Desensitization and sensitization of cells to fluoropyrimidines with different antisenses directed against thymidylate synthase messenger RNA

Previous studies have shown that the cytotoxicity of fluoropyrimidines is mediated, in large part, by inhibition of the enzyme thymidylate synthase (TS). The aim of this study was to determine whether the chemosensitivity of human cancer cells to fluoropyrimidines could be increased by decreasing TS expression with antisense oligodeoxyribonucleotides (ODNs). ODNs (18-mers) targeted at the AUG translational initiation site of TS mRNA inhibited translation in a sequence- and dose-dependent manner in a rabbit reticulocyte lysate in vitro translation system. Treatment of human colon cancer HT-29 cells with antisense ODNs decreased TS catalytic activity in the cells in a dose-dependent manner over a short period, but the longer-term effect of the TS antisense ODN treatment was actually to increase the amount of TS in the cells and to decrease their sensitivity to 5-fluoro-2'-deoxyuridine (FdUrd). However, when human nasopharyngeal cancer KB31 cells were transfected with a plasmid (pHaMAGRP) construct containing the TS antisense fragment (+ 1 to + 422) under the control of a glucose-regulated promoter, the expression of both TS protein and TS catalytic activity was decreased by nearly 30% (P = 0.014), and sensitivity of these cells to FdUrd was enhanced by approximately 8-fold (P = 0.021). No changes in the levels of expression of TS protein or FdUrd-associated cytotoxicity were observed in control, vector-transfected cells. No change was observed in the sensitivity of transfected cells toward either cisplatin or Adriamycin. These results show that the level of expression of TS in human malignant cells can be down-regulated with antisense TS RNA, and their sensitivity to fluoropyrimidines can, thereby, be increased.

p53 point mutations and thymidylate synthase messenger RNA levels in disseminated colorectal cancer: an analysis of response and survival

Recent studies suggest that there may be a strong correlation between the p53 status of a tumor and a patient's response to chemotherapy. Therefore, we determined p53 status in 36 patients with disseminated colorectal cancer by cDNA sequencing and immunohistochemical staining, as well as by the gene expression level of thymidylate synthase (TS), the target enzyme of 5-fluorouracil (5-FU), by reverse transcription-PCR. Ten patients (28%) experienced a clinical response to 5-FU chemotherapy. Overall, TS expression and response to chemotherapy were associated: 9 of 18 (50%) patients with TS < or = 3.0 x 10(-3) responded, compared to 1 of 18 (6%) patients with TS > 3.0 x 10(-3) (P = 0.003). p53 mutations were found in 21 of 36 patients (58%) using cDNA cycle sequencing, and p53 protein overexpression was found in 20 of 32 patients (62%) using immunohistochemistry staining. Overall p53 status and response to chemotherapy were associated: 5 of 10 (50%) patients with wild-type p53 or negative p53 staining experienced a response, but only 5 of 26 (19%) patients with mutant p53 or p53 overexpression responded. TS expression, but not expression of p53, was significantly associated with overall survival (P = 0.002). Patients with wild-type p53 had significantly lower TS levels compared to patients with mutated p53 (P = 0.044). In this study, we also present data linking specific p53 point mutations to TS expression levels and resistance to 5-FU. Although the number of patients is relatively small, these results identify p53 status and TS gene expression as associated with response in disseminated colorectal cancer; independent studies are needed to confirm these findings and to provide information leading to a better understanding of the role of 5-FU-based chemotherapy in the treatment of colorectal cancer.

p53 and thymidylate synthase expression in untreated stage II colon cancer: associations with recurrence, survival, and site

