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Abstract
Calreticulin (CRT) is a high-capacity Ca2+ protein whose expression is up-regulated during cellular transformation and is associated with disease progression in multiple types of malignancies. At the same time, CRT has been characterized as an important stress-response protein capable of inducing immunogenic cell death (ICD) when translocated to the cell surface. It remains unclear why CRT expression is preserved by malignant cells during the course of transformation despite its immunogenic properties. In this study, we identify a novel, critical function of CRT as a cell survival factor in multiple types of human solid-tissue malignancies. CRT knockdown activates p53, which mediates cell-death response independent of executioner caspase activity and accompanied full-length poly ADP ribose polymerase (PARP) cleavage. Mechanistically, we show that down-regulation of CRT results in mitochondrial Ca2+ overload and induction of mitochondria permeability transition pore (mPTP)-dependent cell death, which can be significantly rescued by the mPTP inhibitor, Cyclosporin A (CsA). The clinical importance of CRT expression was revealed in the analysis of the large cohort of cancer patients (N = 2,058) to demonstrate that high levels of CRT inversely correlates with patient survival. Our study identifies intracellular CRT as an important therapeutic target for tumors whose survival relies on its expression.
Highlights
Calreticulin (CRT) is a multifunctional stress-response chaperone residing mainly in the lumen of the endoplasmic reticulum (ER) in the cell with the ability to control proper protein folding and regulate cellular adhesion [1,2,3,4,5,6]
The resulting growth curves revealed the significant reduction in the proliferative rate of short hairpin RNA targeting Calreticulin (shCRT)-transduced melanoma cells compared with the control-transduced counterparts independent of the BRAF_V600 status (Fig 1C)
We reveal that CRT plays a major role in the cancer cell survival, and its down-regulation induces a nonapoptotic type of cell death, independent of executioner caspase activity
Summary
Calreticulin (CRT) is a multifunctional stress-response chaperone residing mainly in the lumen of the endoplasmic reticulum (ER) in the cell with the ability to control proper protein folding and regulate cellular adhesion [1,2,3,4,5,6]. The link between CRT and carcinogenesis has mainly been characterized at the level of correlation between augmented CRT expression and disease progression. Studies of multiple solid tumors originating from the skin (melanoma), breast, pancreas, liver, and colon demonstrated that the CRT expression levels were positively correlated with advanced tumor stages and lymph node metastasis [3, 6,7,8]. Calreticulin is Required for Cancer Cell Survival. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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