Methylation changes in promoter and enhancer regions of the WT1 gene in Wilms' tumours.

Although the WT1 gene has been implicated in the aetiology of Wilms' tumour, mutations in WT1 are found only in minority of the tumours. DNA methylation of regulatory elements represents another possibility of modulation of gene expression. We studied methylation in the promoter and enhancer regions of the WT1 gene in 34 Wilms' tumour patients by the polymerase chain reaction on HpaII-digested DNA and by the bisulphite method. No methylation was detected in the promoter region in either tumour or normal kidney or blood DNA samples. In contrast, a HpaII site in the enhancer region was at least partially methylated in normal kidney and blood DNA samples and in about one-third of the tumours, while the majority of tumours showed no methylation. The differential methylation in the enhancer region of the WT1 gene may indicate that methylation of this element can play a role in the regulation of this gene.

Role of tyrosine kinase signaling for beta-cell replication and survival.

Diabetes mellitus is commonly considered as a disease of a scant beta-cell mass that fails to respond adequately to the functional demand. Tyrosine kinases may play a role for beta-cell replication, differentiation (neoformation) and survival. Transfection of beta-cells with DNA constructs coding for tyrosine kinase receptors yields a ligand-dependent increase of DNA synthesis in beta-cells. A PCR-based technique was adopted to assess the repertoire of tyrosine kinases expressed in fetal islet-like structures, adult islets or RINm5F cells. Several tyrosine kinase receptors, such as the VEGFR-2 (vascular endothelial growth factor receptor 2) and c-Kit, were found to be present in pancreatic duct cells. Because ducts are thought to harbor beta-cell precursor cells, these receptors may play a role for the neoformation of beta-cells. The Src-like tyrosine kinase mouse Gtk (previously named Bsk/Iyk) is expressed in islet cells, and was found to inhibit cell proliferation. Furthermore, it conferred decreased viability in response to cytokine exposure. Shb is a Src homology 2 domain adaptor protein which participates in tyrosine kinase signaling. Transgenic mice overexpressing Shb in beta-cells exhibit an increase in the neonatal beta-cell mass, an improved glucose homeostasis, but also decreased survival in response to cytokines and streptozotocin. It is concluded that tyrosine kinase signaling may generate multiple responses in beta-cells, involving proliferation, survival and differentiation.

Two Li-Fraumeni syndrome families with novel germline p53 mutations: loss of the wild-type p53 allele in only 50% of tumours.

We describe two Li-Fraumeni syndrome families. Family A was remarkable for two early childhood cases of adrenocortical tumours, family B for a high incidence of many characteristic cancers, including a childhood case of choroid plexus tumour. Using direct sequencing, we analysed exons 5-9 of the p53 gene in constitutional DNA of individuals from both families and found two novel germline mutations in exon 5. In family A, we detected a point substitution in codon 138 (GCC to CCC), which resulted in the replacement of the alanine by a proline residue. Family B harboured a single-base pair deletion in codon 178 (CAC to -AC), resulting in a frameshift and premature chain termination. Three out of six tumours examined from both families, a renal cell carcinoma, a rhabdomyosarcoma and a breast cancer, showed loss of heterozygosity and contained only the mutant p53 allele. The remaining three neoplasms, both adrenocortical tumours and the choroid plexus tumour retained heterozygosity. Immunohistochemistry with anti-p53 antibody confirmed accumulation of p53 protein in tumours with loss of heterozygosity, while the remaining tumours were p53 negative. These results support the view that complete loss of activity of the wild-type p53 need not be the initial event in the formation of all tumours in Li-Fraumeni individuals.

[A method for detection of germinal mutations in the p53 tumor suppressor gene]. / Metodika detekce zárodecných mutací v tumor supresorovém genu p53.

BACKGROUND: The tumour suppressor gene p53 is exhibits somatic mutations in a high proportion of human tumours. In addition, there are cancer families suffering from the Li-Fraumeni syndrome, the members of which carry germ line mutations in this gene. The carriers of the p53 germ line mutations have a high risk of developing tumours. The genetic diagnosis of carriership of the mutation in the tumour family members is important for preventive measures and for eventual tumour therapy modification. METHODS AND RESULTS: We have developed a method for the detection of germ line mutations in the p53 gene based on non-radioactive SSCP and direct sequencing of PCR products. We have proved the efficiency of the method by finding known mutations in eight tumour cell lines. In our collection of tumour families we have detected polymorphisms in exons 4 and 6 of the p53 gene. In one family which conformed to the criteria of the Li-Fraumem syndrome we have found a novel germ line mutation in exon 5. CONCLUSIONS: The method developed by us is very simple and sensitive. The germ line mutations in the p53 gene are very rare.

