MB Valentine

The tandemly linked p16INK4aMTS1 and p15INK4b/MTS2 genes on chromosome 9, band p21 encode proteins that function as specific inhibitors of the cyclin D-dependent kinases CDK4 and CDK6. This locus undergoes frequent bi-allelic deletion in human cancer cell lines, suggesting that the encoded proteins may function as tumor suppressors. However, more recent analysis of primary tumor samples has shown a much lower frequency of abnormalities affecting this region, raising doubt over the importance of these proteins in human malignancies. Hemizygous deletions and rearrangements of chromosome 9, band p21, are among the most frequent cytogenetic abnormalities detected in pediatric acute lymphoblastic leukemia (ALL), occurring in approximately 10% of cases. To determine if the p16INK4a/p15INK4b locus might be the target of these chromosomal lesions, we analyzed both genes in primary clinical samples from 43 pediatric ALL patients using interphase fluorescence in situ hybridization, Southern blot analysis, and the polymerase chain reaction. Deletions of p16INK4a/p15INK4b were identified in 18 of 20 cases with cytogenetically observed abnormalities of 9p and 5 of 23 with apparently normal chromosomes 9p, with the majority containing bi-allelic deletions (16 homozygous/7 hemizygous). Although most homozygous deletions involved both genes, Southern blot analysis showed an interstitial deletion in a single case that was confined to p16INK4a, suggesting that p15INK4b was not the critical target gene in this case. Sequence analysis of both p16INK4a and p15INK4b in all seven cases with hemizygous deletions failed to show mutations within the coding regions of the retained alleles. In this select group of patients, deletion of p16INK4a/p15INK4b was associated with T-cell phenotype, nonhyperdiploid karyotype (< 50 chromosomes), and poor event-free survival. These findings indicate that deletion of the p16INK4a/p15INK4b locus is one of the most common genetic abnormalities so far detected in pediatric ALL, and that loss of one or more of these cell cycle kinase inhibitors is important in leukemogenesis.

Human macrophage colony-stimulating factor (CSF-1 or M-CSF) is encoded by a single gene that was previously assigned to the long arm of chromosome 5, band q33.1, in a region adjacent to the gene encoding its receptor (Pettenati MJ, et al, Proc Natl Acad Sci USA 84:2970, 1987). Using fluorescence in situ hybridization with genomic probes to examine normal metaphase chromosomes, we reassigned the human CSF1 gene to the short arm of chromosome 1, bands p13-p21. We confirmed this result by hybridizing a CSF1 cDNA probe to filters containing flow-sorted chromosomes and by identifying CSF1 sequences in DNAs extracted from human x rodent somatic cell hybrids that contained human chromosome 1 but not human chromosome 5. Our findings are consistent with studies that have shown tight linkage between the murine CSF1 and amylase genes, as part of a conserved linkage group between mouse chromosome 3 and the short arm of human chromosome 1, which also includes the genes encoding the beta subunits of thyrotropin and nerve growth factor. Assignment of the CSF1 gene to chromosome 1 at bands p13-p21 raises the possibility that it may be altered by certain nonrandom chromosomal abnormalities arising in human hematopoietic malignancies and solid tumors.

Human macrophage colony-stimulating factor (CSF-1 or M-CSF) is encoded by a single gene that was previously assigned to the long arm of chromosome 5, band q33.1, in a region adjacent to the gene encoding its receptor (Pettenati MJ, et al, Proc Natl Acad Sci USA 84:2970, 1987). Using fluorescence in situ hybridization with genomic probes to examine normal metaphase chromosomes, we reassigned the human CSF1 gene to the short arm of chromosome 1, bands p13-p21. We confirmed this result by hybridizing a CSF1 cDNA probe to filters containing flow-sorted chromosomes and by identifying CSF1 sequences in DNAs extracted from human x rodent somatic cell hybrids that contained human chromosome 1 but not human chromosome 5. Our findings are consistent with studies that have shown tight linkage between the murine CSF1 and amylase genes, as part of a conserved linkage group between mouse chromosome 3 and the short arm of human chromosome 1, which also includes the genes encoding the beta subunits of thyrotropin and nerve growth factor. Assignment of the CSF1 gene to chromosome 1 at bands p13-p21 raises the possibility that it may be altered by certain nonrandom chromosomal abnormalities arising in human hematopoietic malignancies and solid tumors.