Diverse patterns of cell-specific gene expression in response to glucocorticoid in the developing small intestine

SGK1, autophagy and cancer: an overview

BACKGROUND

The serum and glucocorticoid-induced kinase-1 (SGK1) belonging to the AGC protein kinase family phosphorylates serine and threonine residues of target proteins. It regulates numerous ion channels and transporters and promotes survival under cellular stress. Unique to SGK1 is a tight control at transcriptional and post-transcriptional levels. SGK1 regulates multiple signal transduction pathways related to tumor development. Several studies have reported that SGK1 is upregulated in different types of human malignancies and induces resistance against inhibitors, drugs, and targeted therapies.

RESULTS AND CONCLUSION

This review highlights the cellular functions of SGK1, its crucial role in cancer development, and clinical insights for SGK1 targeted therapies. Furthermore, the role of SGK1-mediated autophagy as a potential therapeutic target for cancer has been discussed.

Serum and Glucocorticoid Regulated Kinase 1 in Sodium Homeostasis

The ubiquitously expressed serum and glucocorticoid regulated kinase 1 (SGK1) is tightly regulated by osmotic and hormonal signals, including glucocorticoids and mineralocorticoids. Recently, SGK1 has been implicated as a signal hub for the regulation of sodium transport. SGK1 modulates the activities of multiple ion channels and carriers, such as epithelial sodium channel (ENaC), voltage-gated sodium channel (Nav1.5), sodium hydrogen exchangers 1 and 3 (NHE1 and NHE3), sodium-chloride symporter (NCC), and sodium-potassium-chloride cotransporter 2 (NKCC2); as well as the sodium-potassium adenosine triphosphatase (Na⁺/K⁺-ATPase) and type A natriuretic peptide receptor (NPR-A). Accordingly, SGK1 is implicated in the physiology and pathophysiology of Na⁺ homeostasis. Here, we focus particularly on recent findings of SGK1’s involvement in Na⁺ transport in renal sodium reabsorption, hormone-stimulated salt appetite and fluid balance and discuss the abnormal SGK1-mediated Na⁺ reabsorption in hypertension, heart disease, edema with diabetes, and embryo implantation failure.

Hydrocortisone-induced anti-inflammatory effects in immature human enterocytes depend on the timing of exposure

The immature human gut has a propensity to exaggerated inflammatory responses that are thought to play a role in the pathogenesis of necrotizing enterocolitis (NEC). Prenatal exposure to corticosteroids has been reported to reduce the risk of NEC, while postnatal dexamethasone treatment is associated with adverse neurodevelopmental outcomes in preterm infants. The aim of this study was to investigate the direct role of hydrocortisone in gene expression patterns and inflammatory responses in immature human enterocytes. Time-dependent hydrocortisone effects in nontransformed primary human fetal intestinal epithelial cell line H4 were investigated by cDNA microarray. Fetal intestinal organ culture and cell culture experiments were conducted. Inflammatory responses were induced by stimulation with IL-1β and TNF-α with and without hydrocortisone. IL-8 and IL-6 expression and secretion were measured as functional readout. Here we report time-dependent hydrocortisone-induced changes in gene expression patterns detected by cDNA microarray. Hydrocortisone significantly attenuated IL-1β-induced inflammatory responses in the immature human gut when administered at the time of the proinflammatory insult: IL-1β-induced IL-8 and IL-6 secretion in the fetal ileum as well as H4 cells were significantly reduced. Hydrocortisone also inhibited IL-8 secretion in response to TNF-α. In contrast, TNF-α-induced IL-8 secretion was not reduced in cells treated with hydrocortisone for 48 h before stimulation. Our observations provide a physiological basis for understanding the differential clinical effects of corticosteroids in the immature human gut depending on the timing of treatment.

