The BCL10 gene was isolated from the breakpoint region of the t(1;14) in mucosa-associated lymphoid tissue (MALT) lymphomas,1,2 and BCL10 was found to be a cellular homologue of the equine herpesvirus-2 E10 gene because both contain an amino-terminal caspase recruitment domain, which is homologous to that seen in several apoptotic molecules.1,2 In functional assays, wild-type BCL10 was found to induce apoptosis. It is noteworthy that BCL10 in t(1;14)-bearing MALT lymphomas exhibits a variety of truncating mutations,1,2 and that truncated BCL10 fails to induce apoptosis and exhibits a transforming activity. Similar mutations were also identified in a subset of follicular lymphoma (FCL) and other tumor cell lines with a loss of heterozygosity in chromosome 1p22.1 However, several recent studies, including ours, have reported that BCL10 mutations are rare in various human tumors, thus raising questions regarding the pathological role of BCL10 as a tumor suppressor gene in these tumors.3-9 

Recently, Dyer et al suggested that at least some of the discrepancies between their data and those reported by others can be ascribed to their use of cDNA rather than genomic DNA.10 They found that nucleotide insertions and deletions within homopolymeric runs of 8 adenines and 7 thymidines are common in BCL10 cDNAs. In order to investigate whether BCL10 abnormalities occur at the RNA level, we searched for somatic mutations in BCL10 cDNAs by means of reverse transcription polymerase chain reaction (RT-PCR) and sequencing analyses in 3 normal peripheral blood leukocytes (PBLs) and 3 FCL samples. The pathological diagnosis was established in accordance with the revised European-American classification of lymphoid neoplasms (REAL). The coding region of BCL10 cDNAs (702 bp) was amplified by using Taq DNA polymerase with high fidelity and subcloned into the plasmid vectors. The inserts of 5 independent BCL10 cDNA clones from each of the normal PBLs or lymphoma samples were sequenced in both directions using an ABI PRISM Dye Terminator Cycle Sequencing Ready Reaction Kit (Perkin Elmer, Foster City, CA) on an ABI 373 DNA automated sequencer (Applied Biosystems, Foster City, CA). The spectrum of BCL10 cDNA abnormalities is summarized in the Table. These include multiple point mutations and nucleotide insertions or deletions within homopolymeric runs of adenines and thymidines. The spectrum of multipleBCL10 cDNA abnormalities is similar to those reported by others in certain tumors.1,2,10 It is possible that some of these multiple point mutations may be due to PCR or cloning artifacts. In our study, however, nucleotide insertions or deletions within homopolymeric runs, resulting in truncation of BCL10, were identified in the same 8 out of 15 clones both from normal PBLs and from FCL samples (Table). The possibility that these truncation-type abnormalities are due to PCR or cloning artifacts is minute, because only 4 out of 500 genomic DNA sequences were found to exhibit such insertions or deletions10 and our FCL samples exhibited an apparently normal germ-line DNA.9 Finally, a novel 118 bp deletion in exon 3 of BCL10 was identified in one FCL sample. It is not clear if this alteration contributes to the pathogenesis of FCL, but in the light of the fact that only one clone carried such a deletion, it is doubtful whether this deletion has any functional significance.

In summary, our results strongly suggest that BCL10 may undergo a novel posttranscriptional RNA modification even in normal PBL cells and that BCL10 cDNA abnormalities are not necessarily associated with the molecular pathogenesis of a wide range of human tumors.

