hKSR-2, a vitamin D-regulated gene, inhibits apoptosis in arabinocytosine-treated HL60 leukemia cells.

Abstract

Ras signaling can be modulated by the scaffolding activity of kinase suppressor of Ras-1 (KSR-1) and by the hKSR-2 protein, resulting in diverse phenotypic outcomes. The mitogen-activated protein kinase cascade downstream from Ras and KSRs includes Raf-1 and extracellular signal-regulated kinase 1/2 kinases, known to enhance survival potential of a range of cell types. Because the molecular events that increase survival of HL60 cells induced to differentiate toward monocytic phenotype by 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] are not known, we investigated if KSR proteins provide a survival function in these cells. We found that whereas kinase suppressor of Ras-1 had no detectable effect on cell survival in the system studied here, 1,25-(OH)2D3-induced up-regulation of hKSR-2 enhanced the resistance of HL60 cells to arabinocytosine. Knockdown of hKSR-2 by either small interfering RNA or antisense oligonucleotides increased arabinocytosine-induced apoptosis, which was accompanied by reduced Bcl-2/Bax and Bcl-2/Bad ratios, and increased caspase-3 activating cleavage. In contrast, up-regulation of Mcl-1 was not abrogated by anti-sense (AS) AS-hKSR-2, pointing to a specific role of Bcl-2 in control of 1,25-(OH)2D3-induced increased cell survival. These findings are consistent with the previously shown lack of fully differentiated monocytic cells in HL60 cultures exposed to 1,25-(OH)2D3 in which hKSR-2 was knocked down, suggesting that optimal differentiation of these cells requires enhanced antiapoptotic mechanisms provided, at least in part, by hKSR-2. Collectively, these results suggest that hKSR-2 may offer a new target for novel therapies of acute myelogenous leukemia.

• Authors: Xuening Wang, Rahul Patel, George P Studzinski
• Journal: Molecular cancer therapeutics (Mol Cancer Ther) Vol. 7 Issue 9 Pg. 2798-806 (Sep 2008) ISSN: 1535-7163 [Print] United States
• PMID: 18790760 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Adaptor Proteins, Signal Transducing
• Antioxidants
• CNKSR2 protein, human
• Myeloid Cell Leukemia Sequence 1 Protein
• Oligonucleotides, Antisense
• Proto-Oncogene Proteins c-bcl-2
• RNA, Messenger
• RNA, Small Interfering
• dihydroxy-vitamin D3
• Cytarabine
• Vitamin D
• Acetylcysteine

Topics

• Acetylcysteine (pharmacology)
• Adaptor Proteins, Signal Transducing (antagonists & inhibitors, genetics, metabolism)
• Antioxidants (pharmacology)
• Apoptosis (drug effects)
• Cytarabine (toxicity)
• Gene Expression Regulation, Neoplastic (drug effects)
• HL-60 Cells
• Humans
• Myeloid Cell Leukemia Sequence 1 Protein
• Necrosis
• Oligonucleotides, Antisense (pharmacology)
• Proto-Oncogene Proteins c-bcl-2 (metabolism)
• RNA, Messenger (genetics, metabolism)
• RNA, Small Interfering (metabolism)
• Vitamin D (analogs & derivatives, metabolism, pharmacology)