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Articles by Victor Chi in JoVE
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İmmünohistokimya: Parafin Bölüm Vektör Labs Vectastain ABC Seti
Department of Physiology and Biophysics, University of California, Irvine (UCI)
Other articles by Victor Chi on PubMed
Human Liver Cytochrome P450 2D6 Genotype, Full-length Messenger Ribonucleic Acid, and Activity Assessed with a Novel Cytochrome P450 2D6 Substrate
The goal of this study was to develop and validate a cytochrome P450 (CYP) 2D6 probe substrate with improved sensitivity to elucidate the relationship of CYP2D6 ribonucleic acid transcript levels, genotype, and enzyme activity in human liver biopsy samples.
The D-diastereomer of ShK Toxin Selectively Blocks Voltage-gated K+ Channels and Inhibits T Lymphocyte Proliferation
The polypeptide toxin ShK is a potent blocker of Kv1.3 potassium channels, which are crucial in the activation of human effector memory T cells (T(EM)); selective blockers constitute valuable therapeutic leads for the treatment of autoimmune diseases mediated by T(EM) cells, such as multiple sclerosis, rheumatoid arthritis, and type-1 diabetes. The critical motif on the toxin for potassium channel blockade consists of neighboring lysine and tyrosine residues. Because this motif is sufficient for activity, an ShK analogue was designed based on D-amino acids. D-allo-ShK has a structure essentially identical with that of ShK and is resistant to proteolysis. It blocked Kv1.3 with K(d) 36 nm (2,800-fold lower affinity than ShK), was 2-fold selective for Kv1.3 over Kv1.1, and was inactive against other K(+) channels tested. D-allo-ShK inhibited human T(EM) cell proliferation at 100-fold higher concentration than ShK. Its circulating half-life was only slightly longer than that of ShK, implying that renal clearance is the major determinant of its plasma levels. D-allo-ShK did not bind to the closed state of the channel, unlike ShK. Models of D-allo-ShK bound to Kv1.3 show that it can block the pore as effectively as ShK but makes different interactions with the vestibule, some of which are less favorable than for native ShK. The finding that an all-D analogue of a polypeptide toxin retains biological activity and selectivity is highly unusual. Being resistant to proteolysis and nonantigenic, this analogue should be useful in K(+) channel studies; all-d analogues with improved Kv1.3 potency and specificity may have therapeutic advantages.
Store-dependent and -independent Modes Regulating Ca2+ Release-activated Ca2+ Channel Activity of Human Orai1 and Orai3
We evaluated currents induced by expression of human homologs of Orai together with STIM1 in human embryonic kidney cells. When co-expressed with STIM1, Orai1 induced a large inwardly rectifying Ca(2+)-selective current with Ca(2+)-induced slow inactivation. A point mutation of Orai1 (E106D) altered the ion selectivity of the induced Ca(2+) release-activated Ca(2+) (CRAC)-like current while retaining an inwardly rectifying I-V characteristic. Expression of the C-terminal portion of STIM1 with Orai1 was sufficient to generate CRAC current without store depletion. 2-APB activated a large relatively nonselective current in STIM1 and Orai3 co-expressing cells. 2-APB also induced Ca(2+) influx in Orai3-expressing cells without store depletion or co-expression of STIM1. The Orai3 current induced by 2-APB exhibited outward rectification and an inward component representing a mixed calcium and monovalent current. A pore mutant of Orai3 inhibited store-operated Ca(2+) entry and did not carry significant current in response to either store depletion or addition of 2-APB. Analysis of a series of Orai1-3 chimeras revealed the structural determinant responsible for 2-APB-induced current within the sequence from the second to third transmembrane segment of Orai3. The Orai3 current induced by 2-APB may reflect a store-independent mode of CRAC channel activation that opens a relatively nonselective cation pore.
