Characterization of Calcium Release-activated Apoptosis of LNCaP Prostate Cancer Cells

Abstract

Apoptosis inhibition rather than enhanced cellular proliferation occurs in prostate cancer (CaP), the most commonly diagnosed malignancy in American men. Therefore, it is important to characterize residual apoptotic pathways in CaP cells. When Apoptosis is the physiological counterbalance to mitosis and a fundamental mechanism for achieving tissue homeostasis (1). Accordingly, disorders of apoptosis contribute to a number of disease states. Degenerative conditions, such as Alzheimer's disease and AIDS, occur in the setting of excess apoptosis, whereas hyperplastic diseases, including cancer, often occur when apoptosis is attenuated (2). Specifically, inhibition of apoptosis rather than enhanced cellular proliferation is the more critical pathophysiological insult that contributes to the development of prostatic adenocarcinoma (CaP) 1 (3, 4). CaP is the most commonly diagnosed malignancy in American men and is the second most common cause of death due to cancer, with estimates that 37,000 men died from CaP in 1999 (5). Successful CaP therapies have been shown to induce tumor regression via apoptosis; however, therapy-resistant cells fail to die in response to treatment (6). It is therefore important to characterize the residual functional apoptotic pathways in therapy-resistant CaP cells. Perturbation of calcium ion (Ca 2ϩ ) homeostasis is a common occurrence in CaP cells induced to undergo apoptosis by a variety of agents, including chemotherapeutics (7) and androgen ablation (8,9).Although the influx of Ca 2ϩ across the cell membrane results in a dramatic increase in cytosolic [Ca 2ϩ ], this influx is often invoked by a less readily detectable cytosolic [Ca 2ϩ ] elevation as a consequence of organellar Ca 2ϩ store release (10). For example, the endoplasmic reticulum (ER) serves as an intracellular Ca 2ϩ store that is released into the cytosol in response to a variety of stimuli, including binding of inositol 1,4,5-trisphosphate (IP 3 ) to its cognate ER-localized receptor (IP 3 R) (11). The release of ER Ca 2ϩ stores in turn induces a Ca 2ϩ influx across the plasma membrane, also known as the Ca 2ϩ release-activated Ca 2ϩ current (I CRAC ) (12). Thus, the release of ER Ca 2ϩ stores serves to trigger a larger perturbation in cytosolic [Ca 2ϩ ]. Studies with an IP 3 R-deficient Jurkat T-lymphocyte cell line underscore the importance of ER Ca 2ϩ stores in cellular signaling. In contrast to the parental cell line, these cells are defective in antigen-specific T-cell signaling and are resistant to multiple inducers of apoptosis, including Fas ligand, CD3 antibody, glucocorticoids, and irradiation (13). These results are of interest because Jurkat cells have been used to study the role of caspases in apoptosis. Caspases are aspartate-specific cysteine proteases that constitute the effector arm of cell death (14). Upon receipt of an apoptotic stimulus, large pro-domain initiator caspases (such as caspase-8 and -9) are activated by autoproteolysis, which converts the single polypeptide zymogen to form the activ...

Effect of tauroursodeoxycholic acid on endoplasmic reticulum stress–induced caspase-12 activation

“…38 Cytosolic calcium has been implicated as a proapoptotic second messenger involved in both triggering apoptosis and regulating caspases. 30,37 The role of calcium homeostasis in our experimental model was confirmed by series of experiments showing induction of Bip/GRP78 protein, calpain, and decreased apoptosis after treatment with a calcium cheater. Our results show that elevation of intracellular calcium levels is associated with ER stress-initiated apoptosis by TG leading to caspase-12 activation.…”

“…TG disrupts intracellular calcium homeostasis by increasing cytosolic calcium, inducing ER stress-mediated apoptosis. 30,31,41 We show here that although TG caused dramatic changes in ER architecture, the integrity of mitochondria remained intact. In addition, no loss of MMP was observed after TG treatment.…”

“…30,37,40 It has been shown that Ca ϩϩ release from the ER and/or capacitative Ca ϩϩ influx through Ca ϩϩ release-activated channels are apoptogenic. 30,41 Intracellular calcium level is regulated by a combination of actions of calcium channels, calciumbinding proteins, and sequestration to the ER and other intracellular spaces. TG disrupts intracellular calcium homeostasis by increasing cytosolic calcium, inducing ER stress-mediated apoptosis.…”

“…30,31 We developed a TG-induced ER stress model of apoptosis in a liver-derived cell line and assessed the role of calcium homeostasis and caspase-12. Our data show that TG-induced apoptosis results primarily from activation of caspase-12, as a result of elevation of cytosolic calcium.…”

A Ca2+-dependent signalling circuit regulates influenza A virus internalization and infection

“…S3a). Given that thapsigargin raises [Ca 2 þ ]i by blocking the sarcoendoplasmic reticulum Ca 2 þ ATPases pumps, which thereby causes endoplasmic reticulum stores to become depleted 21 , this result might indicate that intracellular Ca 2 þ released from endoplasmic reticulum is crucial for IAV infection and replication. In contrast, BAPTA-AM remarkably reduced the production of progeny viruses ( Fig.…”