title: Mechanism of 4-HPR-induced apoptosis in glioma cells: evidences suggesting role of mitochondrial-mediated pathway and endoplasmic reticulum stress.
abstract: 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 (Delta Psi(m)). 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 Ca(2+) as well as mitochondrial Ca(2+). Chelation of extracellular Ca(2+) by EGTA did not prevent Ca(2+) 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 Ca(2+) from ER by heparin inhibited apoptosis, indicating the role of depletion of Ca(2+) 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.
authors: Department of Endocrinology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Raebareli Road, Lucknow, 226 014, India.
authors: Meenakshi
authors: M
authors: Tiwari
authors: Ashok
authors: A
authors: Kumar
authors: Rohit Anthony
authors: RA
authors: Sinha
authors: Ashutosh
authors: A
authors: Shrivastava
authors: Anil Kumar
authors: AK
authors: Balapure
authors: Ramesh
authors: R
authors: Sharma
authors: Virendra Kumar
authors: VK
authors: Bajpai
authors: Kalyan
authors: K
authors: Mitra
authors: Satish
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authors: Babu
authors: Madan Madhav
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