Glucocorticoid-induced cytolysis of human lymphoblastoid cells
Waddell, Andrew Waddell
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Glucocorticoids cause the regression of certain human leukaemias. As an in vitro model for this effect, I studied the action of methylprednisolone on human lymphoblastold cells. The cell line mainly used was BLA1, which was derived from a patient with acute lymphoblastic leukaemia. At 500ng/ml, methylprednisolone causes lysis of BLA1 cells after 48h exposure. The role of cytoplasmic glucocorticoid receptors in this cytolysis was investigated, and it was found that methylprednisolone-induced cytolysis is independent of receptor concentrations. Methylprednisolone causes reduction in the uptake of L-pathway amino acids and/facilitated diffusion of uridine and thymidine, while stimulating A-pathway uptake of amino acids, deoxyglucose and simple diffusion of uridine and thymidine. Again, there is no evidence to implicate glucocorticoid receptors in these processes. The mean volume of BLA1 cell populations is reduced on exposure to me thylprednisolone, and this appears to be the result of shrinkage of the cells and the appearance of small subcellular fragments. Alterations in the shape of cells are also found. There is an increase in the number of cells showing "blebs" on their surface which is maximal 2h after treatment. There is a later increase in the number of enlarged dead cells in the population. HeLa cells show similar changes, though somewhat more slowly. Lysis by methylprednisolone appears to be a widespread phenomenon in actively growing cell cultures. Attempts to grow cells resistant to 500pg/ml methylprednisolone were unsuccessful, although human red blood cells have increased stability in vitro at this concentration. The results of this work indicate that after treatment morphological changes typical of at least some stages of apoptosis and coagulative necrosis may be detected. It would appear that the effects that have been observed are mediated by changes induced in the surface of the cells, and there is no evidence that the "steroid-receptor-gene activation" model of hormone action applies. The relationship between the effects described and cell death by apoptosis is discussed.