An enteral leucine supply modulates human duodenal mucosal proteome and decreases the expression of enzymes involved in fatty acid beta-oxidation

Leucine is well known to regulate protein metabolism in muscle. We recently reported that enteral leucine infusion decreased proteasome activity in human duodenal mucosa and enhanced intestinal cell proliferation, but its effects on gut proteome remain unknown. Therefore, we aimed to assess the effects of an enteral leucine infusion on the whole proteome of duodenal mucosa. In this work, 5 healthy volunteers received for 5h, on 2 occasions and in random order, an enteral supply of maltodextrins (0.25 g kg(-1) h(-1)) or maltodextrins supplemented with leucine (0.035 g kg(-1) h(-1)). At the end of infusion, endoscopic duodenal biopsy samples were collected and analyzed by 2D-PAGE. Eleven protein spots were differentially and significantly (P<0.05) expressed in response to the leucine-supplemented maltodextrins compared with maltodextrins alone. Forty percent of identified proteins by mass spectrometry were located in mitochondria. Four proteins were involved in lipid metabolism: HADHA, ACADVL and CPT2 expressions were reduced, whereas FABP1 expression was increased. In addition, the expression of DHA kinase involved in glycerol metabolism was also downregulated. Finally, leucine supplementation altered the duodenal mucosal proteome by regulating the expression of several enzymes mainly involved in lipid metabolism. These results suggest that leucine supplementation may slowdown fatty acid beta-oxidation in human duodenal mucosa.

Hydrocortisone induces changes in gene expression and differentiation in immature human enterocytes

It is known that functional maturation of the small intestine occurring during the weaning period is facilitated by glucocorticoids (such as hydrocortisone, HC), including an increased expression of digestive hydrolases. However, the molecular mechanisms are not well understood, particularly in the human gut. Here we report a microarray analysis of HC-induced changes in gene expression in H4 cells (a well-characterized human fetal small intestinal epithelial cell line). This study identified a large number of HC-regulated genes, some involved in metabolism, cell cycle regulation, cell-cell or cell-extracellular matrix communication. HC also regulates the expression of genes important for cell maturation such as development of cell polarity, tight junction formation, and interactions with extracellular matrices. Using human small intestinal xenografts, we also show that HC can regulate the expression of genes important for intestinal epithelial cell maturation. Our dataset may serve as a useful resource for understanding and dissecting the molecular mechanisms of intestinal epithelial cell maturation.

Automated pipeline for atlas-based annotation of gene expression patterns: application to postnatal day 7 mouse brain

Massive amounts of image data have been collected and continue to be generated for representing cellular gene expression throughout the mouse brain. Critical to exploiting this key effort of the post-genomic era is the ability to place these data into a common spatial reference that enables rapid interactive queries, analysis, data sharing, and visualization. In this paper, we present a set of automated protocols for generating and annotating gene expression patterns suitable for the establishment of a database. The steps include imaging tissue slices, detecting cellular gene expression levels, spatial registration with an atlas, and textual annotation. Using high-throughput in situ hybridization to generate serial sets of tissues displaying gene expression, this process was applied toward the establishment of a database representing over 200 genes in the postnatal day 7 mouse brain. These data using this protocol are now well-suited for interactive comparisons, analysis, queries, and visualization.

The physiological impact of the serum and glucocorticoid-inducible kinase SGK1

PURPOSE OF REVIEW

The role of serum and glucocorticoid-inducible kinase 1 (SGK1) in renal physiology and pathophysiology is reviewed with particular emphasis on recent advances.

RECENT FINDINGS

The mammalian target of rapamycin complex 2 has been shown to phosphorylate SGK1 at Ser422 (the so-called hydrophobic motif). Ser397 and Ser401 are two additional SGK1-phosphorylation sites required for maximal SGK1 activity. A 5' variant alternate transcript of human Sgk1 has been identified that is widely expressed and shows improved stability, enhanced membrane association, and greater stimulation of epithelial Na+ transport. SGK1 is essential for optimal processing of the epithelial sodium channel and also regulates the expression of the Na+-Cl- cotransporter. With regard to pathophysiology, SGK1 participates in the stimulation of renal tubular glucose transport in diabetes, the renal profibrotic effect of both angiotensin II and aldosterone, and in fetal programing of arterial hypertension.

