Absence of<i>KLF6</i>gene mutation in 71 hepatocellular carcinomas
Authors: Sandrine Boyault, Aurélie Hérault, Charles Balabaud, Jessica Zucman‐Rossi
Journal: Hepatology (2005)

To the Editor: KLF6 is a gene encoding the Kruppel-like factor 6, a transcription factor involved in the regulation of cell proliferation and differentiation. Mutations of KLF6 have been reported in prostate cancer,1, 2 in astrocytic gliomas3 and in colon cancer.4 In a recent study, Kremer-Tal et al.5 reported somatic mutations of KLF6 in 6 of 41 hepatocellular carcinomas (HCCs). We have screened for KLF6 mutations in a larger series of HCCs to search for genotype-phenotype correlations. A series of 71 HCCs was collected after surgical resection in France. The sex ratio (M/F) was 4:1 and the mean age of the patients was 61 years. Risk factors for HCC of hepatitis B virus, hepatitis C virus, alcohol abuse and heamochromatosis occurred in 25%, 17%, 31%, and 4% of the tumors, respectively. All DNAs were extracted from frozen tissue sections after a pathological control. Direct sequencing of exon 2 of KLF6 was performed because almost all mutations previously found in tumors, including HCC, were clustered in this exon. Sequences were systematically determined on both DNA strands using a Big Dye terminator chemistry kit (Applied Biosystems, Foster City, CA). The sensitivity of our screening method has been previously validated in the same series of tumor DNA samples by the identification of β-catenin, TP53, and axin1 gene mutations in 34%, 21%, and 6% of the cases, respectively.6 In our series, we observed neither somatic nor germline mutations in KLF6. Known silent nucleotide polymorphisms were observed in two cases (R201R and S277S). The lack of KLF6 mutation observed in the 71 HCCs analyzed was significatively discordant with the 15% of mutations reported by analyzing 41 samples, Fisher exact test P = .001.5 This discrepancy is not likely to be due to a failure in our screening process since we found the usual frequency of β-catenin, TP53, and axin1 mutation in the same series of DNA when compared with similar published HCC series.7 A similar discrepancy in the frequency of KLF6 mutation has also been observed in prostate cancer and astrocytic gliomas: the high frequencies of KLF6 mutations initially reported in 55% of prostate cancer1 and in 9% of astrocytic gliomas3 have not been confirmed in 5 subsequent studies which found 0%-7% of mutations in prostate cancers2, 8, 9 and no mutation in astrocytomas and glioblastomas.10-12 The reasons for these discrepancies in KLF6 mutational frequency remain to be elucidated. One possible reason for the differences could be that the original study was carried out using DNA extracted from paraffin-embedded tissue samples, a procedure that has been previously shown to carry a risk of detecting false-positive nucleotide mutations.13 It is also possible that the differences may be due to differences in tumor sampling, including the geographical origin of patients, variation in risk factors and/or in tumor grade since these information were not provided by Kremer-Tal et al.5 Finally, the absence of KLF6 mutation in our study suggests at best a minor role for mutations in this gene in hepatocarcinogenesis. Sandrine Boyault*, Aurélie Hérault*, Charles Balabaud , Jessica Zucman-Rossi*, * Inserm U434, Paris, France, Inserm E362, Bordeaux, France.