Chronic exposure to bryostatin-1 increases the radiosensitivity of U937 leukaemia cells ectopically expressing Bcl-2 through a non-apoptotic mechanism.
OBJECTIVE
Ionizing radiation (IR) produced a dose-dependent increase in apoptosis in U937/pCEP4 cells which was attenuated by the stable over expression of Bcl-2 (U937/Bcl-2). A dose of 2 Gy IR was selected for further analyses to determine if subsequent exposure to 10nM bryostatin- would overcome the resistance to IR-induced apoptosis conferred by Bcl-2 over expression.


RESULTS
Although bryostatin- did not increase IR-induced apoptosis in U937/pCEP4 or U937/Bcl-2 cells, it impaired mitochondrial function and increased the antiproliferative effects of IR in both cell lines. The effects were more pronounced in U937/Bcl-2 cells. Bryostatin-1 also exerted differential effects on cell-cycle distributions of U937 transfectant cells, producing a significant G0/G1 arrest in U937/Bcl-2 cells, while decreasing IR-induced G2/M arrest in U937/pCEP4 cells. Although Bcl-2 over expression attenuated IR-induced apoptosis, clonogenic survival was similar in U937/pCEP4 and U937/Bcl-2 cells following 2 Gy IR treatment. Treatment with 10nM bryostatin-1 after 2 Gy IR further reduced clonogenic survival in both cell lines. Moreover, U937/Bcl-2 cells were more susceptible to the growth-inhibitory effects of IR/bryostatin-1 than U937/pCEP4 cells.


CONCLUSIONS
Bryostatin-1 increased the radiosensitivity of U937 transfectant cell lines without enhancing apoptosis; furthermore, U937/Bcl-2 cells were more susceptible to IR/bryostatin-1-mediated antiproliferative effects than their empty-vector counterparts.
Cartee
L
L
Department of Medicine, Virginia Commonwealth University, Medical College of Virginia, Richmond 23298, USA.
Davis
C
C
Lin
P S
PS
Grant
S
S
D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D054713:Bryostatins; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D007783:Lactones / Q000627:therapeutic use*; D018942:Macrolides; D008928:Mitochondria / Q000187:drug effects / Q000528:radiation effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology*; D011838:Radiation-Sensitizing Agents / Q000627:therapeutic use*; D020298:U937 Cells
D054713:Bryostatins; D007783:Lactones; D018942:Macrolides; D019253:Proto-Oncogene Proteins c-bcl-2; D011838:Radiation-Sensitizing Agents; C046785:bryostatin 1