DEPTOR promotes survival of cervical squamous cell carcinoma cells and its silencing induces apoptosis through downregulating PI3K/AKT and by up-regulating p38 MAP kinase
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Kalanghad Puthankalam Srinivas1, Remadevi Viji1, Vipin Mohan Dan1, Indira Sukumaran Sajitha1, Rajappan Prakash1, Puthan Valappil Rahul1, Thankayyan R. Santhoshkumar1, Subhadra Lakshmi2, Madhavan Radhakrishna Pillai1
1Cancer Research Program, Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram-695014, Kerala, India
2Division of Cancer Research, Regional Cancer Centre, Thiruvananthapuram-695011, Kerala, India
Madhavan Radhakrishna Pillai, e-mail: firstname.lastname@example.org
Keywords: DEPTOR, cervical cancer, PI3K/AKT, ERK and p38, apoptosis
Received: February 08, 2016 Accepted: March 02, 2016 Published: March 16, 2016
DEPTOR is an endogenous inhibitor of mTOR complexes, de-regulated in cancers. The present study reveals a vital role for DEPTOR in survival of cervical squamous cell carcinoma (SCC). DEPTOR was found to be overexpressed in both cervical SCC cells and tissues and it’s silencing in cervical SCC cells induced apoptosis, mainly by up-regulation of p38 MAPK and by inhibiting PI3K/AKT pathway via a feed-back inhibition from mTORC1-S6K. DEPTOR silencing resulted in reduced expression of the nitric oxide synthases iNOS and eNOS, as well as increased activation of ERK1/2 and p38 MAP kinases. Activation of AKT signaling by overexpression of constitutively active-AKT (CA-AKT) failed to overcome the apoptosis caused by DEPTOR silencing. Similarly pharmacological inhibition of ERK also failed to control apoptosis. However pharmacological inhibition of p38 MAPK rescued the cells from apoptosis, indicating the major role of p38 MAPK in cell death induced by DEPTOR silencing. DEPTOR was also found to regulate ERK1/2 in an AKT dependent manner. DEPTOR knockdown induced cell death in SiHa cells overexpressing the anti-apoptotic Bcl-2 and Bcl-xL, indicating strong survival role of DEPTOR in these cells. DEPTOR overexpression activated PI3K/AKT by relieving the negative feed-back inhibition from mTORC1-S6K. DEPTOR regulation was also observed to be independent of HPV E6/E7 oncoproteins, but it might be a molecular co-factor contributing to cervical carcinogenesis. In summary, DEPTOR is found to promote survival of cervical SCC cells and its reduction induced apoptosis via differential effects on PI3K/AKT and p38 MAPK and can be a potential target in cervical SCC.
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