Biomedical subjects

M V Kato

Publications and source records attributed to M V Kato.

23 records · Page 2Linked to original sources

PubMed1994

Inactivation of oncoprotein binding by a single Cys706-to-Tyr substitution in the retinoblastoma protein.

We previously found a new single amino acid substitution at codon 706 (Cys-to-Tyr) of the retinoblastoma (RB) gene in a sporadic retinoblastoma patient. The glutathione S-transferase-RB fused protein containing this mutation was here tested for binding to SV40 large T antigen and adenovirus E1A protein, and was shown to have lost its binding affinity. Thus, Tyr, as well as Phe, residues substituted for Cys706 were found to abolish the RB protein activity.

Adenovirus E1A Proteins↗

PubMed1994

Mutations in the retinoblastoma gene and their expression in somatic and tumor cells of patients with hereditary retinoblastoma.

Two intragenic deletions (exon 18-19 and exon 24) and two point mutations (one missense mutation in exon 21 and one mutation at splice-donor site for exon 13) were detected in the retinoblastoma gene in somatic and tumor cells of patients with hereditary retinoblastoma. Three mutations were located in a domain essential for binding to oncoproteins encoded by DNA tumor viruses (Hu et al., 1990; Huang et al., 1990). One mutation (deletion of exon 24) was outside this domain but it is in the region essential for binding to transcriptional factor E2F, and for suppression of malignant phenotypes (Qian et al., 1992; Qin et al., 1992). A minisatellite-like sequence and short repeated sequences were located at the breakpoint of the deletion of exon 24, suggesting that two deletions on both sides of the minisatellite-like sequence may be generated by a "DNA slippage and misalignment" mechanism. Upon amplification of cDNA by the polymerase chain reaction, no transcript of gene with frameshift mutation (deletion of exon 24) was detected in skin fibroblasts, while transcripts of genes with missense mutations were detected. The results, in combination with previous reports (Dunn et al., 1989; Hashimoto et al., 1991), suggest the instability of transcripts with a premature stop codon or the suppressed expression of alleles with a premature stop codon in the retinoblastoma gene in somatic cells of hereditary patients.

Amino Acid Sequence↗

PubMed1994

Parental origin of germ-line and somatic mutations in the retinoblastoma gene.

Segregation analysis of polymorphic sites within the retinoblastoma (RB) gene and on chromosome 13, as well as the parental origin of the lost allele in the tumor, were analyzed in 24 families with RB patients. Four mutant alleles transmitted through the germ-line and seven de novo germ-line mutant alleles were identified in 11 patients with hereditary RB. Segregation analysis within the RB gene and on chromosome 13 was useful for DNA diagnosis of susceptibility to RB in relatives of hereditary patients, even if mutations were not identified. All seven de novo germ-line mutant alleles were paternally derived. The bias toward the paternal allele for de novo germ-line mutations of the RB gene was statistically significant. Seven paternal alleles and six maternal alleles were lost in 13 non-hereditary RB tumors with no bias in the parental origin of the somatic allele loss. These results suggest that the physical environment or a deficiency in DNA repair during spermatogenesis may be associated with significant risk factors for de novo germ-line mutations.

Alleles↗

PubMed1994

Detection of mutations of the RB1 gene in retinoblastoma patients by using exon-by-exon PCR-SSCP analysis.

Most sporadic cases of retinoblastoma, malignant eye tumor of children, may require the identification of a mutation of the retinoblastoma gene (RB1 gene) for precise genetic counseling. We established a mutation detection system of and screened for the RB1 gene mutation in 24 patients with retinoblastoma--12 bilateral patients and 12 unilateral patients. Mutation analysis was performed by PCR-mediated SSCP analysis in the entire coding region and promoter region, as an initial screening method, followed by direct genomic sequencing. Possible oncogenic mutations were identified in 14 (58%) of 24 tumors, of which 6 were single base substitutions, 4 were small deletions, 3 were small insertions, and 1 was a complex alteration due to deletion-insertion. A constitutional somatic mosaicism was suggested in one bilateral patient. A majority (57%) of mutations were found in E1A binding domains, and all were presumed to truncate the normal gene products. The mutation analysis presented here may provide a basis for the screening system of RB1 gene mutations in retinoblastoma patients.

Base Sequence↗

PubMed1993

Loss of heterozygosity on chromosome 13 and its association with delayed growth of retinoblastoma.

Loss of heterozygosity (LOH) on chromosome 13 and the age of patients at operation were studied in 46 cases of retinoblastoma (RB) tumors, of which 25 were hereditary and 21 were non-hereditary. The frequency of LOH was 70% for all informative tumors, but significantly higher in non-hereditary tumors (90%) than in hereditary ones (52%). Our results suggest that LOH might be involved in the initial somatic events in non-hereditary tumors. Age at operation of patients with hereditary tumors was significantly lower than that of patients with non-hereditary tumors. Even when tumors associated with a family history were omitted from among the hereditary cases, the difference was still significant. In the case of hereditary tumors, age at operation of LOH-negative patients was significantly lower than that of LOH-positive patients. When tumors associated with a family history were omitted, the difference was still significant. The delay in development of LOH-positive tumors suggests that LOH for one chromosome 13 may be disadvantageous with respect to growth of RB tumors.

Age Factors↗