Human neuronal nicotinic acetylcholine receptor (AChR) alpha4 subunits and an alpha4 mutant (S247Falpha4) found in autosomal-dominant nocturnal frontal lobe epilepsy (ADNFLE) were expressed along with beta2 in permanently transfected tsA201 human embryonic kidney cell lines. Their sensitivity to activation, desensitization, and up-regulation by cholinergic ligands was investigated. Up-regulation after 3 to 24 h resulted primarily from an increase in assembly of AChRs from large pools of unassembled subunits, but up-regulation also resulted from a 5-fold increase in the lifetime of AChRs in the surface membrane. Up-regulation does not require current flow through surface membrane AChRs, because up-regulation occurs in the presence of the channel blocker mecamylamine and with the alpha4 mutant, which prevents nearly all AChR function. Both membrane-permeable ligands like nicotine and much less permeable quaternary amine cholinergic ligands can act as pharmacological chaperones within the endoplasmatic reticulum to promote the assembly of AChRs. Agonists are more potent pharmacological chaperones than antagonists, presumably because activated or desensitized conformations assemble more efficiently. Assembly intermediates are disrupted by solubilization in Triton X-100, but chemical cross-linking stabilizes a putative assembly intermediate approximately the size of an alpha4beta2alpha4beta2 tetramer.

Autoantibodies are frequently observed in healthy individuals. In a minority of these individuals, they lead to manifestation of autoimmune diseases, such as rheumatoid arthritis or Graves' disease. Overall, more than 2.5% of the population is affected by autoantibody-driven autoimmune disease. Pathways leading to autoantibody-induced pathology greatly differ among different diseases, and autoantibodies directed against the same antigen, depending on the targeted epitope, can have diverse effects. To foster knowledge in autoantibody-induced pathology and to encourage development of urgently needed novel therapeutic strategies, we here categorized autoantibodies according to their effects. According to our algorithm, autoantibodies can be classified into the following categories: (1) mimic receptor stimulation, (2) blocking of neural transmission, (3) induction of altered signaling, triggering uncontrolled (4) microthrombosis, (5) cell lysis, (6) neutrophil activation, and (7) induction of inflammation. These mechanisms in relation to disease, as well as principles of autoantibody generation and detection, are reviewed herein.

Nicotinic acetylcholine receptors (AChRs) containing ␣6 subunits are typically found at aminergic nerve endings where they play important roles in nicotine addiction and Parkinson's disease. ␣6* AChRs usually contain ␤3 subunits. ␤3 subunits are presumed to assemble only in the accessory subunit position within AChRs where they do not participate in forming acetylcholine binding sites. Assembly of subunits in the accessory position may be a critical final step in assembly of mature AChRs. Human ␣6 AChRs subtypes were permanently transfected into human tsA201 human embryonic kidney (HEK) cell lines. ␣6␤2␤3 and ␣6␤4␤3 cell lines were found to express much larger amounts of AChRs and were more sensitive to nicotine-induced increase in the amount of AChRs than were ␣6␤2 or ␣6␤4 cell lines. The increased sensitivity to nicotineinduced up-regulation was due not to a ␤3-induced increase in affinity for nicotine but probably to a direct effect on assembly of AChR subunits. HEK cells express only a small amount of mature ␣6␤2 AChRs, but many of these subunits are on the cell surface. This contrasts with Xenopus laevis oocytes, which express a large amount of incorrectly assembled ␣6␤2 subunits that bind cholinergic ligands but form large amorphous intracellular aggregates. Monoclonal antibodies (mAbs) were made to the ␣6 and ␤3 subunits to aid in the characterization of these AChRs. The ␣6 mAbs bind to epitopes C-terminal of the extracellular domain. These data demonstrate that both cell type and the accessory subunit ␤3 can play important roles in ␣6* AChR expression, stability, and up-regulation by nicotine.

The main immunogenic region (MIR) is a conformation-dependent region at the extracellular apex of ␣1 subunits of muscle nicotinic acetylcholine receptor (AChR) that is the target of half or more of the autoantibodies to muscle AChRs in human myasthenia gravis and rat experimental autoimmune myasthenia gravis. By making chimeras of human ␣1 subunits with ␣7 subunits, both MIR epitopes recognized by rat mAbs and by the patient-derived human mAb 637 to the MIR were determined to consist of two discontiguous sequences, which are adjacent only in the native conformation. The MIR, including loop ␣1 67-76 in combination with the N-terminal ␣ helix ␣1 1-14, conferred high-affinity binding for most rat mAbs to the MIR. However, an additional sequence corresponding to ␣1 15-32 was required for high-affinity binding of human mAb 637. A water soluble chimera of Aplysia acetylcholine binding protein with the same ␣1 MIR sequences substituted was recognized by a majority of human, feline, and canine myasthenia gravis sera. The presence of the ␣1 MIR sequences in ␣1/␣7 chimeras greatly promoted AChR expression and significantly altered the sensitivity to activation. This reveals a structural and functional, as well as antigenic, significance of the MIR.

Iron, an indispensable element for life, is involved in all kinds of important physiological activities. Iron promotes cell growth and proliferation, but it also causes oxidative stress damage. The body has a strict regulation mechanism of iron metabolism due to its potential toxicity. As a cancer of the bone marrow and blood cells, leukemia threatens human health seriously. Current studies suggest that dysregulation of iron metabolism and subsequent accumulation of excess iron are closely associated with the occurrence and progress of leukemia. Specifically, excess iron promotes the development of leukemia due to the pro-oxidative nature of iron and its damaging effects on DNA. On the other hand, leukemia cells acquire large amounts of iron to maintain rapid growth and proliferation. Therefore, targeting iron metabolism may provide new insights for approaches to the treatment of leukemia. This review summarizes physiologic iron metabolism, alternations of iron metabolism in leukemia and therapeutic opportunities of targeting the altered iron metabolism in leukemia, with a focus on acute leukemia.