We initiated a retrospective study to determine whether p53 status and thymidylate synthase (TS) protein expression in primary colon tumors influence recurrence and survival for patients with stage II colon cancer. Tumor specimens from 45 consecutive untreated patients with stage II colon cancer were examined for p53 and TS protein expression using immunohistochemistry. The median follow-up was 5.1 years. Eighteen patients had left-sided tumors, and 27 had right-sided tumors. Fourteen of 45 patients (31%) developed recurrence. p53 overexpression was detected in the tumors of 18 patients (40%); 10 patients (55%) with p53 overexpression recurred; and 4 of 27 (15%) without evidence of p53 overexpression recurred (P = 0.002). High TS expression was detected in the tumors of 16 patients (36%): 8 patients (50%) with high TS expression recurred, and 6 patients (21%) with low TS expression recurred (P = 0.027). Patients with p53 overexpression had a significantly poorer survival than did those patients without p53 overexpression (P < 0.001). High TS expression was associated with poor survival (P = 0.004). p53 overexpression and high TS expression were significantly associated with left-sided tumors (P = 0.003 and P = 0.022). Thirteen of 16 patients (81%) with high TS expression also overexpressed p53, and 24 of 29 patients (81%) with low TS expression did not manifest p53 overexpression (P < 0.001). p53 and TS expression in primary stage II colon cancer are associated and appear to influence recurrence and survival. In this pilot study, left-sided tumors demonstrate significantly more p53 overexpression and significantly higher TS expression than do right-sided tumors, which may explain the significantly poorer survival for patients with left-sided tumors.

Restoration of wild-type p53 activity in p53-null HL-60 cells confers multidrug sensitivity

HL-60 cells that stably express transfected wild-type (wt) p53 were used to determine whether restoration of wt p53 increased the chemosensitivity of cells that normally lack p53 activity. The wt p53 HL-60 transfectants (SN3 cells) were more sensitive than the parental (S) cells to a number of common anticancer drugs representing various mechanisms of action, whereas HL-60 cells transfected with p53 genes mutated at codons 248 and 143 were not sensitized. The sensitization ratio due to the transfected wt p53 varied from about 2-fold for cisplatin to over 50-fold for thymidine. Cells treated with the thymidylate synthase inhibitor 5-fluoro-2'-deoxyuridine (FdUrd) were used to study changes in various p53-associated gene expressions. A higher percentage of apoptotic cells among the SN3 cells was observed than among the S cells at each concentration of FdUrd. The S cells had undetectable levels of bax and high levels of bcl-2, whereas the SN3 cells had undetectable levels of bcl-2 levels and appreciable basal levels of bax. After FdUrd treatment of SN3 cells, both p53 and bax levels increased, but the induction of bax was faster than that of p53 and paralleled the appearance of apoptotic DNA laddering. FdUrd treatment induced p21 expression and increased the G1 fraction of the SN3 cells but did not induce p21 or change the phase distribution in the S cells. FdUrd treatment also induced the expression and phosphorylation of cyclin D1 in the SN3 cells but not in the S cells. These results show that transfected wt p53 confers multidrug sensitivity to HL-60 cells by re-adjustment of the expressions of apoptosis genes and displays other properties characteristic of endogenously originated wt p53.

Intercellular communication mediates the bystander effect during herpes simplex thymidine kinase/ganciclovir-based gene therapy of human gastrointestinal tumor cells

A bystander effect is described when nontransduced or genetically unmodified cells are killed during death of genetically modified tumor cells transduced with a suicide gene. The "bystander effect" greatly enhances the efficacy of the herpes simplex virus-thymidine kinase/ganciclovir (HSV-TK/GCV) gene therapy approach for cancer. The mechanism of the bystander effect is controversial. In this study, we examined the role of intercellular gap junction communication (GJIC) for the bystander effect in human gastrointestinal tumor cells. Our results show that the extent of the bystander effect varied amongst the tumor cell lines; pancreatic cancer cells BXPC-3 exhibited excellent bystander effects in vitro and in vivo studies whereas other gastrointestinal tumor cell lines such as pancreatic cancer cells MIAPACA-2, and colon cancer cells HT-29 showed poor bystander effects. Bystander effects were only found in the presence of cell-to-cell contact. The extent of the bystander effect was independent of the level of HSV-TK activity in the transduced tumor cells and was correlated with GJIC as demonstrated by an in vitro dye-transfer assay. Expression of the mRNA levels of gap junction protein connexin 43 was 8- to 26-fold or greater and connexin 26 gene expression was 2- to 229-fold greater in BXPC-3 cells compared to HT-29, MIAPACA-2, and PANC3 cells. Our results suggest that intercellular communication is essential for the bystander effect. The correlation between GJIC and the extent of the bystander effect suggest a role for GJIC in mediating the bystander effect. Analysis of tumors for GJIC or expression of gap junction proteins may identify the subset of patients suitable for gene therapy with the HSV-TK/GCV approach.