Summary of BCL10 cDNA sequence abnormalities in 3PBL and 3FCL

  Clone No.  Alteration  Coding Exon  Codon Mutation Type  Size (Full Length = 233aa) 
Normal  1  1  400T → C  3  134  Ser → Pro 233aa  
 PBL   2  nil     233aa 
  3  136delA  2  46  Truncation   68aa 
  4  114T → C  2  38  Silent 
   501T → C  3  167  Silent  233aa 
   655A → G  3  219  Ser → Gly 
  5  152A → G  2  51  Asp → Gly  233aa 
 2  1  39C → T  1  13  Silent  233aa 
  2  64G → T  2  22  Truncation   21aa 
  3  272insA  2  91  Truncation  101aa 
  4  137insA  2  46  Truncation   48aa 
  5  33G → T  1  11  Glu → Asp  233aa 
 3  1  137insA  2  46  Truncation   48aa 
  2  89A → G  2  30  Glu → Gly 
   136delA  2  46  Truncation  68aa 
  3  386C → T  3  129  Silent 
   453T → C  3  151  Silent  233aa 
   638G → A  3  213  Gly → Glu 
  4  136delA  2  46  Truncation   68aa 
  5  24G → C  1  8  Silent  68aa 
   136delA  2  46  Truncation  
FCL  1  272insA  2  91  Truncation  101aa  
  157G → A  2  53  Glu → Lys  233aa  
  195T → A  2  65  Silent  233aa  
  321A → G  2  107  Silent  168aa  
   500insT  3  167  Truncation 
  5  500insT  3  167  Truncation  168aa 
 2  1  521T → A  3  174  Truncation  173aa 
  2  136delA  2  46  Truncation   68aa 
  3  nil     233aa  
  4  137insA 2  46  Truncation   48aa  
  5  nil    233aa  
 3  1  nil     233aa 
  2  135A → G  2  45  Silent 
   317T → C  2  106  Leu → Pro  178aa 
   504del118  3  168-208  Deletion 
  3  500insT  3  167  Truncation  168aa 
  4  470A → G  3  157  Glu → Gly 
   476A → G  3  159  Glu → Gly  168aa 
   500insT  3  167  Truncation  
  nil     233aa 
  Clone No.  Alteration  Coding Exon  Codon Mutation Type  Size (Full Length = 233aa) 
Normal  1  1  400T → C  3  134  Ser → Pro 233aa  
 PBL   2  nil     233aa 
  3  136delA  2  46  Truncation   68aa 
  4  114T → C  2  38  Silent 
   501T → C  3  167  Silent  233aa 
   655A → G  3  219  Ser → Gly 
  5  152A → G  2  51  Asp → Gly  233aa 
 2  1  39C → T  1  13  Silent  233aa 
  2  64G → T  2  22  Truncation   21aa 
  3  272insA  2  91  Truncation  101aa 
  4  137insA  2  46  Truncation   48aa 
  5  33G → T  1  11  Glu → Asp  233aa 
 3  1  137insA  2  46  Truncation   48aa 
  2  89A → G  2  30  Glu → Gly 
   136delA  2  46  Truncation  68aa 
  3  386C → T  3  129  Silent 
   453T → C  3  151  Silent  233aa 
   638G → A  3  213  Gly → Glu 
  4  136delA  2  46  Truncation   68aa 
  5  24G → C  1  8  Silent  68aa 
   136delA  2  46  Truncation  
FCL  1  272insA  2  91  Truncation  101aa  
  157G → A  2  53  Glu → Lys  233aa  
  195T → A  2  65  Silent  233aa  
  321A → G  2  107  Silent  168aa  
   500insT  3  167  Truncation 
  5  500insT  3  167  Truncation  168aa 
 2  1  521T → A  3  174  Truncation  173aa 
  2  136delA  2  46  Truncation   68aa 
  3  nil     233aa  
  4  137insA 2  46  Truncation   48aa  
  5  nil    233aa  
 3  1  nil     233aa 
  2  135A → G  2  45  Silent 
   317T → C  2  106  Leu → Pro  178aa 
   504del118  3  168-208  Deletion 
  3  500insT  3  167  Truncation  168aa 
  4  470A → G  3  157  Glu → Gly 
   476A → G  3  159  Glu → Gly  168aa 
   500insT  3  167  Truncation  
  nil     233aa 

Abbreviations: PBL, peripheral blood leukocytes; FCL, follicular lymphoma; aa, amino acid.

References

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