Regulation of the synthesis of bcl-2 protein by growth factors.
The sensitivity of AML blast stem cells can be measured in cell culture, using a clonogenic assay to determine survival after each of a graded series of drug concentrations. For cytosine arabinoside, the dose-response curve is a simple negative exponential that can be described by a D10 value, a measure of slope. This D10 value can be affected by regulatory molecules added to the cultures. All-trans retinoic acid (ATRA) usually sensitizes cells, while hydrocortisone (HC) is protective. Growth factor responsive cells are more Ara-C sensitive in G-CSF than in GM-CSF or IL-3. The proto-oncogene bcl-2 may be part of the mechanism by which drug sensitivity is regulated. Previous work has shown that ATRA decreases bcl-2 RNA expression and the half-life of the protein; in contrast, the protein from cells treated with HC is more stable than controls. Growth factors were not shown to change either expression of bcl-2 RNA or the stability of its protein. In this paper, we describe experiments where OCI/AML-1 cells were grown in G-CSF and then transferred to medium containing both G-CSF and the GM-CSF-IL-3 fusion protein pIXY. Steady-state levels of bcl-2 protein were measured by Western blot and synthesis by incorporation of 35S methionine into protein. We observed that both measures doubled within 12-24 h after transfer from G-CSF in G-CSF with pIXY, but promptly returned to the previous state when pIXY was withdrawn. We conclude that growth factors regulate that activity of bcl-2 post-transcriptionally by altering the rate of synthesis of the protein.
Hu
Z B
ZB
The Ontario Cancer Institute/Princess Margaret Hospital, Toronto, Canada.
Minden
M D
MD
McCulloch
E A
EA
D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D003561:Cytarabine / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D004354:Drug Screening Assays, Antitumor; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology*; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology*; D007951:Leukemia, Myeloid / Q000188:drug therapy / Q000378:metabolism*; D000090063:Proto-Oncogene Mas; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis*; D011993:Recombinant Fusion Proteins / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000187:drug effects
D000964:Antimetabolites, Antineoplastic; D007377:Interleukin-3; C000715470:MAS1 protein, human; C078524:PIXY321 fusion protein, recombinant; D000090063:Proto-Oncogene Mas; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; D003561:Cytarabine; D016178:Granulocyte-Macrophage Colony-Stimulating Factor