Paraptosome: A Novel Pathological Feature in Paraptotic Cell Death

Abstract

Paraptosis is a novel form of programmed cell death characterized by distinct morphological features such as swelling of the endoplasmic reticulum and mitochondria, and cytoplasmic vacuolation. Unlike apoptosis, paraptosis does not involve the activation of caspases or DNA fragmentation. These unique features make paraptosis an intriguing target for cancer therapy, particularly against apoptosis-resistant cells. Here, we report a novel morphological feature of paraptosis: the formation of high-density spherical structure, which we tentatively term “paraptosome.” We found that these putative paraptosomes originate from the Golgi apparatus, appearing as high-density formations under light microscopy and colocalizing with the trans-Golgi marker β4GALT1-RFP. Time-lapse confocal microscopy and immunostaining demonstrated that putative paraptosomes form due to Golgi stress or disintegration, leading to severe disruption of Golgi function. Furthermore, we show that paraptosis inducers such as glabridin, morusin, and honokiol can cause significant alterations in the endoplasmic reticulum, mitochondria, autophagosomes, and lysosomes in U251MG glioblastoma cells; however, the formation of putative paraptosomes is not induced by isolated stress inducers. Collectively, these findings suggest that the putative paraptosome may be a novel characteristic structure of paraptosis. The discovery of paraptosomes provides a unique marker for defining paraptotic cell death and offers new insights into the characteristic pathological phenomena associated with multiple organelle dysfunction. This finding broadens the scope of cell biology research by introducing a new structural paradigm linked to paraptosis and may have implications for developing targeted therapies against apoptosis-resistant cancers.