SUMMARY

The outlined recent findings advanced our understanding of the molecular regulation of SGK1 as well as the role of the kinase in renal physiology and the pathophysiology of renal disease and hypertension. Future studies using pharmacological inhibitors of SGK1 will reveal the utility of the kinase as a new therapeutic target.

Hepatic bile acid metabolism in the neonatal hamster: expansion of the bile acid pool parallels increased Cyp7a1 expression levels

Intraluminal concentrations of bile acids are low in newborn infants and increase rapidly after birth, at least partly owing to increased bile acid synthesis rates. The expansion of the bile acid pool is critical since bile acids are required to stimulate bile flow and absorb lipids, a major component of newborn diets. The purpose of the present studies was to determine the mechanism responsible for the increase in bile acid synthesis rates and the subsequent enlargement of bile acid pool sizes (BAPS) during the neonatal period, and how changes in circulating hormone levels might affect BAPS. In the hamster, pool size was low just after birth and increased modestly until 10.5 days postpartum (dpp). BAPS increased more significantly ( approximately 3-fold) between 10.5 and 15.5 dpp. An increase in mRNA and protein levels of cholesterol 7alpha-hydroxylase (Cyp7a1), the rate-limiting step in classical bile acid synthesis, immediately preceded an increase in BAPS. In contrast, levels of oxysterol 7alpha-hydroxylase (Cyp7b1), a key enzyme in bile acid synthesis by the alternative pathway, were relatively elevated by 1.5 dpp. farnesyl X receptor (FXR) and short heterodimeric partner (SHP) mRNA levels remained relatively constant at a time when Cyp7a1 levels increased. Finally, although simultaneous increases in circulating cortisol and Cyp7a1 levels occurred, precocious expression of Cyp7a1 could not be induced in neonatal hamsters with dexamethasone. Thus the significant increase in Cyp7a1 levels in neonatal hamsters is due to mechanisms independent of the FXR and SHP pathway and cortisol.

A FRET-based assay for characterization of alternative splicing events using peptide nucleic acid fluorescence in situ hybridization

We describe a quantitative method for detecting RNA alternative splicing variants that combines in situ hybridization of fluorescently labeled peptide nucleic acid (PNA) probes with confocal microscopy Förster resonance energy transfer (FRET). The use of PNA probes complementary to sequences flanking a given splice junction allows to specifically quantify, within the cell, the RNA isoform generating such splice junction by FRET measure. As a proof of concept we analyzed two alternative splicing events originating from lymphocyte antigen 6 (LY6) complex, locus G5B (LY6G5B) pre-mRNA. These are characterized by the removal of the first intron (Fully Spliced Isoform, FSI) or by retention of such intron (Intron-Retained Isoform, IRI). The use of PNA probe pairs labeled with donor (Cy3) and acceptor (Cy5) fluorophores, suitable to FRET, flanking FSI and IRI specific splice junctions specifically detected both mRNA isoforms in HeLa cells. We have observed that the method works efficiently with probes 5–11 nt apart. The data supports that this FRET-based PNA fluorescence in situ hybridization (FP–FISH) method offers a conceptually new approach for characterizing at the subcellular level not only splice variant isoform structure, location and dynamics but also potentially a wide variety of close range RNA–RNA interactions.

