Inhibition of phosphatidylcholine synthesis induces expression of the endoplasmic reticulum stress and apoptosis-related protein CCAAT/enhancer-binding protein-homologous protein (CHOP/GADD153)

Abstract

Inhibition of de novo synthesis of phosphatidylcholine (PC) by some anti-cancer drugs such as hexadecylphosphocholine leads to apoptosis in various cell lines. Likewise, in MT58, a mutant Chinese hamster ovary (CHO) cell line containing a thermo-sensitive mutation in CTP:phosphocholine cytidylyltransferase (CT), an important regulatory enzyme in the CDP-choline pathway, inhibition of PC synthesis causes PC depletion. Cellular perturbations like metabolic insults and unfolded proteins can be registered by the endoplasmic reticulum (ER) and result in ER stress responses, which can lead eventually to apoptosis. In this study we investigated the effect of PC depletion on the ER stress response and ER-related proteins. Shifting MT58 cells to the non-permissive temperature of 40 degrees C resulted in PC depletion via an inhibition of CT within 24 h. Early apoptotic features appeared in several cells around 30 h, and most cells were apoptotic within 48 h. The temperature shift in MT58 led to an increase of pro-apoptotic CCAAT/enhancer-binding protein-homologous protein (CHOP; also known as GADD153) after 16 h, to a maximum at 24 h. Incubation of wild-type CHO-K1 or CT-expressing MT58 cells at 40 degrees C did not induce differences in CHOP protein levels in time. In contrast, expression of the ER chaperone BiP/GRP78, induced by an increase in misfolded/unfolded proteins, and caspase 12, a protease specifically involved in apoptosis that results from stress in the ER, did not differ between MT58 and CHO-K1 cells in time when cultured at 40 degrees C. Furthermore, heat-shock protein 70, a protein that is stimulated by accumulation of abnormal proteins and heat stress, displayed similar expression patterns in MT58 and K1 cells. These results suggest that PC depletion in MT58 induces the ER-stress-related protein CHOP, without raising a general ER stress response.

The novel choline kinase inhibitor ICL-CCIC-0019 reprograms cellular metabolism and inhibits cancer cell growth

“…Caspase-3/7-mediated apoptosis was seen following 48 h treatment with varying concentrations of ICL-CCIC-0019 in HCT116, HUH-7 and MDA-MB-468 cells (Figure 3B). Depletion of PC was previously shown to induce ER stress [26]. Therefore, the expression of ER stress response markers was investigated.…”

Knockdown of triglyceride synthesis does not enhance palmitate lipotoxicity or prevent oleate-mediated rescue in rat hepatocytes

“…The ER membrane typically contains unsaturated phosphatidylcholine (PC) as its major phospholipid component [41], and its composition is tightly regulated: even small changes in fatty acyl composition may induce ER stress. Exogenous saturated fatty acids have been shown to rapidly incorporate into phospholipids of the ER membrane and alter its structure through increased order and reduced fluidity [7, 35, 37, 42], which may explain why markers of ER stress appear rapidly after treatment with PA but not OA [7, 35].…”

Choline kinase inhibition induces exacerbated endoplasmic reticulum stress and triggers apoptosis via CHOP in cancer cells

“…32, 56 Furthermore, ER stress can activate transmembrane proteins located in the ER membrane like IRE1 α and PERK, which inhibit general protein synthesis and activate the non-canonical apoptosis response. ChoKIs dramatically increase GRP78, IRE1 α and CHOP, which suggests that the exacerbated induction of ER stress response depends on ChoK α protein presence in the cells, and the levels of ChoK α are crucial for the ER stress-mediated apoptosis by these inhibitors.…”