ERCC1 mRNA levels complement thymidylate synthase mRNA levels in predicting response and survival for gastric cancer patients receiving combination cisplatin and fluorouracil chemotherapy

PURPOSE

We have previously shown that relative thymidylate synthase (TS) mRNA levels in primary gastric adenocarcinomas treated with fluorouracil (5-FU) and cisplatin are inversely associated with response and survival. This is a presumed function of TS as a target for 5-FU activity. We now test the hypotheses that the relative mRNA level of the excision repair cross-complementing (ERCC1) gene is inversely associated with response and survival as an independent function of cisplatin efficacy.

PATIENTS AND METHODS

Patients had intact, untreated, primary gastric adenocarcinoma cancer and were evaluated for eligibility on a preoperative cisplatin infusion-5-FU protocol. cDNA, derived from primary gastric tumors before chemotherapy, was used to determine ERCC1 mRNA levels, expressed as the ratio of polymerase chain reaction (PCR) product of the ERCC1 gene and the beta-actin gene.

RESULTS

The median ERCC1 mRNA level from 38 primary gastric cancers (33 assessable for response) was 5.8 x 10(-3) (range, 1.8 x 10(-3) to 19.5 x 10(-3)). Of 17 responding patients, 13 (76%) were less than or equal to 5.8 x 10(-3) and four were greater than 5.8 x 10(-3) (P = .003). The median survival for patients with ERCC1 mRNA levels less than or equal to 5.8 x 10(-3) has not been reached, whereas for those greater than 5.8 x 10(-3) it was 5.4 months (P = .034). The median TS mRNA level, 3.7 x 10(-3) (range, 0.9 to 18.9) also segregated responsive versus resistant tumors (P = .024). With both ERCC1 and TS mRNA levels below their medians, 11 of 13 patients (85%) responded; with both ERCC1 and TS mRNA levels above their medians, two of 10 patients (20%) responded (P = .003).

CONCLUSION

Considered separately, either ERCC1 or TS mRNA levels in a primary gastric adenocarcinoma has a statistically significant relationship to response. ERCC1 mRNA levels have a statistically significant association with survival; in this cohort TS mRNA levels did not reach statistically significant association with survival as in our previous publication. Whether these molecular parameters are independent of each other as predictors of outcome remains to be determined.

Quantitation of intratumoral thymidylate synthase expression predicts for disseminated colorectal cancer response and resistance to protracted-infusion fluorouracil and weekly leucovorin

PURPOSE

Response rates to fluorouracil (5-FU)-based therapy remain low. As new, active agents are being tested, information regarding specific intratumoral genetic determinants of chemotherapy sensitivity or resistance can be used to plan therapy rationally. Intratumoral thymidylate synthase (TS) quantitation may be among the most important determinants of sensitivity or resistance to 5-FU.

MATERIALS AND METHODS

Forty-six disseminated colorectal cancer patients had measurable tumor biopsies for polymerase chain reaction (PCR)-based determination of TS mRNA pretreatment. Protracted infusion of 5-FU 200 mg/m2/d for 21 days with weekly intravenous leucovorin 20 mg/m2 each cycle was given. After two cycles, responses were evaluated. Response data were correlated with independently determined intratumoral ratios of TS/beta-actin mRNA for each patient.

RESULTS

TS/beta-actin ratios were successfully obtained for 42 patients (91%). TS/beta-actin ratios ranged from 0.3 x 10(-3) to 18.2 x 10(-3) (median, 3.5 x 10[-3]). Twelve patients (26%) responded to treatment (median TS/beta-actin ratio, 1.7 x 10[+3]). Thirty-four patients did not respond (median TS/beta-actin ratio, 5.6 x 10[-3]). No patient with a TS mRNA level greater than 4.1 x 10(-3) responded. The median TS/beta-actin ratio (3.5 x 10[-3]) significantly segregated responders from nonresponders (P = .001). Median survival for patients with TS/beta-actin ratios < or = 3.5 x 10(-3) was 13.6 months; for patients with TS/beta-actin ratios greater than 3.5 x 10(-3), it was 8.2 months (P = .02).

CONCLUSION

For this cohort, the intratumoral TS/beta-actin ratio had a statistically significant association with response and survival. This relationship for other 5-FU schedules remains unknown. Confirmation of these data in a larger patient population could lead to determination of therapy for disseminated colorectal cancer based on a specific intratumoral molecular parameter.

