The transcription factor ATF5 is widely expressed in carcinomas, and interference with its function selectively kills neoplastic, but not nontransformed, breast cell lines.

ATF5, a transcription factor important in differentiation, proliferation and survival, has been found to be highly expressed in neural progenitor cells and in certain tumors including glioblastomas (GBMs), but its expression in other normal and neoplastic tissues has not been extensively investigated. A tissue microarray immunostained for ATF5 showed diffuse nuclear expression (as defined by the presence in greater than 25% of cells) in 63% (117/186) of neoplastic samples, when compared to only 32% (20/62) in nonneoplastic tissues. When analyzed by histologic subtype, a significantly greater proportion of adenocarcinomas, transitional cell carcinomas, squamous cell carcinomas and metastatic carcinomas of various tissue origins had nuclear staining when compared to nonneoplastic tissues. There was no significant difference in ATF5 expression in renal cell carcinomas, lymphomas and seminomas, when compared to nonneoplastic tissues. An expanded series of nonarray breast resection specimens revealed a significantly greater proportion of ATF5 positivity in ductal and lobular carcinomas, when compared to normal breast tissue. Past work found that loss of ATF5 function triggers death of GBM cells, but not of normal activated astrocytes. Here, we observed that loss of ATF5 function caused significant apoptotic death of neoplastic breast cell lines, but not of nonneoplastic breast cell lines. Our data demonstrate elevated ATF5 expression in a wide variety of neoplasms and that interference with ATF5 function selectively triggers death of breast carcinoma cells. Such findings may have potential therapeutic application.