Bcl-xL overexpression inhibits progression of molecular events leading to paclitaxel-induced apoptosis of human acute myeloid leukemia HL-60 cells

• Published in: Cancer research (Chicago, Ill.) Vol. 57; no. 6; pp. 1109 - 1115
• Main Authors: IBRADO, A. M, LIU, L, BHALLA, K
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Association for Cancer Research 15.03.1997
• Subjects: Antineoplastic agents; Apoptosis - drug effects; bcl-2-Associated X Protein; bcl-X Protein; Benzoquinones; Biological and medical sciences; Caspase 3; Caspases; Cell Cycle - drug effects; Cysteine Endopeptidases - metabolism; General aspects; HL-60 Cells - drug effects; Humans; Lactams, Macrocyclic; Medical sciences; Neoplasm Proteins - metabolism; Paclitaxel - pharmacology; Pharmacology. Drug treatments; Phosphorylation - drug effects; Protein Processing, Post-Translational - drug effects; Protein-Serine-Threonine Kinases - metabolism; Proto-Oncogene Proteins - biosynthesis; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins - physiology; Proto-Oncogene Proteins c-bcl-2 - metabolism; Proto-Oncogene Proteins c-raf; Quinones - pharmacology; Recombinant Fusion Proteins - metabolism; Signal Transduction - drug effects; Transfection; Antineoplastic agent; Human; Acute; Gene overexpression; Cytotoxicity; Malignant hemopathy; In vitro; Cell death; Taxane derivatives; Established cell line; Paclitaxel; Mechanism of action; Tumor cell; Apoptosis; Acute myelocytic leukemia
• ISSN: 0008-5472; 1538-7445

Paclitaxel has been shown to activate Raf-1 and cause phosphorylation of Bcl-2, which has been correlated with paclitaxel-induced apoptosis of cancer cells. In the present studies, we demonstrate that in human AML HL-60 cells that express Bcl-2 but little Bcl-xL (HL-60/neo cells), paclitaxel-induced phosphorylation of Bcl-2 is followed by increased intracellular free Bax levels. This, in turn, is followed by the cleavage and activation of the key cysteine protease, CPP32beta/Yama, and cleavage of poly(ADP-ribose) polymerase, resulting in the DNA fragmentation of apoptosis. Cotreatment with the benzoquinone ansamycin Geldanamycin depleted Raf-1 but did not decrease Bcl-2 levels or impair paclitaxel-induced Bcl-2 phosphorylation in HL-60/neo cells. Also, Geldanamycin did not affect paclitaxel-induced apoptosis of HL-60/neo cells. As compared to the control HL-60/neo, HL-60/Bcl-xL cells contain Bcl-2 as well as an enforced overexpression of Bcl-xL. Immunoprecipitation studies with anti-Bcl-2 and/or anti-Bcl-x antibodies demonstrated that HL-60/Bcl-xL cells possess lower free Bax but higher levels of Bax heterodimerized to Bcl-2 and Bcl-xL. Following treatment of HL-60/Bcl-xL cells with paclitaxel, although Bcl-2 phosphorylation was observed, it was not followed by increased free Bax levels, cleavage of CPP32beta/Yama and poly(ADP-ribose) polymerase, or induction of the DNA fragmentation of apoptosis. These findings indicate the order of molecular events leading to paclitaxel-induced apoptosis and show that Raf-1 may not be involved in paclitaxel-induced phosphorylation of Bcl-2 or apoptosis of HL-60 cells.