Methylation patterns in human androgen receptor gene and clonality analysis

Tumor clonality, an important issue in tumor biology, has been analyzed using X-chromosome inactivation studies based on the differential methylation patterns of active and inactive alleles. Recently, a PCR-based androgen receptor gene (AR) analysis method was developed that takes advantage of highly polymorphic CAG repeats and nearby HpaII and HhaI sites in exon 1 of AR at the Xq13 region. However, the data from this assay, which is now widely used, are sometimes uninterpretable and irreproducible for some currently unclear reason. To determine that reason, we analyzed a panel of lung cancer cell lines, using HpaII or HhaI restriction enzymes, methylation-specific PCR, and bisulfite genomic sequencing of the polymorphic CAG repeat site of AR exon 1, including nearby CpG sites. We found direct evidence of a variable methylation pattern at the restriction sites that prevented proper enzyme cleavage in two lung cancer cell lines (NCI-H292 and NCI-H1944) obtained from female patients who had a polymorphic CAG repeat in AR exon 1. Our data suggest that methylation patterns at the CpG sites of AR exon 1 are complicated and vary among different individuals. Therefore, the reliability of the PCR-based clonality analysis may require further evaluation.