High frequency of simultaneous loss of p16 and p16beta gene expression in squamous cell carcinoma of the esophagus but not in adenocarcinoma of the esophagus or stomach

Quantitative reverse transcription PCR (RT-PCR) was used to measure gene expressions (relative mRNA levels) of p16 and the alternate transcript pl6beta in esophageal and gastric tumors. p16 gene expression was undetectable in 13 of 25 esophageal squamous cell carcinomas. In 11 of these tumors, pl6beta was simultaneously missing whereas two of the pl6-deficient tumors still expressed p16beta. Among 34 esophageal adenocarcinomas and 11 gastric adenocarcinomas, only one tumor lacked p16 expression and all tumors expressed p16beta. p16 sequences were not detectable by PCR in genomic DNA from tumors lacking both p16 and p16beta mRNA, suggesting that the simultaneous loss of both gene expressions resulted from homozygous genomic deletion of the p16 gene. However, DNA from tumors that lacked p16 mRNA but expressed pl6beta did contain the p16 gene, consistent with loss of p16 expression in these tumors by transcriptional suppression. No point mutations in p16 cDNA were detected among 12 that were sequenced, but one p16 cDNA from a squamous cell carcinoma had a 19-base deletion, possibly indicating a splice-site mutation. Among those tumors that expressed p16 mRNA, the gene expression values of both p16 and pl6beta varied over a wide range. In some cases, p16 expression was detectable but low, suggesting that down-regulation of p16 expression may be used in some cases to achieve the funtional equivalent of gene deletion or transcriptional silencing. These results demonstrate that p16 expression patterns differ based on tumor histology and origin. Homozygous deletion of p16 appears to be common in esophageal squamous cell carcinomas but in adenocarcinomas, both gene deletion and transcriptional silencing of p16 were infrequent.

Thymidylate synthase is a predictor for response and resistance in hepatic artery infusion chemotherapy

The value of intratumoral thymidylate synthase (TS) quantitation as a predictive parameter for hepatic artery infusion (HAI) chemotherapy in patients with colorectal liver metastases was investigated. Relative TS mRNA levels were determined in 29 tumor samples using a quantitative RT-PCR amplification method. The median level of expression was 3.0 x 10(-3) (no units) and varied considerably among the tumors over a range of 135-fold. Patients with low TS levels were 4.1-fold more likely to respond (P < 0.03) compared to patients with high TS levels. Our results indicate that TS quantitation is a valuable predictive marker for tumor response to HAI therapy.

Thymidylate synthase mRNA level in adenocarcinoma of the stomach: a predictor for primary tumor response and overall survival

PURPOSE

We tested the hypothesis that polymerase chain reaction (PCR) quantitation of the enzyme thymidylate synthase (TS) within a primary adenocarcinoma of the stomach, has an inverse relationship to response and survival for patients who receive fluorouracil (5FU)-based chemotherapy.

PATIENTS AND METHODS

Before systemic chemotherapy, the genetic expression of TS (TSmRNA level) was determined using a PCR method. Gene expression was calculated by determining the ratio between the amount of radiolabeled PCR product with the linear amplification range of the TS gene and the beta-actin gene. Chemotherapy consisted of two cycles of protracted infusion (PI) 5FU 200 mg/m2/d administered for 3 weeks with leucovorin 20 mg/m2/w. Cisplatin 100 mg/m2 was administered on day 1.

RESULTS

Sixty-five patients with primary gastric cancer had a median TS mRNA level of 4.6 x 10(-3) (range, 0.9 to 20.1 x 10(-3)). Thirty-five percent of patients had measurable responses in their primary tumors. The mean gastric cancer TSmRNA level in responding and resistant patients is statistically significant (P < .001). The median survival time was 43+ months for treated patients with TSmRNA levels less than the median and 6 months for those with TS m-RNA levels greater than the median (P = .003).

CONCLUSION

The genetic expression of TS (TSmRNA level) influences response to 5FU-based chemotherapy and survival for a cohort of patients with primary gastric cancer. Confirmation of these data could lead to therapeutic decisions based on specific molecular properties within a tumor.

