Detection of APC mutations by a yeast-based protein truncation test (YPTT)

APC gene mutations play a role in the initiation step of colorectal carcinogenesis in both familial adenomatous polyposis (FAP) and non-FAP patients. Almost all of the APC mutations are nonsense or frameshift mutations, which truncate the APC protein and are thought to inactivate normal APC function. We show a novel method for detecting nonsense and frameshift APC gene mutations by using Saccharomyces cerevisiae. Polymerase chain reaction (PCR)-amplified APC fragments are cloned directly into yeast expression vectors in vivo, and the yeast expresses a hemagglutinin epitope (HA)-tagged APC peptide. When an APC fragment contains a nonsense or frameshift mutation, HA-tagged truncating APC peptide can be detected by Western blotting using an anti-HA antibody. We identified both germ-line and somatic APC mutations in patients with FAP and non-FAP colorectal tumors, respectively. This method, called the yeast-based protein truncation test (YPTT), is simple and fairly cheap, and it can be applied to any genes that are inactivated by protein truncating mutations.

Screening the p53 status of human cell lines using a yeast functional assay

We have screened the p53 status of 156 human cell lines, including 142 tumor cell lines from 27 different tumor types and 14 cell lines from normal tissues by using functional analysis of separated alleles in yeast. This assay enables us to score wild-type p53 expression on the basis of the ability of expressed p53 to transactivate the reporter gene HIS3 via the p53-responsive GAL1 promotor in Saccharomyces cerevisiae. Of 142 tumor cell lines, at least 104 lines (73.2%) were found to express the mutated p53 gene: 94 lines (66.2%) were mutated in both alleles, three lines (2.1%) were heterozygous, and no p53 cDNA was amplified from seven lines (4.9%). Of the 14 cell lines originating from normal tissues, all the transformed or immortalized cell lines expressed mutant p53 only. Yeast cells expressing mutant p53 derived from 94 cell lines were analyzed for temperature-sensitive growth. p53 cDNA from eight cell lines showed p53-dependent temperature-sensitive growth, growing at 30 degrees C but not at 37 degrees C. Four temperature-sensitive p53 mutations were isolated: CAT-->CGT at codon 214 (H214R), TAC-->TGC at codon 234 (Y234C), GTG-->ATG at codon 272 (V272M), and GAG-->AAG (E285K). Functionally wild-type p53 was detected in 38 tumor cell lines (26.8%) and all of the diploid fibroblasts at early and late population doubling levels. These results strongly support the previous findings that p53 inactivation is one of the most frequent genetic events that occurs during carcinogenesis and immortalization.

Detection of heterozygous truncating mutations in the BRCA1 and APC genes by using a rapid screening assay in yeast

The detection of inactivating mutations in tumor suppressor genes is critical to their characterization, as well as to the development of diagnostic testing. Most approaches for mutational screening of germ-line specimens are complicated by the fact that mutations are heterozygous and that missense mutations are difficult to interpret in the absence of information about protein function. We describe a novel method using Saccharomyces cerevisiae for detecting protein-truncating mutations in any gene of interest. The PCR-amplified coding sequence is inserted by homologous recombination into a yeast URA3 fusion protein, and transformants are assayed for growth in the absence of uracil. The high efficiency of homologous recombination in yeast ensures that both alleles are represented among transformants and achieves separation of alleles, which facilitates subsequent nucleotide sequencing of the mutated transcript. The specificity of translational initiation of the URA3 gene leads to minimal enzymatic activity in transformants harboring an inserted stop codon, and hence to reliable distinction between specimens with wild-type alleles and those with a heterozygous truncating mutation. This yeast-based stop codon assay accurately detects heterozygous truncating mutations in the BRCA1 gene in patients with early onset of breast cancer and in the APC gene in patients with familial adenomatous polyposis. This approach offers a rapid and reliable method for genetic diagnosis in individuals at high risk for germ-line mutations in cancer susceptibility genes.

