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Concomitant inactivation of the epidermal growth factor receptor, phosphatidylinositol 3‐kinase/Akt and Janus tyrosine kinase 2/signal transducer and activator of transcription 3 signalling pathways in cardiotoxin III‐treated A549 cells
Author(s) -
Su JungChen,
Lin KueiLi,
Chien ChingMing,
Chuang PeiWen,
Chang LongSen,
Lin ShinneRen
Publication year - 2010
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1111/j.1440-1681.2010.05397.x
Subject(s) - protein kinase b , microbiology and biotechnology , biology , signal transduction , janus kinase , tyrosine phosphorylation , epidermal growth factor , stat3 , chemistry , biochemistry , receptor
Summary 1. Cardiotoxin (CTX) III, a basic polypeptide with 60 amino acid residues isolated from Naja naja atra venom, has potential anticancer therapeutic activity. The aim of the present study was to investigate the apoptotic effect (and the underlying mechanism of action) of CTX III in human adenocarcinoma A549 cells. 2. It was found that CTX III induces apoptosis in A549 cells, as indicated by an increase in the sub‐G 1 population, phosphatidylserine externalization, loss of mitochondrial membrane potential (Ψ m ) with cytochrome c release and activation of caspases 9 and 3. These actions were correlated with upregulation of Bax and Bad and downregulation of various anti‐apoptotic proteins, including Bcl‐2, Bcl‐X L , Mcl‐1, X‐linked inhibitor of apoptosis protein (XIAP) and p‐Bad in CTX III‐treated cells. 3. The signal transduction pathways involved in the effects of CTX III in A549 cells were evaluated using 5 μmol/L AG1478, an inhibitor of the epidermal growth factor receptor (EGFR), and exposing cells to the drug for 8 h. The results indicated that CTX III suppresses phosphorylation of EGFR and activation of phosphatidylinositol 3‐kinase (PI3‐K)/Akt and Janus tyrosine kinase (JAK) 2/signal transducer and activator of transcription (STAT) 3, all of which are downstream molecules in the EGFR signalling pathway. 4. Exposure of cells for 8 h to the PI3‐K inhibitor wortmannin (10 μmol/L) blocked JAK2 and STAT3 activation, whereas exposure of cells to the JAK2 inhibitor AG490 (5 μmol/L) decreased levels of phosphorylated (p‐) JAK2 and p‐STAT3 without affecting PI3‐K/Akt activation. These observations suggest that PI3‐K is an upstream activator of JAK2/STAT3. Furthermore, 5 μmol/L AG490 and 10 μmol/L wortmannin treatment of A549 cells for 8 h resulted in upregulation of Bax and Bad and downregulation of Bcl‐2, Bcl‐X L , XIAP and p‐Bad. 5. Together, the results of the present study indicate that CTX III induces apoptosis in A549 cells by inactivating the EGFR, PI3‐K/Akt and JAK2/STAT3 signalling pathways.