Imaging of Effector Memory T Cells During a Delayed-type Hypersensitivity Reaction and Suppression by Kv1.3 Channel Block
Effector memory T (Tem) cells are essential mediators of autoimmune disease and delayed-type hypersensitivity (DTH), a convenient model for two-photon imaging of Tem cell participation in an inflammatory response. Shortly (3 hr) after entry into antigen-primed ear tissue, Tem cells stably attached to antigen-bearing antigen-presenting cells (APCs). After 24 hr, enlarged Tem cells were highly motile along collagen fibers and continued to migrate rapidly for 18 hr. Tem cells rely on voltage-gated Kv1.3 potassium channels to regulate calcium signaling. ShK-186, a specific Kv1.3 blocker, inhibited DTH and suppressed Tem cell enlargement and motility in inflamed tissue but had no effect on homing to or motility in lymph nodes of naive and central memory T (Tcm) cells. ShK-186 effectively treated disease in a rat model of multiple sclerosis. These results demonstrate a requirement for Kv1.3 channels in Tem cells during an inflammatory immune response in peripheral tissues. Targeting Kv1.3 allows for effector memory responses to be suppressed while central memory responses remain intact.
Kv1.3 Potassium Channels As a Therapeutic Target in Multiple Sclerosis
We discuss the potential use of inhibitors of Kv1.3 potassium channels in T lymphocytes as therapeutics for multiple sclerosis. Current treatment strategies target the immune system in a non-selective manner. The resulting general immunosuppression, toxic side-effects and increased risk of opportunistic infections create the need for more selective therapeutics. Autoreactive effector-memory T (T(EM)) cells, considered to be major mediators of autoimmunity, express large numbers of Kv1.3 channels. Selective blockers of Kv1.3 inhibit calcium signaling, cytokine production and proliferation of T(EM) cells in vitro, and T(EM) cell-motility in vivo. Kv1.3 blockers ameliorate disease in animal models of multiple sclerosis, rheumatoid arthritis, type 1 diabetes mellitus and contact dermatitis without compromising the protective immune response to acute infections. Kv1.3 blockers have a good safety profile in rodents and primates.
Potassium Channel Modulation by a Toxin Domain in Matrix Metalloprotease 23
Peptide toxins found in a wide array of venoms block K(+) channels, causing profound physiological and pathological effects. Here we describe the first functional K(+) channel-blocking toxin domain in a mammalian protein. MMP23 (matrix metalloprotease 23) contains a domain (MMP23(TxD)) that is evolutionarily related to peptide toxins from sea anemones. MMP23(TxD) shows close structural similarity to the sea anemone toxins BgK and ShK. Moreover, this domain blocks K(+) channels in the nanomolar to low micromolar range (Kv1.6 > Kv1.3 > Kv1.1 = Kv3.2 > Kv1.4, in decreasing order of potency) while sparing other K(+) channels (Kv1.2, Kv1.5, Kv1.7, and KCa3.1). Full-length MMP23 suppresses K(+) channels by co-localizing with and trapping MMP23(TxD)-sensitive channels in the ER. Our results provide clues to the structure and function of the vast family of proteins that contain domains related to sea anemone toxins. Evolutionary pressure to maintain a channel-modulatory function may contribute to the conservation of this domain throughout the plant and animal kingdoms.
Development of a Sea Anemone Toxin As an Immunomodulator for Therapy of Autoimmune Diseases
Electrophysiological and pharmacological studies coupled with molecular identification have revealed a unique network of ion channels-Kv1.3, KCa3.1, CRAC (Orai1 + Stim1), TRPM7, Cl(swell)-in lymphocytes that initiates and maintains the calcium signaling cascade required for activation. The expression pattern of these channels changes during lymphocyte activation and differentiation, allowing the functional network to adapt during an immune response. The Kv1.3 channel is of interest because it plays a critical role in subsets of T and B lymphocytes implicated in autoimmune disorders. The ShK toxin from the sea anemone Stichodactyla helianthus is a potent blocker of Kv1.3. ShK-186, a synthetic analog of ShK, is being developed as a therapeutic for autoimmune diseases, and is scheduled to begin first-in-man phase-1 trials in 2011. This review describes the journey that has led to the development of ShK-186.