Oligomerization is not essential for growth suppression by p53 in p53-deficient osteosarcoma Saos-2 cells

The carboxy-terminal portion of the p53 protein contains the tetramerization domain, and the introduction of multiple missense mutations in this domain disrupts the formation of p53 tetramers, resulting in the production of dimeric or monomeric forms of p53. It has recently been shown that a single missense or nonsense mutation in this domain affects the functional properties of p53 both in yeast and in mammalian cells. In this study, we tested the oligomerization of p53 with mutations in the oligomerization domain, when expressed in a human osteosarcoma cell line, Saos-2, in vivo. We found that single point mutations, including two missense and two nonsense mutations, in the alpha-helix of the oligomerization domain disrupted the oligomerization of p53, but that p53 still retained its ability to inhibit colony formation of cells to some degree. These results suggest that oligomerization and the carboxy-terminal basic domain are not prerequisite for p53-dependent tumor suppression, and this may explain why few of the tumor-derived p53 mutations that have been examined so far are carboxy-terminal mutations.

[Functional screening of p53 status in tumor cells using Saccharomyces cerevisiae]

We have detected both germ-line and somatic p53 mutations in lymphocytes, cell lines and tumor tissues using a functional analysis of p53 tumor suppressor gene based on yeast transcription assay. Through our screening projects of the p53 gene, a number of missense p53 mutations were identified as loss-of-function mutations. This method, previously termed FASAY, is rapid, sensitive, less-expensive and can be automated for screening both somatic and germ-line p53 mutations.

Enhancement of chemotherapeutic effects with focused shock waves: extracorporeal shock wave chemotherapy (ESWC)

The effects of shock waves in combination with various anti-cancer agents i.e. Bleomycin (BLM), Cisplatin (CDDP) and 5-fluorouracil (5-FU) on tumor cells suspended in media containing these agents were examined. GCIY cells derived from human gastric cancer and LS 174T and SW480 cells derived from human colon cancers were used for in vitro experiments; GCIY and SW480 cells were also transplanted into nude mice for in vivo study. It was only with BLM that enhancement was evident in all three cell lines, with a degree of chemotherapeutic enhancement proportional to the amount of shock wave energy applied. Ladder formation of DNA in GCIY cells was observed only when treated with both BLM and shock waves in combination. When SW480 and GCIY cells transplanted into the backs of nude mice were treated with a combination of intravenously (i.v.) injected BLM and regional exposure to shock waves, a significant enhancement of chemotherapeutic effects was observed in terms of the tumor growth curve.

Enhancement of anticoagulant action by warfarin-benzbromarone interaction

To investigate the interaction between warfarin potassium and benzbromarone, administration of benzbromarone to patients receiving long-term treatment with both drugs was discontinued for 1 week and then resumed, and the resulting changes in the coagulation system were examined. Thrombotest value, activity of coagulation factors II and VIII, concentration of protein induced by vitamin K absence or antagonist-II (PIVKA-II), total plasma concentration of warfarin, and free warfarin concentration were measured during the period of concurrent administration of the two drugs, 1 week after discontinuation of benzbromarone, and after resumption of benzbromarone administration. After administration of benzbromarone had been discontinued for 1 week, the thrombotest value and factor II activity rose significantly whereas PIVKA-II activity dropped significantly compared with corresponding levels before discontinuation, but these parameters tended to revert to the previously maintained levels after resumption of benzbromarone treatment. Activity of the vitamin K-independent factor VIII displayed almost no changes, however. Total plasma warfarin concentration also decreased significantly, and free warfarin concentration was nearly unchanged. These results verified that the anticoagulant action of warfarin is enhanced by concurrent administration of benzbromarone. Accordingly, adequate consideration must be devoted to the prevention of grave hemorrhagic tendencies when these two drugs are administered concurrently.

[Genetic alterations of human colorectal cancer]

Genetic alterations of several oncogenes and tumor suppressor genes are associated with human colorectal carcinogenesis. Especially in mutations, the K-ras, p53, APC and DCC gene frequently occurred, and these gene alterations seem to have important roles in colorectal carcinogenesis. We investigated 28 human colon cancer specimens obtained from surgery and five human colon cancer cell lines by PCR-SSCP assay, PCR-OSH assay, RT-PCR or sequencing method. Forty percent of cancers from surgical specimens had Ki-ras 2 (codon 12/13), p53 (Exon 5-8), APC (MCR) gene mutations, and fifty-seven percent of them had lower expression of DCC gene that of normal matched colon mucosa of the same patient. G to A transition was the most frequent in K-ras mutational spectrum in this case; 25% of patients had both k-ras and p53 gene point mutations. Form the results, we concluded that it in colorectal carcinogenesis for both K-ras and p53 gene point mutations might not necessary occur.

