Characterization of nuclear factors that bind to the human thymidylate synthase gene in HL-60 cells differentiated by all-trans retinoic acid treatment

Correlation between thymidylate synthase gene variants, RNA and protein levels in primary colorectal adenocarcinomas

This study was designed to compare thymidylate synthase (TS) genotype, mRNA and protein levels in primary colorectal adenocarcinoma, and to examine the correlation between microsatellite instability (MSI) and TS expression. The TS genotype of 68 patients with colorectal cancer was determined by polymerase chain reaction (PCR) and restriction fragment length polymorphism analysis in peripheral blood mononuclear cells and tumour tissue. The TS mRNA levels in tumour tissue were measured by reverse-transcription PCR, and TS protein levels and MSI status were assessed using immunohistochemistry. Significantly higher mRNA and protein levels were observed in patients with the TS 3R/3R versus the 2R/2R and 2R/3R genotypes. There was no correlation between TS single nucleotide polymorphism and TS expression. Individuals homozygous for the six base-pair insertion in the 3'-untranslated region had significantly higher TS mRNA levels than heterozygous and homozygous wild type individuals. The TS mRNA and protein levels were significantly higher in microsatellite unstable tumours compared with microsatellite stable tumours. There was a significant association between the number of TS enhancer region repeats (in blood) and intratumoural TS mRNA and protein levels. A larger case series investigating the role of TS gene polymorphisms as predictors of sensitivity to 5-fluorouracil-based chemotherapy is required.

Implication of CDK Inhibitors p21 and p27 in the Differentiation of HL-60 Cells

All-trans retinoic acid (ATRA) differentiates HL-60 cells into granulocyte-like cells and cellular proliferation is repressed markedly along with the morphological and physiological changes specific for cellular differentiation. To elucidate the implication of cyclin-dependent kinase (CDK) inhibitors during differentiation, we examined the expression of CDK inhibitors during the differentiation of HL-60 cells. The expression of p21 and p27 among the CDK inhibitors we examined increased during the differentiation induced with ATRA. Then, we established stable transformants of HL-60 cells expressing antisense RNA for p21 and p27 and examined the ability of these cells to differentiate into granulocyte-like cells. The extents of fully differentiated HL-60 cells transfected with genes for antisense RNA of p21 and p27 were only 53% and 60%, respectively, whereas 90% of the parental HL-60 cells differentiated by the ATRA treatment. These results suggest that increased expression of CDK inhibitors, p21 and p27, is necessary for the differentiation of HL-60 cells induced with ATRA.

Functional polymorphism of the thymidylate synthase gene in colorectal cancer accompanied by frequent loss of heterozygosity

The thymidylate synthase (TS) gene has a polymorphic repeated sequence in its 5'-untranslated region. The repeat length is associated with TS protein expression, which suggests that we may be able to predict the efficacy of 5-fluorouracil (5-FU)-based chemotherapy from a patient's TS genotype determined through analysis of normal tissue obtained non-invasively. However, it is not yet elucidated whether the TS genotype is identical in tumor and normal tissue. In this study, we investigated the TS genotype in 151 matched tumor and normal DNA samples isolated from colorectal cancer and adjacent normal tissues by PCR analysis. The results showed that TS genotypes are identical in normal and tumor tissues of homozygous individuals, suggesting that the repeat sequence is stable through carcinogenesis. However, in heterozygous samples, an imbalance between the 2R and 3R alleles in the tumor DNA was frequently observed, suggesting loss of heterozygosity (LOH) at the TS locus. Detailed LOH analysis revealed that 62% (31 of 50) of 2R/3R-heterozygous samples had LOH. Frequent LOH at the TS locus was confirmed by RT-PCR of TS mRNA and microsatellite analysis using the marker D18S59, located on 18p11.3. There was no difference in the expressions of TS mRNA and TS protein between LOH and non-LOH samples. However, when the heterozygous genotype bearing LOH was subdivided according to the number of repeats, the cancer tissue with 2R/loss genotype expressed a significantly lower level of TS protein than did that with 3R/loss genotype. The results suggest that the difference in TS genotype between tumor and normal tissue due to LOH should be considered when the genotype is analyzed with normal tissue, such as peripheral blood cells, because it is important for TS protein expression.