Nutrition Guide

SK3 is a small-conductance calcium-activated potassium channel partly responsible for the calcium-dependent after hyperpolarisation current (IAHP). It belongs to a family of channels known as small-conductance potassium channels, which consists of three members – SK1, SK2 and SK3 (KCNN1, 2 and 3 respectively), which share a 60-70% sequence identity.[1] These channels have acquired a number of alternative names, however a NC-IUPHAR has recently achieved consensus on the best names, KCa2.1 (SK1), KCa2.2 (SK2) and KCa2.3 (SK3).[2] Small conductance channels are responsible for the medium and possibly the slow components of the IAHP.

KCa2.3 channels play a major role in human physiology, particularly in smooth muscle relaxation. The expression level of KCa2.3 channels in the endothelium influences arterial tone by setting arterial smooth muscle membrane potential. The sustained activity of KCa2.3 channels induces a sustained hyperpolarisation of the endothelial cell membrane potential, which is then carried to nearby smooth muscle through gap junctions.[5] Blocking the KCa2.3 channel or suppressing KCa2.3 expression causes a greatly increased tone in resistance arteries, producing an increase in peripheral resistance and blood pressure.

The SK channel family contains 4 members - SK1, SK2, SK3, and SK4.

Mutations in KCa2.3 are suspected to be a possible underlying cause for several neurological disorders, including schizophrenia, bipolar disorder, Alzheimer’s disease, anorexia nervosa and ataxia[6][7][8] as well as myotonic muscular dystrophy.

KCa2.3 contains 6 transmembrane domains, a pore-forming region, and intracellular N- and C- termini[3][1] and is readily blocked by apamin. The gene for KCa2.3, KCNN3, is located on chromosome 1q21.

All SK channels can be pharmacologically blocked by quaternary ammonium salts of a plant-derived neurotoxin bicuculline.[6] In addition, SK channels(SK1-SK3) are sensitive to blockade by the bee venom apamin, [7] but SK4 (IK) is not. and the scorpion venom tamapin.[8]

HSP60 has been shown to influence apoptosis in tumor cells which seems to be associated with a change in expression levels. There is some inconsistency in that some research shows a positive expression while other research shows a negative expression, and it seems to depend on the type of cancer. There are different hypotheses to explain the effects of positive versus negative expression. Positive expression seems to inhibit “apoptotic and necrotic cell death” while negative expression is thought to play a part “in activation of apoptosis”.[16][17] As well as influencing apoptosis, HSP60 changes in expression level have been shown to be

Pyridoxal phosphate has been implicated in increasing or decreasing the expression of certain genes. Increased intracellular levels of the vitamin will lead to a decrease in the transcription of glucocorticoid hormones. Also, vitamin B6 deficiency will lead to the increased expression of albumin mRNA. Also, pyridoxal phosphate will influence gene expression of glycoprotein IIb by interacting with various transcription factors. The result is inhibition of platelet aggregation.[2]

Changes in expression of discrete VGF fragments have been detected in different neurological and psychiatric conditions. In schizophrenia, one study has shown an increase in the VGF23-62 peptide[6] and a subsequent small study demonstrated that drugs further increase the expression, pointing at a possible ameliorating action of the fragment. A decreased expression of VGF26-62 peptide was found in frontotemporal dementia[7] and the expression of a fragment containing aminoacids 378-398 was found to be changing in amyotrophic lateral sclerosis[8] and Alzheimer’s disease.[

The expression of this protein is required for the transcription of a subset of class II major histocompatibility genes.[4] Furthermore Xbp1 heterodimerizes with other bZIP transcription factors such as c-fos.[4] Xbp1 expression is controlled by the cytokine IL-4 and the antibody IGHM.[5] Xbp1 in turn controls the expression of IL-6 which promotes plasma cell growth and of immunoglobulins in B lymphocytes.[5]

While hPLSCR1, 3 and 4 are expressed in a variety of tissues with few exceptions, expression of hPLSCR2 is only restricted to the testis. hPLSCR4 is not expressed in peripheral blood lymphocytes, whereas hPLSCR1 and 3 were not detected in the brain.[4] However, the functional significance of this differential gene expression is not yet understood. While the gene and the mRNA of hPLSCR5 provide evidence of its existence, the protein has yet to be described in the literature.

While the expression of LXR? and LXR? in various tissues somewhat overlap, the tissue distribution pattern of these two isoforms overall differ considerably. LXR? expression is restricted to liver, kidney, intestine, fat tissue, macrophages, lung, and spleen and is highest in liver, hence the name liver X receptor ? (LXR?). LXR? is expressed in almost all tissues and organs, hence the early name UR (ubiquitous receptor).[7] The different pattern of expression suggests that LXR? and LXR? have different roles in regulating physiological function.

Because MTs play an important role in transcription factor regulation, problems with MT function or expression may lead to malignant transformation of cells and ultimately cancer. Studies have found increased expression of MTs in some cancers of the breast, colon, kidney, liver, lung, nasopharynx, ovary, prostate, mouth, salivary gland, testes, thyroid and urinary bladder; they have also found lower levels of MT expression in hepatocellular carcinoma and liver adenocarcinoma. There is evidence to suggest that higher levels of MT expression may also lead to resistance to chemotherapeutic drugs.

The expression of AhRR is high in testis, lung, ovary, spleen and pancreas in adults, whereas expression is low in all tissues in fetuses.[5]

Agents shown to induce Thy1 expression include: Thymopoietin, thymosin, prostaglandins, nerve growth factor, IL-1, TNF, PMA, Ca2+ ionophore, and diacylglycerol (DAG).[9]

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