Transfection of wild-type but not mutant p53 induces early monocytic differentiation in HL60 cells and increases their sensitivity to stress

HL60 cells, which lack the p53 gene due to a deletion, were used as an in vitro model system to study the effect of wild-type p53 gene expression on hematopoietic differentiation. We transfected HL60 cells with wild-type p53 and two mutant p53 cDNAs encoding the Val to Ala mutation at codon 143 and the Arg to Trp mutation at codon 248. Flow cytometry, growth, and cytochemical analysis for alpha-napthyl butyrate esterase activity and nitroblue tetrazolium reduction indicated that wild-type p53 but not mutant p53 induced early monocytic differentiation in the transfected HL60 cells without terminal growth arrest. The wild-type p53 transfectants did not differentiate along the granulocytic pathway, even when induced with 1.25% DMSO for 6 days; rather, these cells resembled monocytic cells, confirming that wild-type p53 transfection caused these cells to become committed to differentiate along the monocytic pathway. HL60 cells transfected with wild-type p53 were more sensitive to stress, such as growth in serum-depleted medium and exposure to a chemotherapeutic agent, etoposide.

Identification of mutations by RNA conformational polymorphism "bar code" analysis

DNA single-strand conformational polymorphism (SSCP) analysis is widely used for detection of point mutations in clinical specimens. Performing SSCP analysis with cRNA instead of DNA has been shown to improve mutation detection frequency. RNA can exist in numerous meta-stable conformations, which appear as patterns of bands on nondenaturing electrophoresis gels. Single base mutations can cause not only mobility shifts of major bands, but also loss of some conformations and appearance of new conformations. Unique RNA SSCP patterns associated with specific base sequences in many cases allow visual identification of point mutations. However, in some cases, the RNA SSCP pattern of a single base change in a sequence is not sufficiently different for a positive identification of the mutation. Improvement in the detection capability of RNA SSCP was obtained by adding 3'-deoxynucleotides to the transcription reaction. The presence of chain-terminating nucleotides in the transcription reaction formed numerous new RNA fragments, thereby generating complex band patterns ("bar codes") unique to each RNA sequence. This method was applied to analyzing p53 mutations in patients with colon cancer.

Effects of cerebral TRH on intestinal water transport: role of vagal, muscarinic, and VIP pathways

Thyrotropin-releasing hormone (TRH) is a central nervous system (CNS) transmitter that stimulates various gastrointestinal secretory and motor processes by increasing vagal outflow. In this study, the CNS effects of TRH on ileal and jejunal water transport were examined in awake rats and dogs, respectively. Cerebral but not intravenous TRH (0.1-5.0 nmol/kg) significantly (P < 0.01) reversed net water absorption from approximately 30 microliters.cm-1.h-1 in rats and 300 microliters.cm-1.h-1 in dogs toward net water secretion of 60 and 600 microliters.cm-1.h-1, respectively. Truncal vagotomy and ganglionic blockade with chlorisondamine completely abolished this stimulatory effect of cerebral TRH, whereas adrenalectomy, hypophysectomy, noradrenergic and opiate blockade, and inhibition of prostaglandin and nitric oxide synthesis did not. Atropine methylnitrate significantly (P < 0.05) attenuated the stimulatory response produced by TRH by approximately 30%. Intravenous infusion of the vasoactive intestinal peptide (VIP) receptor antagonist, [4Cl-D-Phe6, Leu17]VIP (0.05-5.0 mumol.kg-1.h-1), significantly (P < 0.01) inhibited the stimulatory response of TRH by approximately 60%. Pretreatment of the animals with both atropine and the VIP antagonist completely abolished ileal and jejunal water secretion stimulated by cerebral TRH. These results indicate that 1) TRH acts within the CNS to stimulate net ileal and jejunal water secretion in rats and dogs, respectively; 2) these actions are mediated by vagal pathways; and 3) stimulation of intestinal secretion by cerebral TRH is primarily mediated by a VIP-sensitive mechanism and, in part, by a muscarinic mechanism.

