The immune system provides good models for cell death, a phenomenon now recognized to be of fundamental importance in many fields of biology. Cell death is strikingly polymorphic: it can proceed via necrosis (as in complement-mediated cell death) or apoptosis, but the latter displays different patterns (in the receptor-mediated death of some thymocytes, in cell death mediated by TNF alpha or by cytotoxic T cells), perhaps reflecting different pathways of control of a common core mechanism. Even though there are differences in the morphological and metabolic changes associated with the different patterns of apoptosis, some recurrent sequences of events are observed in almost all dying cells. The metabolic state of a cell often seems to play a major role in determining if and how this cell will die in given external circumstances. The nature of molecules causally involved in the dying cell can now be approached in some systems.

Cell Death Mechanisms and the Immune System

When cultured hepatocytes were incubated in cell culture medium at 4°C for up to 30 h and then returned to 37°C, blebbing of the plasma membrane, cell detachment, chromatin condensation and margination, enhanced nuclear stainability with Hoechst 33342, ruffling of the nuclear membrane, and DNA fragmentation occurred. Similar to hepatocytes, cultured liver endothelial cells exhibited blebbing, chromatin condensation and margination, marked nuclear condensation, and increased stainability with Hoechst 33342 when exposed to hypothermia/rewarming. In both cell types, the occurrence and extent of these alterations were dependent on the duration of the cold incubation period. This cold-induced apoptosis was inhibited by hypoxia, by an array of free radical scavengers/antioxidants, and by iron chelators. However, the extent of the protection by the different antioxidants was different in the two cell types: iron chelators provided complete protection in liver endothelial cells but only partial protection in hepa...

Cold-induced apoptosis in cultured hepatocytes and liver endothelial cells: mediation by reactive oxygen species.

Bleomycin (BLM), a compound currently used in anticancer therapy, is unable to cross the plasma membrane efficiently. Electropermeabilization allows a defined number of BLM molecules to enter directly into the cell cytoplasm. Such a procedure has revealed that BLM is intrinsicly highly cytotoxic. Here we show that the mechanisms of the cell death caused by BLM are closely related to the number of BLM molecules introduced into the cell cytoplasm. When only a few thousand BLM molecules are internalized, cells display an arrest in the G2-M phase of the cell cycle and become enlarged and polynucleated before dying. These observations parallel the “mitotic death” seen with ionizing radiations. By contrast, when several million molecules of BLM are internalized, morphological changes identical to those usually associated with apoptosis are observed as well as very rapid DNA fragmentation into oligonucleosomal-sized fragments. We demonstrate that this fragmentation, which occurs within a few seconds after BLM internalization, is consistent with the direct internucleosomal cleavage of chromatin by BLM. Our findings reinforce the importance of DNA digestion as an early and essential step in the morphological changes associated with apoptosis.

https://cancerres.aacrjournals.org/content/canres/53/22/5462.full.pdf

Bleomycin, an Apoptosis-mimetic Drug That Induces Two Types of Cell Death Depending on the Number of Molecules Internalized

Compared to bacteria and plants, the cold shock response has attracted little attention in mammals except in some areas such as adaptive thermogenesis, cold tolerance, storage of cells and organs, and recently, treatment of brain damage and protein production. At the cellular level, some responses of mammalian cells are similar to microorganisms; cold stress changes the lipid composition of cellular membranes, and suppresses the rate of protein synthesis and cell proliferation. Although previous studies have mostly dealt with temperatures below 20°C, mild hypothermia (32°C) can change the cell’s response to subsequent stresses as exemplified by APG-1, a member of the HSP110 family. Furthermore, 32°C induces expression of CIRP (cold-inducible RNAbinding protein), the first cold shock protein identified in mammalian cells, without recovery at 37°C. Remniscent of HSP, CIRP is also expressed at 37°C and developmentary regulated, possibly working as an RNA chaperone. Mammalian cells are metabolically active at 32°C, and cells may survive and respond to stresses with different strategies from those at 37°C. Cellular and molecular biology of mammalian cells at 32°C is a new area expected to have considerable implications for medical sciences and possibly biotechnology.

/pdf/cold-shock-response-in-mammalian-cells-36yo7r51ok.pdf

Cold Shock Response in Mammalian Cells

Castration initiates extensive apoptosis of the secretory epithelial cells lining the ducts of the rat ventral prostate, resulting in the striking regression of this male sexual accessory tissue. We had previously described the paradox of finding similar cascades of gene activity (c-fos greater than c-myc greater than hsp-70) induced during the early period of ventral prostate regression and during the regrowth of the ventral prostate gland initiated by testosterone replenishment. This common pattern of protooncogene expression during periods of predominant cellular apoptosis or proliferation caused us to examine further the possibility that the two cellular events occur through identical early molecular pathways. In the present study we demonstrate that apoptotic prostate epithelial cells incorporate bromodeoxyuridine into nuclear high-molecular-weight DNA prior to nuclear DNA fragmentation. The DNA synthetic activity occurs in coordination with a massive induction of proliferative cell nuclear antigen, a proliferation marker, in the nuclei of androgen-deprived prostatic epithelial cells. Moreover, this activity is also associated with the increased expression of mRNA encoding p53, a suppressor gene well known as a cell cycle-blocking agent. Our data indicate that quiescent (G0) prostate epithelial cells undergo apoptosis due to two sequential events initiated by testosterone depletion. The first event is the active reentry of these cells into the cell cycle. The second event is the apoptotic destruction resulting from the inability of the differentiated cells to successfully complete this cycle.

https://cancerres.aacrjournals.org/content/canres/52/16/4313.full.pdf

Hormone-regulated apoptosis results from reentry of differentiated prostate cells onto a defective cell cycle.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2890%2980040-P

Giorgo Bellomo

Papers

Calcium-dependent DNA fragmentation in human synovial cells exposed to cold shock