Role of XIAP in inhibiting cisplatin-induced caspase activation in non-small cell lung cancer cells: A small molecule Smac mimic sensitizes for chemotherapy-induced apoptosis by enhancing caspase-3 activation

• Published in: Experimental cell research Vol. 313; no. 6; pp. 1215 - 1224
• Main Authors: Checinska, Agnieszka, Hoogeland, Bas S.J., Rodriguez, Jose A., Giaccone, Giuseppe, Kruyt, Frank A.E.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-04-2007; Elsevier BV
• Subjects: Antineoplastic Agents - pharmacology; Apoptosis; Binding sites; Carcinoma, Non-Small-Cell Lung - drug therapy; Carcinoma, Non-Small-Cell Lung - metabolism; Caspase 3 - metabolism; Caspase 9 - metabolism; Caspase 9 - physiology; Cell Line, Tumor; Cellular biology; Cisplatin - pharmacology; Cisplatin-based chemotherapy; Down-Regulation; Enzyme Activation; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Neoplastic; Humans; Inhibitor drugs; Inhibitor of Apoptosis Proteins - metabolism; Intracellular Signaling Peptides and Proteins - physiology; Lung cancer; Lung Neoplasms - drug therapy; Lung Neoplasms - metabolism; Mitochondrial Proteins - physiology; Models, Biological; RNA Interference; Signal Transduction; Smac; X-Linked Inhibitor of Apoptosis Protein - metabolism; X-Linked Inhibitor of Apoptosis Protein - physiology; XIAP; XIAP; Smac; Lung cancer; Cisplatin-based chemotherapy
• ISSN: 0014-4827; 1090-2422
• DOI: 10.1016/j.yexcr.2006.12.011

X-linked IAP (XIAP) suppresses apoptosis by binding to initiator caspase-9 and effector caspases-3 and -7. Smac/DIABLO that is released from mitochondria during apoptosis can relieve its inhibitory activity. Here we investigated the role of XIAP in the previously found obstruction of chemotherapy-induced caspase-9 activation in non-small cell lung cancer (NSCLC) cells. Endogenously expressed XIAP bound active forms of both caspase-9 and caspase-3. However, downregulation of XIAP using shRNA or disruption of XIAP/caspase-9 interaction using a small molecule Smac mimic were unable to
significantly induce caspase-9 activity, indicating that despite a strong binding potential of XIAP to caspase-9 it is not a major determinant in blocking caspase-9 in NSCLC cells. Although unable to revert caspase-9 blockage, the Smac mimic was able to enhance cisplatin-induced apoptosis, which was accompanied by increased caspase-3 activity. Additionally, a more detailed analysis of caspase activation in response to cisplatin indicated a reverse order of activation, whereby caspase-3 cleaved caspase-9 yielding an inactive form. Our findings indicate that the use of small molecule Smac mimic, when combined with an apoptotic trigger, may have therapeutic potential for the treatment of NSCLC.