Quantitation of intratumoral thymidylate synthase expression predicts for resistance to protracted infusion of 5-fluorouracil and weekly leucovorin in disseminated colorectal cancers: preliminary report from an ongoing trial

A clinical trial for patients with measurable, disseminated colorectal cancer is being conducted to determine: (1) if intratumoral expression of thymidylate synthase (TS) affects response to protracted-infusion 5-fluorouracil (5FU); and (2) whether intratumoral expression of TS increases when clinical resistance is found after response to 5-FU. Polymerase chain reaction technology is employed to determine TS expression. Using beta-actin as an internal standard, TS expressions for 26 patients range from 0.5 x 10(-3) to 22.6 x 10(-3). Currently, 22 patients are evaluable for response and TS quantitation of their measurable tumour. 8 patients (36%) have had partial responses; 3 responding patients had been previously treated with 5-FU. A strong statistical association between TS expression and resistance to therapy has been found (P = 0.004). No patient with TS expression of 4.0 x 10(-3) or greater has responded. On average, patients previously treated with 5-FU have slightly higher levels of TS expression in their measurable tumours (P = 0.4). Whether responding patients will develop increased expressions of TS upon clinical progression of their cancer remains to be determined. Confirmation of these results in a larger cohort could lead to a scientific rationale for deciding upon specific therapy for patients with disseminated colorectal cancers.

Thymidylate synthase gene and protein expression correlate and are associated with response to 5-fluorouracil in human colorectal and gastric tumors

Thymidylate synthase (TS) is the target enzyme for 5-fluorouracil (5-FU). We have correlated TS protein and gene expression with the response in patients with colorectal (n = 9) and gastric cancer (n = 12) treated with infusional 5-FU plus leucovorin (LV) or infusional 5-FU/LV and cisplatin, respectively. TS protein expression was analyzed by Western blot using TS106 monoclonal antibody and densitometry scanning. TS gene expression was measured by PCR analysis using beta-actin as an internal standard and expressed as a TS:beta-actin mRNA ratio. A close linear relationship was noted between TS protein expression and TS gene expression (r2 = 0.60) for the 21 tumor samples analyzed. TS immunohistochemical staining on 15 of the 21 samples revealed that the TS staining intensity correlated closely with TS protein and mRNA expression. In two biopsy samples, TS protein levels and TS gene expression did not correlate; however, one of these exhibited a focal TS staining pattern. Both the TS protein level and TS gene expression were significantly associated with response to 5-FU-based therapy. Patients with responsive disease had a mean TS protein level of 0.17 +/- 0.03 arbitrary units (range, 0.05 to 0.38), whereas in patients whose tumors did not respond, the mean TS protein level was significantly higher 0.60 +/- 0.09 (range, 0.06 to 1.01; P < 0.01). A similar pattern was noted with TS gene expression. In patients with responsive disease, the mean TS:beta-actin gene ratio was 1.36 +/- 0.3 (range, 0.5-3.3 x 10(-3). In contrast, biopsies from patients with unresponsive disease had a mean TS:beta-actin gene ratio of 15.4 +/- 2.6 x 10(-3) (range, 2.7-35.9; P < 0.01). TS protein and TS mRNA expression are highly correlated, and each predict for response to 5-FU/LV-based chemotherapy in patients with colorectal and gastric cancer.

Gene amplification and multidrug resistance induced by the phosphatase-inhibitory tumor promoter, okadaic acid

The mechanism by which tumor promoters contribute to cellular transformation and tumorigenesis is not completely understood. To investigate further the molecular events involved in these processes, we used okadaic acid, a non-phorbol ester type tumor promoter that specifically inhibits certain protein phosphatases. We describe here that the continuous treatment of murine NIH 3T3 fibroblast cell cultures with okadaci acid resulted in a 50-fold amplification of two genes, mdr-1a and mdr-1b, that conferred multidrug resistance. As a consequence, the cells became cross-resistant to the cytotoxic effects of adriamycin, an antineoplastic drug used in the treatment of human tumors. Since genetic changes have been correlated with cell transformation and tumorigenesis, our results suggest that these processes may constitute an additional factor contributing to tumor promotion by okadaic acid.

