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Spectral Confocal Imaging of Fluorescently tagged Nicotinic Receptors in Knock-in Mice with Chronic Nicotine Administration
Published on: February 10, 2012
Nicotine induces multi-site phosphorylation of Bad in association with suppression of apoptosis
Zhaohui Jin1, Fengqin Gao, Tammy Flagg
1Shands Cancer Center and Department of Medicine, University of Florida, Gainesville, Florida 32610-0232, USA.
Abstract:
Nicotine is an important component in cigarette smoke that can activate the growth-promoting pathways to facilitate the development of lung cancer. However, the intracellular mechanism(s) by which nicotine promotes survival of lung cancer cells remains enigmatic. Bad is a proapoptotic BH3-only member of the Bcl2 family and is expressed in both small cell lung cancer and non-small cell lung cancer cells. Here we report that nicotine potently induces Bad phosphorylation at Ser112, Ser136, and Ser155 in a mechanism involving activation of MAPKs ERK1/2, PI3K/AKT, and PKA in human lung cancer cells. Nicotine-induced multi-site phosphorylation of Bad results in sequestering Bad from mitochondria and subsequently interacting with 14-3-3 in the cytosol. Treatment of cells with PKC inhibitor (staurosporine), MEK-specific inhibitor (PD98059), PI3 kinase inhibitor (LY294002), or PKA inhibitor (H89) blocks the nicotine-induced Bad phosphorylation that is associated with enhanced apoptotic cell death. The fact that beta-adrenergic receptor inhibitor (propranolol) blocks nicotine-induced activation of ERK1/2, AKT, PKA, Bad phosphorylation, and cell survival suggests that nicotine-induced Bad phosphorylation may occur through the upstream beta-adrenergic receptors. The fact that specific knockdown of Bad expression by RNA interference using short interfering RNA enhances cell survival and that nicotine has no additional survival effect on these cells suggests that Bad may act as a required target of nicotine. Thus, nicotine-induced survival may occur in a mechanism through multi-site phosphorylation of Bad, which may lead to development of human lung cancer and/or chemoresistance.
Insights
Nicotine promotes lung cancer cell survival by phosphorylating the Bad protein, inhibiting its cell death function. This mechanism, involving specific signaling pathways and beta-adrenergic receptors, highlights Bad as a key target in nicotine-induced cancer development.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Nicotine in cigarette smoke promotes lung cancer development.
- The precise intracellular mechanisms of nicotine-driven lung cancer cell survival are unclear.
- Bad, a proapoptotic protein, is present in both small cell and non-small cell lung cancer cells.
Purpose of the Study:
- To elucidate the intracellular mechanisms by which nicotine promotes lung cancer cell survival.
- To investigate the role of Bad protein phosphorylation in nicotine-induced cell survival.
- To identify signaling pathways involved in nicotine's effects on lung cancer cells.
Main Methods:
- Utilized human lung cancer cell lines.
- Investigated nicotine-induced phosphorylation of Bad at multiple sites (Ser112, Ser136, Ser155).
- Examined the involvement of MAPK/ERK1/2, PI3K/AKT, and PKA signaling pathways.
- Assessed the impact of specific kinase inhibitors (staurosporine, PD98059, LY294002, H89) and a beta-adrenergic receptor inhibitor (propranolol).
- Employed RNA interference for specific Bad gene knockdown.
Main Results:
- Nicotine induces multi-site phosphorylation of Bad, sequestering it in the cytosol via 14-3-3 interaction.
- This phosphorylation is mediated by the activation of ERK1/2, PI3K/AKT, and PKA pathways.
- Inhibitors of these pathways, along with beta-adrenergic receptor blockade, block nicotine-induced Bad phosphorylation and promote apoptosis.
- Knockdown of Bad expression enhances cell survival, rendering nicotine's effect non-additive.
- Nicotine-induced survival is dependent on Bad phosphorylation, suggesting Bad is a critical target.
Conclusions:
- Nicotine promotes lung cancer cell survival through multi-site phosphorylation of the proapoptotic protein Bad.
- This process involves the activation of ERK1/2, PI3K/AKT, and PKA signaling pathways, potentially initiated by beta-adrenergic receptors.
- Bad acts as a crucial mediator of nicotine's survival effects in lung cancer cells.
- Understanding this mechanism could inform strategies against lung cancer development and chemoresistance.
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