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A carbazole alkaloid deactivates mTOR through the suppression of rictor and that induces apoptosis in lung cancer cells

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Abstract

Non-small cell lung cancer (NSCLC) is known to be a difficult cancer to treat because of its poor prognosis, limited option for surgery, and resistance to chemo or radiotherapy. In this study, we have demonstrated that suppression of rictor expression in A549 and H1299 NSCLC cells by mahanine, a carbazole alkaloid, disrupted constitutive activation of mTOR and Akt. Mahanine suppression of rictor gene expression and consequent attenuation of its protein expression affected the inhibition of mTOR (Ser-2481) and Akt (Ser-473) phosphorylation. Since mahanine treatment revealed this new insight of rictor-mTOR relationship, we examined an association between mTOR activation with rictor expression. Interestingly, in rictor knockdown (KD) NSCLC cells, mTOR activation was significantly impaired. Transfection of rictor over-expression vector into the NSCLC cells reversed this situation. In fact, both rictor KD and mahanine treated cells showed considerably depleted phospho-mTOR level. These results indicate that rictor is required to maintain constitutive activation of mTOR in lung cancer cells. When mTOR kinase activity in rictor KD cells was examined with Akt as substrate, a significant reduction of Akt phosphorylation indicated impairment of mTOR kinase potentiality. Disruption of mTOR and Akt activation caused drastic mortality of NSCLC cancer cells through apoptosis. Hence, our study reveals a new dimension in mTOR-rictor relationship, where rictor stands to be a suitable therapeutic target for lung cancer.

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Abbreviations

NSCLC:

Non-small cell lung cancer

Rictor:

Rapamycin insensitive companion of mTOR

mTOR:

Mammalian target of rapamycin

mTORC2:

Mammalian target of rapamycin complex 2

KD:

Knock down

p-Akt:

Phosphorylated Akt

PDK-1:

PI3K-dependent kinase-1

DMEM:

Dulbecco’s-modified Eagle’s medium

FBS:

Fetal bovine serum

DMSO:

Dimethyl sulfoxide

ASO:

Antisense oligonucleotide

Q-PCR:

Quantitative PCR

FITC:

Fluorescein isothiocyanate

MTT:

3-(4,5-dimethylthiazol-2-yl)-2-5- diphenyltetrazolium bromide

PBS:

Phosphate-buffered saline

Fhit:

Fragile histidine triad

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Acknowledgments

We thank Dr. Partha P. Banerjee (Georgetown University Medical Center, Washington, DC, USA) for providing the A549 cell line and Dr. Susanta Roychoudhury, Cancer Biology Division, CSIR-IICB, Kolkata for H1299 cell line. This research work was financially supported by the grant from CSIR-NEEP Project (HCP-005) and Department of Science and Technology, New Delhi (VI-D&P/289/08-09/TDT). SB expresses his gratitude to NASI, Allahabad for the award of Senior Scientist fellowship. The technical help from Mr. Hemanta Jadav and Mr. Kali Charan Nayek of Visva-Bharati is greatly appreciated.

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The authors declare that there are no conflicts of interest.

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    Authors and Affiliations

    1. Department of Zoology, School of Life Science, Visva-Bharati University, Santiniketan, 731235, India

      Priyajit Chatterjee, Soma Seal, Sandip Mukherjee, Rakesh Kundu, Santi Prasad Sinha Babu & Samir Bhattacharya

    2. CSIR- North East Institute of Science & Technology, Jorhat, 785006, Assam, India

      Mantu Bhuyan, Nabin C. Barua, Pranab K. Baruah & Samir Bhattacharya

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    1. Priyajit Chatterjee
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    Correspondence to Samir Bhattacharya.

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    Priyajit Chatterjee and Soma Seal have equally contributed to this work.

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    Chatterjee, P., Seal, S., Mukherjee, S. et al. A carbazole alkaloid deactivates mTOR through the suppression of rictor and that induces apoptosis in lung cancer cells. Mol Cell Biochem 405, 149–158 (2015). https://doi.org/10.1007/s11010-015-2406-2

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