-abl/genética , Leucemia Mielogênica Crônica BCR-ABL Positiva/genética , Proteína Oncogênica p21(ras)/genética , Cromossomos Humanos Par 22 , Cromossomos Humanos Par 9 , Sondas de DNA , Desoxirribonuclease BamHI , Desoxirribonuclease EcoRI , Desoxirribonuclease I , Desoxirribonucleases de Sítio Específico do Tipo II , Amplificação de Genes , Hemina/farmacologia , Humanos , Hibridização de Ácido Nucleico , Cromossomo Filadélfia , Mapeamento por Restrição , Translocação Genética , Células Tumorais CultivadasRESUMO
Previous studies of the Hpa I cleavage site-sickle cell hemoglobin gene linkage in various African populations suggested that the sickle gene arose independently more than once. In the present study we have performed restriction endonuclease haplotype analysis for the beta-globin-like gene cluster from four separate geographic areas in Africa, all of which possess the sickle gene. In Benin (Central West Africa) and Algeria (Arab North Africa) all chromosomes carrying the sickle gene possess an identical haplotype as defined by 11 different polymorphic restriction endonuclease sites within the 60-kilobase region of the beta-globin-like gene cluster. In the Central African Republic (Bantu-speaking Africa) and in Senegal (Atlantic West Africa) a very large proportion of the sickle gene chromosomes were associated with a haplotype specific for each country. Thus, three different haplotypes are shown to be associated with the sickle gene in Africa, and each is present at a very high frequency in geographically separate regions. Since the three haplotypes differ from each other by at least three sites residing both 5' and 3' to a putative hot spot for recombination, it is most likely that the sickle gene arose at least three times on separate preexisting chromosomal haplotypes. This may have implications for a better understanding of the variable nature of the expression of sickle cell anemia, because clinically relevant sequences (for example, gamma-globin gene regulatory sequences responsive to anemia) might be linked polymorphically to these haplotypes.
