Molecular mechanisms of deguelin-induced apoptosis in transformed human bronchial epithelial cells

Response of Non–Small Cell Lung Cancer Cells to the Inhibitors of Phosphatidylinositol 3-Kinase/Akt- and MAPK Kinase 4/c-Jun NH2-Terminal Kinase Pathways: An Effective Therapeutic Strategy for Lung Cancer

PURPOSE

We previously showed that phosphatidylinositol 3-kinase (PI3K)/Akt and mitogen-activated protein kinase (MAPK) pathways cooperate to promote non-small cell lung cancer (NSCLC) cell proliferation in vitro. This study was designed to explore whether inhibition of these pathways effectively inhibits NSCLC tumor growth in vivo.

EXPERIMENTAL DESIGN

The effects of PI3K/Akt inhibitors {LY294002, adenoviruses expressing dominant-negative mutant of the p85alpha adaptor subunit of PI3K (Ad-dnp85alpha), dominant-negative Akt [Ad-HA-Akt(KM)], or PTEN (Ad-PTEN)}, MKK4/c-jun NH2-terminal kinase (JNK) inhibitor [SP600215, adenovirus expressing dominant-negative MKK4, Ad-MKK4(KR)], and their combinations on proliferation and apoptosis in NSCLC cells were tested in vitro and in vivo using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, a flow cytometry-based terminal deoxynucleotidyl transferase-mediated nick-end labeling assay, Western blot and immunohistochemical analyses, and an NSCLC xenograft tumor model.

RESULTS

Ad-dnp85alpha significantly inhibited proliferation of a subset of NSCLC cell lines used in our study. Intratumoral injection of Ad-dnp85alpha induced a significant decrease in the growth of H1299 NSCLC xenograft tumors. Concurrent inhibition of the PI3K/Akt and MKK4/JNK pathways showed enhanced antiproliferative effects on H1299 cells in vitro and in vivo by increasing apoptosis.

CONCLUSIONS

PI3K/Akt and MKK4/JNK pathways cooperate to stimulate NSCLC cell proliferation by maintaining cell survival, suggesting that simultaneously targeting these two pathways might be an effective therapeutic strategy against NSCLC.

The activation of Akt/PKB signaling pathway and cell survival

Akt/PKB is a serine/threonine protein kinase that functions as a critical regulator of cell survival and proliferation. Akt/PKB family comprises three highly homologous members known as PKBalpha/Akt1, PKBbeta/Akt2 and PKBgamma/Akt3 in mammalian cells. Similar to many other protein kinases, Akt/PKB contains a conserved domain structure including a specific PH domain, a central kinase domain and a carboxyl-terminal regulatory domain that mediates the interaction between signaling molecules. Akt/PKB plays important roles in the signaling pathways in response to growth factors and other extracellular stimuli to regulate several cellular functions including nutrient metabolism, cell growth, apoptosis and survival. This review surveys recent developments in understanding the molecular mechanisms of Akt/PKB activation and its roles in cell survival in normal and cancer cells.