Distinct apoptotic responses imparted by c-myc and max.
The c-myc oncoprotein accelerates programmed cell death (apoptosis) after growth factor deprivation or pharmacological insult in many cell lines. We have shown that max, the obligate c-myc heterodimeric partner protein, also promotes apoptosis after serum withdrawal in NIH3T3 fibroblasts or cytokine deprivation in interleukin-3 (IL-3)-dependent 32D murine myeloid cells. We now show that c-myc- and max-overexpressing 32D cells differ in the nature of their apoptotic responses after IL-3 removal or treatment with chemotherapeutic compounds. In the presence of IL-3, c-myc overexpression enhances the sensitivity of 32D cells to Etoposide (Sigma, St Louis, MO), Adriamycin (Pharmacia, Columbus, OH), and Camptothecin (Sigma), whereas max overexpression increases sensitivity only to Camptothecin. Drug treatment of c-myc-overexpressing cells in the absence of IL-3 did not alter the spectrum of drug sensitivity other than to additively accelerate cell death. In contrast, enhanced sensitivity to Adriamycin, Etoposide, and Taxol (Bristol-Meyers Squibb, Princeton, NJ) was revealed in max-overexpressing cells concurrently deprived of IL-3. Differential rates of apoptosis were not strictly correlated with the ability of the drugs to promote G1 or G2/M arrest. Ectopic expression of Bcl-2 or Bcl-XL blocked drug-induced apoptosis in both cell lines. In contrast, whereas Bcl-2 blocked apoptosis in both cell lines in response to IL-3 withdrawal, Bcl-XL blocked apoptosis in max-overexpressing cells but not in c-myc-overexpressing cells. These results provide mechanistic underpinnings for the idea that c-myc and max modulate distinct apoptotic pathways.
Section of Hematology/Oncology, the Department of Pediatrics, Children's Hospital of Pittsburgh, Pittsburgh, PA, USA.
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Prochownik
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D001491:Basophils / Q000166:cytology / Q000187:drug effects; D002166:Camptothecin / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D016895:Culture Media, Serum-Free; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D019281:Dimerization; D004317:Doxorubicin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D005047:Etoposide / Q000494:pharmacology; D016259:Genes, myc; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects*; D007377:Interleukin-3 / Q000494:pharmacology; D008407:Mast Cells / Q000166:cytology / Q000187:drug effects; D051379:Mice; D055503:Protein Multimerization; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D016271:Proto-Oncogene Proteins c-myc / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000378:metabolism / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014162:Transfection; D051020:bcl-X Protein
D000970:Antineoplastic Agents; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; C494812:Bcl2l1 protein, mouse; D016895:Culture Media, Serum-Free; D004268:DNA-Binding Proteins; D007377:Interleukin-3; C067850:Myc associated factor X; D019253:Proto-Oncogene Proteins c-bcl-2; D016271:Proto-Oncogene Proteins c-myc; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D051020:bcl-X Protein; C068422:Max protein, mouse; D005047:Etoposide; D004317:Doxorubicin; D002166:Camptothecin