High expression of Mcl-1 in ALK positive and negative anaplastic large cell lymphoma

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Abstract
Aim: To gain more insight into the genes involved in the aetiology and pathogenesis of anaplastic large cell lymphoma (ALCL). Methods: Serial analysis of gene expression (SAGE) was undertaken on the CD4+ALK+ (anaplastic lymphoma kinase positive) ALCL derived cell line Karpas299 and as comparison on CD4+ T cells. Quantitative reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry were performed on five ALCL derived cell lines and 32 tissue samples to confirm the SAGE data. Results: High expression of Mcl-1 was seen in the Karpas299 cell line, whereas the two other antiapoptotic Bcl-2 family members, Bcl-2 and Bcl-XL, were not detected in the SAGE library. Quantitative RT-PCR confirmed the high expression of Mcl-1 mRNA and low expression of Bcl-2 and Bcl-XL in Karpas299 and in four other ALCL cell lines. To expand on these initial observations, primary tissue samples were analysed for Mcl-1, Bcl-XL, and Bcl-2 by immunohistochemistry. All 23 ALK+ and nine ALK− ALCL cases were positive for Mcl-1. Bcl-2 and Bcl-XL were expressed infrequently in ALK+ ALCL cases, but were present in a higher proportion of ALK− ALCL cases. Conclusion: The consistent high expression of Mcl-1 in ALK+ and ALK− ALCL suggests that Mcl-1 is the main antiapoptotic protein in this disease. The high frequency of Mcl-1, Bcl-2, and Bcl-XL positive ALCL cases in the ALK− group compared with the ALK+ group indicates that ALK induced STAT3 activation is not the main regulatory pathway in ALCL.