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. 2000 Aug;47(2):268–271. doi: 10.1136/gut.47.2.268

Alterations of the PPP2R1B gene located at 11q23 in human colorectal cancers

Y Takagi 1, M Futamura 1, K Yamaguchi 1, S Aoki 1, T Takahashi 1, S Saji 1
PMCID: PMC1727986  PMID: 10896920

Abstract

BACKGROUND/AIMS—In 1998 the PPP2R1B gene encoding the A subunit of the serine/threonine protein phosphatase was identified as a putative tumour suppressor gene in lung and colon cancer in the chromosome region 11q22-24. The aim of the present study was to determine the type of alterations in primary rectal cancers as well as colon cancers and the correlation between these alterations and clinicopathological data.
METHODS—Mutation analyses of the PPP2R1B gene sequence encoding the binding sites of the catalytic C subunit (Huntington elongation A subunit TOR (HEAT) repeats 11-15) and partial binding sites of the regulatory B subunit were carried out on cDNA samples from 30 primary colorectal cancer specimens and corresponding normal tissues using a combination of the polymerase chain reaction and subsequent direct DNA sequencing.
RESULTS—Five missense mutations producing amino acid substitutions were detected in the four colon cancer cases (13.3%; four of 30 colorectal cancers): 15glycine (GGT) to alanine (GCT) and 499leucine (TTA) to isoleucine (ATA) in the same case, and 498valine (GTG) to glutamic acid (GAG), 500valine (GTA) to glycine (GGA), and 365serine (TCT) to proline (CCT). Of these five mutations, three (60%) were located in HEAT repeat 13 and four (80%) showed T to other nucleotide substitutions. In addition, a normal polymorphism, 478leucine, was found. No correlation was found between these mutations and clinicopathological data.
CONCLUSION—Our results suggest that the PPP2R1B gene is one of the true targets at 11q23, and its inactivation is involved in the development of all types of colorectal cancers.


Keywords: PPP2R1B gene; colorectal cancer; tumour suppressor gene; protein phosphatase

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Figure 1  .

Figure 1  

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Schematic view of PPP2R1B cDNAs. Three sets of polymerase chain reaction primers were used to amplify a portion of the gene. Numbers indicate the internal repeats (HEAT repeats) and shaded numbers indicate the sequence of binding sites for the PP2Ac subunit on the PR65/A subunit.

Figure 2  .

Figure 2  

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DNA sequence electropherograms showing the PPP2R1B gene mutations identified in patients with colorectal cancer. Individual electropherograms for the tumour are shown in the upper panels and the corresponding normal tissues (controls) are shown in the lower panels. The relevant nucleotide is indicated by an arrow.

Figure 3  .

Figure 3  

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DNA sequence showing a single base substitution without amino acid substitution of the PPP2R1B gene. The consensus sequence is shown in the upper panel and an identified substitution is shown in the lower panel.

Figure 4  .

Figure 4  

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Multiple sequence alignment of HEAT motif sequences and location of the mutations and polymorphism. Boxed amino acids represent highly conserved residues and shaded amino acids indicate hydrophobic residues. Amino acids underlined are mutated except for L ( 478Leu ) in HEAT repeat 12. 

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