Activating Transcription Factor 3 (ATF3) Is Overexpressed in Classical Hodgkin Lymphoma and Is Required for Survival of Hodgkin and Reed-Sternberg Cells in Response to Cellular Stress.

Hodgkin and Reed-Sternberg (HRS) cells display aberrant activity of several transcription factors, including nuclear factor kappa B (NF-kB) and members of the activator protein-1 (AP-1) family, that promote cytokine expression, cellular survival and proliferation. Using oligonucleotide microarrays, we set out to identify additional factors which are responsible for the malignant phenotype of HRS cells. Microarray analysis and subsequent Northern and Western blotting revealed that activating transcription factor 3 (ATF3), a member of the CREB/ATF family of transcription factors that is involved in the cellular response to stress signals, shows a strong constitutive expression in Hodgkin-derived cell lines. In contrast, ATF3 expression could not be detected in several Non-Hodgkin cell lines of distinct differentiation stages, ranging from pre-B cell lines to plasma B cell lines. To investigate the expression pattern of ATF3 in primary tumor cells, we performed immunohistochemistry on tissue microarrays. Immunohistochemistry confirmed a strong expression of ATF3 in primary HRS cells with a nuclear staining pattern. ATF3 expression was observed in almost all cases of classical Hodgkin lymphoma examined (69/71), whereas ATF3 expression was not detected in lymphocyte-predominant Hodgkin lymphoma. In addition, a significant number of anaplastic large cell lymphomas revealed a nuclear ATF3 staining pattern. In contrast, among all other B and T cell Non-Hodgkin lymphomas, ATF3 expression was observed only in rare cases (7/244), indicating that ATF3 expression is almost exclusively restricted to classical Hodgkin lymphoma and to a subset of anaplastic large cell lymphomas. To investigate the role of ATF3 for proliferation and survival of HRS cells, we generated vector-based siRNA constructs to downregulate ATF3 expression. Our vector system carries a puromycin-resistance gene thus allowing selection of siRNA expressing cells. Transfection of Hodgkin-derived cell lines with ATF3 siRNA constructs and subsequent selection of siRNA-expressing cells demonstrated a dramatic loss of viable cells. Our observations indicate that ATF3 is required for the survival of HRS cells exposed to the environmental stress imposed by antibiotic selection.