Specific inactivation of lysosomal glycosidases in living fibroblasts by the corresponding glycosylmethyl-p-nitrophenyltriazenes.

Glicentin (a highly purified 100-amino acid peptide with glucagon-like immunoreactivity from porcine gut) was subjected to limited digestion with trypsin and carboxypeptidase B, and the resulting peptides were studied by gel filtration and region-specific glucagon radioimmunoassays. Similar digests of glucagon and purified fragments of glucagon were studied in parallel. Glicentin gave rise to peptides that corresponded closely to the 1-17 and 19-29 fragments of glucagon. Also, 125I-labelled glicentin and 125I-labelled glucagon gave rise to identical fragments after trypsin treatment. On the basis of this and other evidence [Jacobsen, Demandt, Moody & Sundby (1977) Biochim. Biophys. Acta 493, 452-459] it is concluded that glicentin contains the entire glucagon sequence at residues number 64-92 and thus fulfills one of the requirements for being a 'proglucagon'.     

Isocitrate dehydrogenase 1 R132C mutation occurs exclusively in microsatellite stable colorectal cancers with the CpG island methylator phenotype

The CpG Island Methylator Phenotype (CIMP) is fundamental to an important subset of colorectal cancer; however, its cause is unknown. CIMP is associated with microsatellite instability but is also found in BRAF mutant microsatellite stable cancers that are associated with poor prognosis. The isocitrate dehydrogenase 1 (IDH1) gene causes CIMP in glioma due to an activating mutation that produces the 2-hydroxyglutarate oncometabolite. We therefore examined IDH1 alteration as a potential cause of CIMP in colorectal cancer. The IDH1 mutational hotspot was screened in 86 CIMP-positive and 80 CIMP-negative cancers. The entire coding sequence was examined in 81 CIMP-positive colorectal cancers. Forty-seven cancers varying by CIMP-status and IDH1 mutation status were examined using Illumina 450K DNA methylation microarrays. The R132C IDH1 mutation was detected in 4/166 cancers. All IDH1 mutations were in CIMP cancers that were BRAF mutant and microsatellite stable (4/45, 8.9%). Unsupervised hierarchical cluster analysis identified an IDH1 mutation-like methylation signature in approximately half of the CIMP-positive cancers. IDH1 mutation appears to cause CIMP in a small proportion of BRAF mutant, microsatellite stable colorectal cancers. This study provides a precedent that a single gene mutation may cause CIMP in colorectal cancer, and that this will be associated with a specific epigenetic signature and clinicopathological features.