Comparison of adrenal functions in kidney transplant recipients with different long-term immunosuppressive treatments--prednisolone and azathioprine versus prednisolone and cyclosporine

Adverse effects of cyclosporine on the adrenal cortex have been documented in animal experiments, but nothing has been reported in human subjects. Endogenous cortisol in peripheral blood was monitored for three years after transplantation, with 30 kidney recipients on two different immunosuppressive treatments. In the azathioprine group, 16 patients were treated with coadministration of prednisolone at an initial dose of 120 mg/day. In the cyclosporine group, 14 patients were also treated with prednisolone, using an initial dose of 60 mg per day. Short ACTH stimulation tests were performed to reconfirm the results obtained by basal cortisol monitoring. During the first year following transplant, cortisol concentrations in the cyclosporine group were higher, though not significantly so, than those in the azathioprine group, in accordance with cumulative amounts of prednisolone administered. At three years, however, the mean cortisol concentrations in the azathioprine group were 2-3 times higher than those in the cyclosporine group (P < 0.05). All patients in the azathioprine group responded well to ACTH, whereas 4 patients out of 14 in the cyclosporine group showed continuous severe suppression without considerable response to ACTH (P < 0.01). In conclusion, we would like to suggest that adrenocortical toxicity of long-term cyclosporine use may appear one year after transplant, resulting in chronic suppression of the adrenal cortex, and, accordingly, difficulty in further reduction of prednisolone use.

Suppression of endogenous cortisol for evaluating pharmacodynamics of prednisolone in early allograft rejection in renal transplantation

Concentrations of endogenous cortisol were examined in 34 kidney-transplant recipients by improved "high-performance" liquid chromatography. Ten recipients were treated with prednisolone and azathioprine, the others with prednisolone and cyclosporine. Peripheral serum samples were collected just before transplantation, daily for two weeks after the transplant, weekly until discharge for about two months, and then monthly or occasionally. Mean (+/- SD) cortisol concentrations, initially 145 +/- 87 micrograms/L, decreased immediately to 5.93 +/- 5.11 micrograms/L after transplant, remained at almost these same values for two months, and then swiftly increased to 51 +/- 59 micrograms/L by 1000 days. Cortisol concentrations within the period characterized by a cumulative dose of prednisolone at 300-700 mg were correlated significantly with the presence or absence of acute allograft rejection; patients with cortisol greater than 4 micrograms/L had a higher risk of rejection. The majority of stable patients showed cortisol concentrations between 1 and 4 micrograms/L throughout the cumulative prednisolone period characterized above. Concentrations less than 1 microgram/L after high-dose administration of methylprednisolone were accompanied by severe lung infection. We conclude that suppressed concentrations of endogenous cortisol, as assessed by highly specific HPLC, might provide a basis for predicting the therapeutic efficacy and adverse effects of prednisolone.

Suppression of endogenous cortisol for evaluating pharmacodynamics of prednisolone in early allograft rejection in renal transplantation

Concentrations of endogenous cortisol were examined in 34 kidney-transplant recipients by improved "high-performance" liquid chromatography. Ten recipients were treated with prednisolone and azathioprine, the others with prednisolone and cyclosporine. Peripheral serum samples were collected just before transplantation, daily for two weeks after the transplant, weekly until discharge for about two months, and then monthly or occasionally. Mean (+/- SD) cortisol concentrations, initially 145 +/- 87 micrograms/L, decreased immediately to 5.93 +/- 5.11 micrograms/L after transplant, remained at almost these same values for two months, and then swiftly increased to 51 +/- 59 micrograms/L by 1000 days. Cortisol concentrations within the period characterized by a cumulative dose of prednisolone at 300-700 mg were correlated significantly with the presence or absence of acute allograft rejection; patients with cortisol greater than 4 micrograms/L had a higher risk of rejection. The majority of stable patients showed cortisol concentrations between 1 and 4 micrograms/L throughout the cumulative prednisolone period characterized above. Concentrations less than 1 microgram/L after high-dose administration of methylprednisolone were accompanied by severe lung infection. We conclude that suppressed concentrations of endogenous cortisol, as assessed by highly specific HPLC, might provide a basis for predicting the therapeutic efficacy and adverse effects of prednisolone.