Levels of 70-kDa heat shock protein through the cell cycle in several mammalian cell lines

Seven different cell lines were analyzed by flow cytometry to evaluate the variation in heat shock protein hsp70 through the cell cycle. Inducible (hsp72) or both constitutive and inducible (hsp70) heat shock proteins were measured with monoclonal antibodies, and the cell cycle distribution was simultaneously measured with propidium iodide. Cell lines analyzed were Rat-1, Hr-24 (Rat-1 transfected with human hsp 72 gene), CHO (Chinese hamster ovary), C3H-10T1/2, AG1522 (normal human foreskin), GM2149 (normal human female skin), and Hela. None of the cell lines had a substantial variation in hsp72 or hsp70 levels through the cell cycle if they were not heated. In contrast, after chronic heating at 42.0 degrees C for 7.5 h, different cell lines had different patterns of hsp72 or hsp70 through the cell cycle. These results demonstrate that the level of hsp70 is not regulated differentially through the cell cycle in a variety of mammalian cell lines under normal unheated conditions. However, heat shock does induce cell-cycle-specific regulation of hsp70, which varies for different cell lines.