Nuclear And endoplasmic reticulum

Members of the Bcl-2 family share one or more Bcl-2 homology (BFI) domains, named BFI1, BFI2, BFI3, and BFI4 (Adams and Cory, 1998). It is not yet clear which structural features determine if these proteins possess pro- or anti-apoptotic activities. However, some studies revealed that the BH3 domain is a critical domain for the proapoptotic members (Chittenden et al., 1995). Besides BH domains, some contain a hydrophobic domain in the C-terminal region, which is essential for the attachment to intracellular membranes, like the outer mitochondrial, nuclear, and endoplasmic reticulum membranes (Krajewski et al., 1993 Nguyen et al., 1993). 

Fig 24.7. Free radical-mediated cellular injury. Superoxide and the hydroxyl radical initiate lipid jjeroxidation in the cellular, mitochondrial, nuclear, and endoplasmic reticulum membranes. The increase in cellular permeability results in an influx of Ca, which causes further mitochondrial damage. The cysteine sulfhydryl groups and other amino acid residues on proteins are oxidized and degraded. Nuclear and mitochondrial DNA can be oxidized, resulting in strand breaks and other types of damage. RNOS (NO, NO2, and perox5mitrite) have similar effects. 

The nuclear and endoplasmic reticulum membranes are often in continuity therefore, it has been proposed that the nuclear and the endoplasmic reticulum membranes are parts of a single membrane system. It seems imperative to elucidate the relationship between nuclear membrane and endoplasmic reticulum because if the nuclear membrane is only an area of differentiation of the endoplasmic reticulum, it could not be constituted solely of phospholipids but would have a biochemical composition similar to that of the membranes of the endoplasmic reticulum. 

Many of the morphological and biochemical changes that occur in cells that die by necrosis are very different from those that occur in apoptosis. During necrosis cells swell, mitochondria and endoplasmic reticulum lose their structure and become dysfunctional and the nuclear membrane becomes disrupted (Fig. 35-1). Necrotic death is independent of premitochondrial apoptotic proteins such as Bax, cytochrome c release and caspase activation. Necrosis is further distinguished from apoptosis by the fact that necrosis usually occurs as the result of a traumatic physical injury or stroke and cells die en masse, whereas apoptosis typically occurs in individual cells within a population of surviving neighbors. 

The process of infection of lupine nodule cells by Rhizobia was examined by the thin-section electron microscopic technique, as well as the freeze-fracture technique. Different membranes such as infection thread membranes, peribacterioid membranes, plasma membranes, membranes of cytoplasmic vesicles, and membranes of the Golgi bodies and ER were stained with uranium-lead, silver, phosphotungstic acid, and ZIO (31). ZIO stained the membranes of the proximal face of the Golgi bodies and endoplasmic reticulum. ZIO staining has given good contrast in thick sections such as a cotyledon cell, a root cell, and an aleurone layer for ER, dictyosomes cisternae, mitochondria, and nuclear envelopes (17,32-37). 

Swanson, R., Locher, M., and Hochstrasser, M. a conserved ubiquitin ligase of the nuclear envelope/endoplasmic reticulum that functions in both ER-assodated and Mata2 repressor degradation. Genes Dev. 2001, 15, 2660-74. 

To isolate RNA from cellular fractions such as nuclear or cytoplasm, the first step is to isolate that particular cell fraction. During the fractionation process, caution is exercised not to contaminate one fraction with another. The crude nuclear fraction is often contaminated with mitochondria and endoplasmic reticulum, both of which carry their RNA components. Hence it is highly desirable to further purify the nuclear fraction before isolating the RNA. 

Krajewski S, Tanaka S, Takayama S, Schibler MJ, Fenton W, Reed JC (1993), Investigation of the subcellular distribution of the Bcl-2 oncoprotein residence in the nuclear envelope, endoplasmic reticulum, and outer mitochondrial membranes, Cancer Res. 53 4701-4714. 

SREBPs are transcription factors that bind to the sterol regulatory element DNA sequence TCACNCCAC. Unactivated SREBPs are attached to the nuclear envelope and endoplasmic reticulum membranes. In cells with low levels of sterols, SREBPs are cleaved to a water-soluble N-terminal domain that is translocated to the nucleus. These activated SREBPs then bind to specific sterol regulatory element DNA sequences, thus up-regulating the synthesis of enzymes involved in sterol biosynthesis. Sterols in turn inhibit the cleavage of SREBPs and therefore synthesis of additional sterols is reduced through a negative-feedback loop. 

The increase in nuclear cyclin B/CDKl activity promotes phosphorylation of nuclear substrates that are necessary for mitosis, such as nuclear envelope breakdown, spindle formation, chromatin condensation, and restmcturing of the Golgi and endoplasmic reticulum (85, 86). Numerous cyclin B/CDKl substrates have been dehned, which include nuclear lamins, nucleolar proteins, centrosomal proteins, components of the nuclear pore complex, and microtubule-associated proteins (87-89). Cyclin B/CDKl complexes also phosphorylate MCM4 to block replication of DNA, the TFIIH subunit of RNA polymerase II to inhibit transcription, and the ribosomal S6 protein kinase to prevent translation during mitosis (90-92). 

Subramanian, K., and Meyet, T. (1997). Calcium-induced restructuring of nuclear envelope and endoplasmic reticulum calcium stoics. Ced 39, 963-971. 

Under diabetic conditions, oxidative stress and endoplasmic reticulum stress are induced in various tissues [173, 176, 177, 178, 179]. Moreover, the y9-cells have very low levels of antioxidative enzymes, becoming them more susceptible to the stress [172]. ROS can function as signaling molecules to activate a number of cellular stress-sensitive pathways that cause cellular damage, and are ultimately responsible for the late complications of diabetes. Evidence suggests that common stress-activated signaling pathways such as nuclear factor nuclear factor-xB (NF-kB) [180, 181, 182], p38 mitogen-activated protein kinase (MARK) [183], protein kinase C (PKC) [184], toll-like receptors (TLRs) [185, 186], and c-Jun N-terminal kinase (INK) [187 188] underlie the development of these diabetic complications. 

Endothelial cells of brain arteries, veins and capillaries of the Wistar rat showed a positive NADPH-diaphorase (EC 1.6.99.1) reaction in form of 2-(2 -benzothiazolyl) - 5 - styryl - 3 - (4 - phthal - hydrazidyl) tetrazolium chloride-formazan contrast at the nuclear envelope, membranes of mitochondria and endoplasmic reticulum (Stanarius et al. 1997). Endothelial nitric oxide synthase (EC 1.14.23) immu-nostaining without tyramide signal amplification yielded electron dense 3,3 -diaminobenzidine precipitates that were seen in the endothelium if arteries, veins and some capillaries. Its pattern corresponded roughly with the membrane-bound 2-(2 -benzothiazolyl) - 5 - styryl - 3 - (4 - phthal-hydrazidyl) tetrazolium chloride-formazan deposits generated by NADPH-diaphorase. 

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