Incorporation of 5-fluorouracil into U2 and U6 snRNA inhibits mRNA precursor splicing

The splicing activities of 5-fluorouracil (FUra)-substituted U2 and U6 small nuclear RNAs (snRNAs) were examined in an in vitro splicing system. Yeast splicing extracts were specifically depleted of endogenous U2 and U6 snRNAs by antisense oligonucleotide-directed RNase H hydrolysis. Splicing activity was recovered when the extracts were reconstituted with synthetic U2 and U6 snRNAs. However, U2 snRNA with all uracils substituted with FUra (FU2) did not restore any splicing activity. Nondenaturing gel electrophoresis showed that FU2 failed to promote the assembly of spliceosome complexes. The ability of U2 snRNA to restore splicing in U2-depleted extracts increased as FUra content decreased but was still only 60% of control activity at 25% substitution of uracils with FUra. Addition of FU2 to nondepleted extracts caused strong inhibition of splicing accompanied by increased degradation of the pre-mRNA, suggesting that FU2 forms an inactive complex with a protein splicing factor that normally binds to the pre-mRNA. FU6 restored full splicing activity to U6-depleted extracts, but at a 5-fold higher concentration than U6 snRNA. These results demonstrate that the incorporation of FUra can impair the functions of catalytic RNA molecules.

Quantitative determination of the ratio of mutated to normal ras genes in the blood of leukemia patients by allele-specific PCR

By combining allele-specific PCR amplification and a PCR-based quantitation approach, a method has been developed to estimate the mutated K-ras gene content in the blood of AML patients as a percentage of total K-ras. One PCR primer set was designed not to discriminate between mutant K-ras and wild-type K-ras and thus amplified the total K-ras gene. The other PCR primer set was designed to be allele-specific for K-ras gene containing a G to C mutation at codon 12. This primer set could discriminate the mutant and wild-type genes when the proportion of the mutated sequence was 0.2% of the total K-ras gene. To test the method on biological specimens, genomic DNA samples were analyzed from the peripheral blood of a patient who had secondary AML with the same codon 12 K-ras mutation. Two samples taken from this patient 2 months apart during follow-up had myeloblast cell contents of 67 and 80%. However, the percentage of mutated K-ras was 50% in both samples, suggesting that this patient may be inherently heterozygotic in this particular mutation. This ratio of mutated to normal K-ras in the patient's cells was confirmed by RNA-SSCP analysis and RNA sequencing. This quantitation method can provide a sensitive and specific estimation of the content of mutated K-ras alleles in patient samples.

Effect of 5-fluoro- and 5-bromouracil substitution on the translation of human thymidylate synthase mRNA

The synthesis of thymidylate synthase (TS) from 5-fluorouracil (FUra)- and 5-bromouracil (BrUra)-substituted mRNAs was examined to investigate the effect of incorporation of uracil (Ura) analogs on translation. Human TS cDNA was transcribed in the presence of Ura-, FUra-, or BrUTP to obtain 100% substituted mRNA. The mRNAs were translated in a rabbit reticulocyte lysate system. The TS protein that was formed from each of the templates reacted identically with TS antibody in Western blots. Time courses of TS formation revealed a characteristic peak which occurred at 45 min for the Ura- and FUra-RNAs and at 2 h for the BrUra-RNA. Substitution of Ura with FUra did not alter the rate of translation, while substitution of BrU for Ura decreased the rate of translation. Substitution of Ura with FUra or BrUra enhanced the stability of the mRNAs in the rabbit reticulocyte lysate by 3- and 10-fold, respectively. Incorporation of BrUra influenced the binding and catalysis on the ribosome, resulting in a 3.5-fold greater rate of activation (Kact) and 6-fold lower Vmax than the equivalent values for the Ura- and FUra-substituted mRNAs. Nondenaturing gel electrophoresis revealed that different conformations exist among the mRNAs. These data show that translation can be influenced by the incorporation of fraudulent bases into mRNA and those bases that stabilize RNA secondary structure will have the greatest inhibitory effect on translation.

Detection of clonal T-cell populations in gastrointestinal lymphomas by analysis of cRNA conformational polymorphisms of rearranged T-cell-receptor-gamma genes

