Dear Editor,

I have read with much interest the recent paper published in Cell Death and Disease by Lanzino et al.1 In that paper, the authors propose the existence of a regulatory mechanism used by androgens to repress aromatase expression in breast cancer cells that involves the orphan nuclear receptor DAX-1. I would like to attract the readers’ attention on the fact that in that paper all experiments involving visualization of DAX-1 were obtained using the commercial K-17 antibody from Santa Cruz Biotechnology. I believe that extreme caution should be taken to evaluate results generated by the use of that antibody. Helguero et al.2 compared the performance of several antibodies directed against DAX-1 in immunoblot and immunofluorescence. They found that the K-17 anti-DAX-1 antibody recognizes with high affinity a 65-kDa band (DAX-1 molecular weight is 52 kDa) in HeLa whole-cell extracts. This cell line expresses only extremely low levels of DAX-1 mRNA. Moreover, immunofluorescence experiments using the K-17 anti-DAX-1 antibody showed a homogeneous nuclear signal in cell types (HeLa and T47-D) that resulted negative when stained with other anti-DAX-1 antibodies (2ZH7, A0179 and 2F4) that recognized specifically a band of molecular weight around 50 kDa in immunoblot. Those results are entirely consistent with our own data showing that in HeLa cells transfected with a DAX-1 expression vector and costained with the rabbit K-17 and the mouse 2F43 anti-DAX-1 antibodies, only a few cells, as expected, are stained with the 2F4 antibody with a prevalently nuclear pattern, whereas all cells are homogeneously stained by the K-17 antibody in the nucleus (Supplementary Figure 1). Taken together with the results previously published by Helguero et al.,2 these data show that the K-17 antibody nonspecifically recognizes a nucler antigen expressed at high levels in HeLa cells and in all other cell lines analyzed (our unpublished observations). Several other studies in addition to Lanzino et al.1 have also used the K-17 antibody to assess DAX-1 expression, both in immunoblot and in immunofluorescence/immunohistochemistry (see Lalli and Alonso4 for a review), without checking its specificity. The purpose of this correspondence is then to alert scientists working in the DAX-1 field about the pitfalls linked to the use of the K-17 antibody to detect DAX-1 in cell lines and tissues and to encourage the use of more specific antibodies against DAX-1.