Mechanism of 4-HPR-induced apoptosis in glioma cells: evidences suggesting role of mitochondrial-mediated pathway and endoplasmic reticulum stress

• Published in: Carcinogenesis (New York) 2006-10, Vol.27 (10), p.2047-2058
• Main Authors: Tiwari, Meenakshi, Kumar, Ashok, Sinha, Rohit Anthony, Shrivastava, Ashutosh, Balapure, Anil Kumar, Sharma, Ramesh, Bajpai, Virendra Kumar, Mitra, Kalyan, Babu, Satish, Godbole, Madan Madhav
• Format: Article
• Language: English
• Subjects: Alitretinoin; Animals; Antineoplastic Agents - pharmacology; Apoptosis - drug effects; Apoptosis Inducing Factor - metabolism; Biological and medical sciences; Calcium - metabolism; Carcinogenesis, carcinogens and anticarcinogens; Cell Line, Tumor; Cytochromes c - metabolism; Endoplasmic Reticulum - metabolism; Fenretinide - pharmacology; Glioma - drug therapy; Glioma - pathology; Humans; Medical sciences; Mitochondria - physiology; Mitochondrial Membrane Transport Proteins - physiology; Mitochondrial Permeability Transition Pore; Neurology; Rats; Reactive Oxygen Species - metabolism; Receptors, Retinoic Acid - genetics; Retinoic Acid Receptor gamma; Retinoid X Receptor alpha - genetics; Tretinoin - pharmacology; Tumors; Tumors of the nervous system. Phacomatoses
• ISSN: 0143-3334; 1460-2180
• DOI: 10.1093/carcin/bgl051

N-(4-Hydroxyphenyl)retinamide (4-HPR), a synthetic retinoid is under clinical evaluation as a therapeutic agent in a variety of cancers. Its mechanism(s) of action involves multiple overlapping pathways that still remain unclear. In glioma cells its mechanism of action is not well elucidated. Here, we show that 4-HPR and not all-trans retinoic acid and 9-cis retinoic acid effectively induce apoptosis in glioma cells. 4-HPR-induced apoptosis is associated with hydroperoxide production and loss of mitochondrial membrane potential (ΔΨm). Ultrastructural changes further indicate 4-HPR-induced mitochondrial swelling, endoplasmic reticulum (ER) dilation as well as close proximity of mitochondria and ER. As suggested by dilated ER, 4-HPR treatment increased the free cytosolic Ca2+ as well as mitochondrial Ca2+. Chelation of extracellular Ca2+ by EGTA did not prevent Ca2+ elevation, thus suggesting involvement of intracellular calcium stores in the release. Buffering of intracellular calcium by BAPTA-AM did not prevent 4-HPR-induced apoptosis; however, blocking the release of Ca2+ from ER by heparin inhibited apoptosis, indicating the role of depletion of Ca2+ from ER stores in apoptosis. 4-HPR treatment also resulted in an increase in Bax levels along with its translocation to mitochondria that promote mitochondrial membrane permeabilization. 4-HPR-induced apoptosis was further associated with the release of cytochrome c and apoptosis-inducing factor (AIF) from mitochondria to cytosol and nucleus, respectively, along with caspase-3 and caspase-7 activation. However, AIF nuclear translocation, peripheral chromatin condensation and apoptosis were not completely prevented by general caspase inhibitors, thus suggesting involvement of a caspase-dependent and caspase-independent pathway in 4-HPR-induced apoptosis. Taken together, these results suggest the role of mitochondrial-mediated pathway and ER stress as a key event in 4-HPR-induced apoptosis in glioma cells.