Plasma somatostatin and plasma glucagon in long-term IDDM without residual B-cell function. No effect of different long-term metabolic control.

To further study the elevated plasma somatostatin (SRIF)--and reduced plasma glucagon concentrations found in IDDM patients without residual B-cell function compared to normal controls, we investigated 39 such patients, randomly assigned to three different insulin treatment regimens; conventional therapy with two injections a day (CTh), insulin pump (CSII) and multiple injections (MI), for 1 year. They were given an arginine infusion (0.5 g/kg/20 min). The mean basal plasma SRIF values in the CTh, CSII and MI groups were 20.8 +/- 3.3, 18.6 +/- 1.8 and 20.6 +/- 2.8 pmol/l and the mean basal plasma glucagon values were 30 +/- 5.7, 19 +/- 2.3 and 27 +/- 4.7 pmol/l, respectively. Both SRIF and glucagon increased in all groups in relation to arginine infusion. For both hormones, the mean values were highest in the CTh group, lowest in the CSII group, although the differences were not significant. The mean HbA1 values for the last 3 months within the test were 10.0 +/- 0.5, 8.8 +/- 0.3 and 9.1 +/- 0.5%, respectively, in the same order as above. The CTh group had significantly higher HbA1 values than the CSII group (p less than 0.02). We conclude that small differences in long-term blood glucose control are of inconsiderable importance for the islet hormonal response to arginine found in IDDM without B-cell function.

Somatostatin, insulin and glucagon after arginine stimulation in active and treated acromegaly.

Ten acromegalic patients, 28-71 years old, were compared with 10 normal controls, 21-39 years old. In another study, 7 patients with active acromegaly, 19-70 years old, were investigated before and 4-9 months following transsphenoidal adenectomy and radiation. They were all investigated following an arginine infusion (0.5 g/kg/20 min). Although the mean plasma somatostatin (somatotrophin release inhibiting factor (SRIF] was somewhat higher in acromegalic patients compared to normal controls (mean basal values 21 +/- 3.8 and 16.6 +/- 2.1 pmol/l, respectively), the difference was not significant. The patients had higher serum insulin (peak values 118 +/- 23.9 and 63 +/- 11.8 mU/l, respectively) and lower plasma glucagon (peak values 171 +/- 29.0 and 310 +/- 52.7 pmol/l, respectively). Plasma SRIF increased during arginine infusion, but the concentrations were similar before and following the operation (mean basal values 18.2 +/- 2.6 and 15.2 +/- 2.3 pmol/l, respectively). Serum insulin was significantly higher before the operation (peak values 154 +/- 38.8 and 91 +/- 24.9 mU/l, respectively). Plasma glucagon was similar before and after the operation (peak values 143 +/- 23.4 and 127 +/- 22.7 pmol/l, respectively). Plasma SRIF is similar in active acromegaly and normal controls, and in acromegaly before and following treatment, despite differences in serum growth hormone (GH), serum insulin and plasma glucagon. This points towards a modulating role for GH on plasma SRIF, possibly by affecting the other islet cell hormones.

Arginine infusion increases peripheral plasma somatostatin in man.

A somatostatin (SRIF) radioimmunoassay is described, using an antiserum raised in rabbit, reacting more with SRIF-14 than -28. Glass tubes were employed for the assay because our tracer, 125I 1-Tyr-SRIF, was adsorbed to plastic (23% non specific binding). Vycor extraction was used, and following Sephadex G-50 chromatography, the plasma extract showed two forms, coeluting with SRIF-28 and -14. Fifteen healthy subjects, eight women and seven men, 21-39 years old, received an infusion of arginine chloride (2.38 mmol/kg) for 20 min, or saline. An immediate rise in plasma SRIF from the mean basal level at 2 min was shown. Maximal value was 24.0 +/- 3.0 pmol/l (P less than 0.01) after 10 min followed by a rapid descent towards the basal level after the infusion. A temporal relationship was observed between the SRIF, insulin and glucagon responses following arginine infusion, while the GH levels increased only after the SRIF levels had declined, indicating an inhibition of GH. This is further supported by the high degree of correlation (r = 0.87) between SRIF- and GH increments. It is suggested that plasma SRIF measurement during arginine infusion gives an estimate of the pancreatic SRIF releasing capacity.