Analysis of complementary RNA molecules of junctional regions of rearranged T-cell-receptor-gamma genes show a pattern of conformational polymorphisms which is specific for an individual lymphocytic clone. In a blinded study we analysed formalin-fixed, paraffin-embedded histological specimens from gastrointestinal lymphomas and control tissues (lymphomas: pleomorphic T-cell 10, anaplastic large cell [Ki1+] 9, centroblastic 5, immunocytoma 1, B-CLL 2, Hodgkin's 2, centroblastic-centrocytic 1, MALT [mucosa associated lymphoid tissue] 1, T-cell acute lymphoblastic leukaemia 1, non-lymphoid or polyclonal lymphoid tissues 5). Junctional regions of rearranged TCR-gamma genes were amplified by the polymerase chain reaction and the products were transcribed into cRNA. Conformational patterns of cRNA molecules were analysed by polyacrylamide gel electrophoresis. 13/20 T-lineage lymphomas and the T-cell acute lymphocytic leukaemia displayed a distinct cRNA band pattern, all B-lineage lymphomas and the non-lymphoid control tissues were negative. Only one case of nasopharyngeal (lymphoepithelial, Schmincke-Regaud) carcinoma showed a faint cRNA banding pattern. This novel and non-radioactive assay allows for the rapid detection and molecular characterization of clonal lymphoid populations in minute histological biopsy specimens.

Regulation of canine gallbladder motility by brain peptides

BACKGROUND

Brain peptides alter most gastrointestinal functions, but their effects on gallbladder motility have not been examined in detail.

METHODS

Studies were conducted in awake, male beagle dogs.

RESULTS

Of 30 brain peptides evaluated, thyrotropin-releasing hormone (TRH) and calcitonin gene-related peptide (CGRP) inhibited CCK- and meal-induced gallbladder contraction. These responses were abolished by ganglionic blockade. Truncal vagotomy prevented the central inhibitory action of TRH but not that of CGRP, whereas noradrenergic blockade prevented the central inhibitory action of CGRP but not that of TRH. Muscarinic blockade did not prevent the relaxing effect of cerebral TRH but pretreatment with the vasoactive intestinal peptide (VIP) antagonist, (4Cl-D-Phe6-Leu17)VIP, significantly attenuated gallbladder relaxation induced by cerebral TRH: the combination of both VIP and muscarinic antagonists abolished TRH-induced gallbladder relaxation. alpha-Adrenergic receptor blockade but neither beta-adrenergic blockade nor adrenalectomy abolished gallbladder relaxation induced by cerebral CGRP. Intravenous infusion of VIP and norepinephrine inhibited CCK-induced gallbladder contraction and these responses were abolished dose dependently by intravenous infusion of (4Cl-D-Phe6-Leu17)VIP and phentolamine, respectively.

CONCLUSIONS

Cerebral TRH inhibits canine gallbladder contraction by stimulation of vagal outflow and subsequent release of VIP acting via its specific receptor whereas cerebral CGRP inhibits gallbladder contraction by stimulation of sympathetic, noradrenergic outflow via alpha-adrenergic receptors.

Regulation of exocrine pancreatic secretion by cerebral TRH and CGRP: role of VIP, muscarinic, and adrenergic pathways

The central nervous system effects of thyrotropin-releasing hormone (TRH) and calcitonin gene-related peptide (CGRP) on exocrine pancreatic secretion were studied in freely moving rats. TRH (0.05-0.5 nmol) significantly stimulated, whereas CGRP (0.1-1.0 nmol) significantly inhibited, volume, protein, and bicarbonate secretion. Pretreatment of the animals with the ganglionic blocking agent chlorisondamine abolished the pancreatic responses produced by both peptides. In contrast, vagotomy abolished the stimulatory effect of TRH, whereas noradrenergic blockade with bretylium or phentolamine abolished the inhibitory effect of CGRP. Atropine significantly attenuated, but the vasoactive intestinal peptide (VIP) antagonist [D-p-Cl-Phe6, Leu17]VIP completely abolished the stimulatory effect of TRH. Pancreatic secretory responses stimulated by cerebral TRH or by peripheral VIP were inhibited dose dependently by peripheral [D-p-Cl-Phe6,Leu17]VIP. Inhibition of pancreatic secretion induced by cerebral CGRP or by peripheral norepinephrine was prevented by intravenous phentolamine. These results indicate 1) cerebral TRH stimulates and cerebral CGRP inhibits exocrine pancreatic secretion in freely moving rats; 2) the effects of TRH are mediated by vagal efferents, and the primary peripheral transmitter appears to be VIP acting on VIP receptors, whereas muscarinic efferents are less important; and 3) the effects of CGRP are mediated by sympathetic noradrenergic efferents via alpha-adrenergic receptors.