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Niacin activates the PI3K/Akt cascade via PKC- and EGFR-transactivation-dependent pathways through hydroxyl-carboxylic acid receptor 2.

ABSTRACT: Niacin has been demonstrated to activate a PI3K/Akt signaling cascade to prevent brain damage after stroke and UV-induced skin damage; however, the underlying molecular mechanisms for HCA2-induced Akt activation remain to be elucidated. Using CHO-K1 cells stably expressing HCA2 and A431 cells, a human epidermoid cell line with high levels of endogenous expression of functional HCA2 receptors, we first demonstrated that niacin induced a robust Akt phosphorylation at both Thr308 and Ser473 in a time-dependent fashion, with a maximal activation at 5 min and a subsequent reduction to baseline by 30 min through HCA2, and that the activation was significantly blocked by pertussis toxin. The HCA2-mediated activation of Akt was also significantly inhibited by the PKC inhibitors GF109203x and Go6983 in both cell lines, by the PDGFR-selective inhibitor tyrphostin A9 in CHO-HCA2 cells and by the MMP inhibitor GM6001 and EGFR-specific inhibitor AG1478 in A431 cells. These results suggest that the PKC pathway and PDGFR/EGFR transactivation pathway play important roles in HCA2-mediated Akt activation. Further investigation indicated that PI3K and the G?? subunit were likely to play an essential role in HCA2-induced Akt activation. Moreover, Immunobloting analyses using an antibody that recognizes p70S6K1 phosphorylated at Thr389 showed that niacin evoked p70S6K1 activation via the PI3K/Akt pathway. The results of our study provide new insight into the signaling pathways involved in HCA2 activation.

SUBMITTER: Sun H

PROVIDER: S-EPMC4223033 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Niacin activates the PI3K/Akt cascade via PKC- and EGFR-transactivation-dependent pathways through hydroxyl-carboxylic acid receptor 2.

Sun Huawang H Li Guo G Zhang Wenjuan W Zhou Qi Q Yu Yena Y Shi Ying Y Offermanns Stefan S Lu Jianxin J Zhou Naiming N

PloS one 20141106 11

Niacin has been demonstrated to activate a PI3K/Akt signaling cascade to prevent brain damage after stroke and UV-induced skin damage; however, the underlying molecular mechanisms for HCA2-induced Akt activation remain to be elucidated. Using CHO-K1 cells stably expressing HCA2 and A431 cells, a human epidermoid cell line with high levels of endogenous expression of functional HCA2 receptors, we first demonstrated that niacin induced a robust Akt phosphorylation at both Thr308 and Ser473 in a ti ...[more]

PMID: 25375133

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Project description:Mutational activation of the epidermal growth factor receptor (EGFR) is a major player in the pathogenesis of non-small cell lung cancer (NSCLC). NSCLC patients with constitutively active EGFR mutations eventually develop drug resistance against EGFR tyrosine-kinase inhibitors; therefore, better understandings of key components of mutant EGFR (mtEGFR) signaling are required. Here, we initially observed aberrantly high expression of protein kinase C? (PKC?) in lung adenocarcinomas, especially those with EGFR mutations, and proceeded to examine the role of PKC? in the regulation of the signaling pathways downstream of mtEGFR. The results showed that NSCLC cell lines with constitutively active EGFR mutations tend to have very or moderately high PKC? levels. Furthermore, PKC? was constitutively activated in HCC827 and H4006 cells which have an EGFR deletion mutation in exon 19. Interestingly, mtEGFR was not required for the induction of PKC? at protein and message levels suggesting that the increased levels of PKC? are due to independent selection. On the other hand, mtEGFR activity was required for robust activation of PKC?. Loss of functions studies revealed that the NSCLC cells rely heavily on PKC? for the activation of the mTORC1 signaling pathway. Unexpectedly, the results demonstrated that PKC? was required for activation of Akt upstream of mTOR but only in cells with the mtEGFR and with the increased expression of PKC?. Functionally, inhibition of PKC? in HCC827 led to caspase-3-dependent apoptosis and a significant decrease in cell survival in response to cellular stress induced by serum starvation. In summary, the results identified important roles of PKC? in regulating mTORC1 activity in lung cancer cells, whereby a primary switching occurs from PKC?-independent to PKC?-dependent signaling in the presence of EGFR mutations. The results present PKC? as a potential synergistic target of personalized treatment for NSCLC with constitutively active mutant forms of EGFR and constitutively active PKC?.

Dataset Information

Niacin activates the PI3K/Akt cascade via PKC- and EGFR-transactivation-dependent pathways through hydroxyl-carboxylic acid receptor 2.

Publications

Niacin activates the PI3K/Akt cascade via PKC- and EGFR-transactivation-dependent pathways through hydroxyl-carboxylic acid receptor 2.

Similar Datasets

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