Sp-family of transcription factors regulates human SHIP2 gene expression

Nutrigenomics of inward rectifier potassium channels

Inwardly rectifying potassium (Kir) channels play a key role in maintaining the resting membrane potential and supporting potassium homeostasis. There are many variants of Kir channels, which are usually tetramers in which the main subunit has two trans-membrane helices attached to two N- and C-terminal cytoplasmic tails with a pore-forming loop in between that contains the selectivity filter. These channels have domains that are strongly modulated by molecules present in nutrients found in different diets, such as phosphoinositols, polyamines and Mg²⁺. These molecules can impact these channels directly or indirectly, either allosterically by modulation of enzymes or via the regulation of channel expression. A particular type of these channels is coupled to cell metabolism and inhibited by ATP (KATP channels, essential for insulin release and for the pathogenesis of metabolic diseases like diabetes mellitus). Genomic changes in Kir channels have a significant impact on metabolism, such as conditioning the nutrients and electrolytes that an individual can take. Thus, the nutrigenomics of ion channels is an important emerging field in which we are attempting to understand how nutrients and diets can affect the activity and expression of ion channels and how genomic changes in such channels may be the basis for pathological conditions that limit nutrition and electrolyte intake. In this contribution we briefly review Kir channels, discuss their nutrigenomics, characterize how different components in the diet affect their function and expression, and suggest how their genomic changes lead to pathological phenotypes that affect diet and electrolyte intake.

Decreased Sp1 Expression Mediates Downregulation of SHIP2 in Gastric Cancer Cells

Past studies have shown that the Src homology 2-containing inositol 5-phosphatase 2 (SHIP2) is commonly downregulated in gastric cancer, which contributes to elevated activation of PI3K/Akt signaling, proliferation and tumorigenesis of gastric cancer cells. However, the mechanisms underlying the reduced expression of SHIP2 in gastric cancer remain unclear. While gene copy number variation analysis and exon sequencing indicated the absence of genomic alterations of SHIP2, bisulfite genomic sequencing (BGS) showed promoter hypomethylation of SHIP2 in gastric cancer cells. Analysis of transcriptional activity of SHIP2 promoter revealed Specificity protein 1 (Sp1) was responsible for the regulation of SHIP2 expression in gastric cancer cells. Furthermore, Sp1 expression, but not Sp3, was frequently downregulated in gastric cancer compared with normal gastric mucosa, which was associated with a paralleled reduction in SHIP2 levels in gastric cancer. Moreover, overexpression of Sp1 inhibited cell proliferation, induced apoptosis, suppressed cell motility and invasion in gastric cancer cells in vitro, which was, at least in part, due to transcriptional activation of SHIP2 mediated by Sp1, thereby inactivating Akt. Collectively, these results indicate that decreased expression of transcription factor Sp1 contributes to suppression of SHIP2 in gastric cancer cells.

Association of SH-2 containing inositol 5'-phosphatase 2 gene polymorphisms and hyperglycemia

OBJECTIVES

SH-2 containing inositol 5'-phosphatase 2 (SHIP2) is a family of inositol 5'-phosphatases, which possess the 5'-phosphatase activity that hydrolyzes phosphatidylinositol-3, 4, 5-trisphosphate to phosphatidylinositol-3, 4-bisphosphate and is suspected to negatively regulates the metabolic signaling of insulin. To clarify the possible involvement of SHIP2 in physiological abnormalities, we examined the human SHIP2 gene polymorphism in a Japanese cohort.

METHODS

We searched single-nucleotide polymorphisms (SNPs) on the human SHIP2 gene promoter and 5'-untranslated region (5'-UTR) and investigated their relationship with impaired fasting glycemia (IFG) in a Japanese cohort. Next, the effect of the SNPs on promoter activity was examined in HeLa and HL60 cells.

RESULTS

Among the several SNPs detected on the human SHIP2 gene promoter and 5'-UTR, 3 SNPs (-405 C/A, +57 G/A, and +334 C/T) formed the haplotypes CGC and AAT and were found at a relatively high frequency in the Japanese population. The frequency of genotypes (+334 CT and TT) was significantly higher in the group with IFG than in the normal group (P < 0.0001, odds ratio = 2.23, 95% confidence interval = 1.50-3.32). This association was not affected by age and gender. Furthermore, one haplotype (+57 A, +334 T) which was inserted into a luciferase reporter plasmid and existed more frequently in the IFG group than in the normal group exhibited increased promoter activity in the culture cells compared with the other haplotype (+57 G, +334 C).

CONCLUSIONS

The SNPs in the SHIP2 gene promoter and the 5'-UTR may account partly for the IFG and may be a marker for the risk of diabetes.