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RAFTK/PYK2-dependent and -independent apoptosis in multiple myeloma cells
D Chauhan1, T Hideshima, P Pandey
1Department of Adult Oncology, Dana Farber Cancer Institute, Harvard Medical School, Boston, MA 02115, USA.
Abstract:
Related Adhesion Focal Tyrosine Kinase (RAFTK; also known as Pyk2), is a member of the Focal Adhesion Kinase (FAK) subfamily and is activated by TNF alpha, UV light and increases in intracellular calcium levels. However, the function of RAFTK remains largely unknown. Our previous studies demonstrated that treatment with dexamethasone (Dex), ionizing radiation (IR), and anti-Fas mAb induces apoptosis in multiple myeloma (MM) cells. In the present study, we examined the potential role of RAFTK during induction of apoptosis in human MM cells triggered by these three stimuli. Dex-induced apoptosis, in contrast to apoptosis triggered by anti-Fas mAb or IR, is associated with activation of RAFTK. Transient overexpression of RAFTK wild type (RAFTK WT) induces apoptosis, whereas transient overexpression of Kinase inactive RAFTK (RAFTK K-M) blocks Dex-induced apoptosis. In contrast, transient overexpression of RAFTK K-M has no effect on apoptosis triggered by IR or Fas. In Dex-resistant cells, Dex does not trigger either RAFTK activation or apoptosis. Finally, interleukin-6 (IL-6), a known survival factor for MM cells, inhibits both activation of RAFTK and apoptosis of MM.1S cells triggered by Dex. Our studies therefore demonstrate Dex-induced RAFTK-dependent, and IR or Fas induced RAFTK-independent apoptotic signaling cascades in MM cells.
Insights
Related Adhesion Focal Tyrosine Kinase (RAFTK) plays a role in dexamethasone-induced apoptosis in multiple myeloma cells. RAFTK activation is specific to dexamethasone treatment, unlike IR or Fas-induced apoptosis.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Related Adhesion Focal Tyrosine Kinase (RAFTK), also known as Pyk2, is part of the Focal Adhesion Kinase (FAK) subfamily.
- RAFTK is activated by TNF alpha, UV light, and increased intracellular calcium, but its precise function is largely unknown.
- Dexamethasone (Dex), ionizing radiation (IR), and anti-Fas mAb induce apoptosis in multiple myeloma (MM) cells.
Purpose of the Study:
- To investigate the role of RAFTK in apoptosis induction in human MM cells by Dex, IR, and anti-Fas mAb.
- To determine if RAFTK signaling is involved in the apoptotic pathways triggered by these stimuli.
Main Methods:
- Transient overexpression of wild-type RAFTK (RAFTK WT) and kinase-inactive RAFTK (RAFTK K-M) in MM cells.
- Assessing apoptosis induction and RAFTK activation in response to Dex, IR, and anti-Fas mAb.
- Examining RAFTK activation and apoptosis in Dex-resistant MM cells and the effect of IL-6.
Main Results:
- Dex-induced apoptosis is associated with RAFTK activation, unlike apoptosis induced by anti-Fas mAb or IR.
- Overexpression of RAFTK WT promotes apoptosis, while RAFTK K-M inhibits Dex-induced apoptosis.
- RAFTK K-M had no effect on IR- or Fas-induced apoptosis, and Dex failed to activate RAFTK or induce apoptosis in Dex-resistant cells.
- Interleukin-6 (IL-6) inhibited both RAFTK activation and Dex-induced apoptosis in MM.1S cells.
Conclusions:
- Dex-induced apoptosis in MM cells involves a RAFTK-dependent signaling pathway.
- IR- or Fas-induced apoptosis in MM cells proceeds through RAFTK-independent pathways.
- RAFTK activation is a specific marker for Dex-induced apoptosis in multiple myeloma.