Steroid and thyroid hormone receptors in mitochondria

Receptors for glucocorticoids, estrogens, androgens, and thyroid hormones have been detected in mitochondria of various cell types by Western blotting, immunofluorescence labeling, confocal microscopy, and immunogold electron microscopy. A role of these receptors in mitochondrial transcription, OXPHOS biosynthesis, and apoptosis is now being revealed. Steroid and thyroid hormones regulate energy production, inducing nuclear and mitochondrial OXPHOS genes by way of cognate receptors. In addition to the action of the nuclearly localized receptors on nuclear OXPHOS gene transcription, a parallel direct action of the mitochondrially localized receptors on mitochondrial transcription has been demonstrated. The coordination of transcription activation in nuclei and mitochondria by the respective receptors is in part realized by their binding to common trans acting elements in the two genomes. Recent evidence points to a role of the mitochondrial receptors in cell survival and apoptosis, exerted by genomic and nongenomic mechanisms. The identification of additional receptors of the superfamily of nuclear receptors and of other nuclear transcription factors in mitochondria increases their arsenal of regulatory molecules and further underlines the central role of these organelles in the integration of growth, metabolic, and cell survival signals.

Intestine-specific ablation of mouse atonal homolog 1 (Math1) reveals a role in cellular homeostasis

BACKGROUND & AIMS

Math1 (Atoh1) is a basic helix-loop-helix transcription factor important for intestinal secretory cell differentiation. We hypothesized that Math1 is important in cell fate commitment, and therefore mediates proliferative homeostasis and the adaptive response following intestinal resection in the adult intestine.

METHODS

We generated mice with an intestine-specific mosaic deletion of Math1 (Math1(Delta intestine)) using the Cre/loxP system. Histologic analysis in adult Math1(Delta intestine) and wild-type littermates at baseline and following small bowel resection or sham surgery was performed.

RESULTS

We observed loss of Paneth, goblet, and enteroendocrine cells in Math1-null crypts. In addition, aberrant activation of the Math1 promoter occurred in absorptive enterocytes derived from Math1-null crypts, suggesting a change in cell fate. Proliferation was increased but apoptosis unchanged in Math1-mutant crypts compared to adjacent wild-type crypts. Math1(Delta intestine) mice and wild-type littermates displayed similar physiologic adaptive responses to small bowel resection as measured by changes in body weight and ileal wet weight. In contrast, Math1-mutant crypts displayed a blunted adaptive response compared to adjacent wild-type crypts.

CONCLUSIONS

We show that Math1 is essential for adult intestinal secretory cell production, and in its absence cells destined to a secretory phenotype instead adopt an absorptive phenotype. Subtle abnormalities of proliferation within Math1-null crypts in Math1(Delta intestine) mice were identified, together with a substantial defect in the adaptive response of Math1-null crypts following small bowel resection. Our results suggest that Math1 is critical for both cell fate determination within the intestinal epithelium and for regulation of the response to intestinal resection.

Gata4 and Hnf1alpha are partially required for the expression of specific intestinal genes during development

The terminal differentiation phases of intestinal development in mice occur during cytodifferentiation and the weaning transition. Lactase-phlorizin hydrolase (LPH), liver fatty acid binding protein (Fabp1), and sucrase-isomaltase (SI) are well-characterized markers of these transitions. With the use of gene inactivation models in mature mouse jejunum, we have previously shown that a member of the zinc finger transcription factor family (Gata4) and hepatocyte nuclear factor-1alpha (Hnf1alpha) are each indispensable for LPH and Fabp1 gene expression but are both dispensable for SI gene expression. In the present study, we used these models to test the hypothesis that Gata4 and Hnf1alpha regulate LPH, Fabp1, and SI gene expression during development, specifically focusing on cytodifferentiation and the weaning transition. Inactivation of Gata4 had no effect on LPH gene expression during either cytodifferentiation or suckling, whereas inactivation of Hnf1alpha resulted in a 50% reduction in LPH gene expression during these same time intervals. Inactivation of Gata4 or Hnf1alpha had a partial effect ( approximately 50% reduction) on Fabp1 gene expression during cytodifferentiation and suckling but no effect on SI gene expression at any time during development. Throughout the suckling period, we found a surprising and dramatic reduction in Gata4 and Hnf1alpha protein in the nuclei of absorptive enterocytes of the jejunum despite high levels of their mRNAs. Finally, we show that neither Gata4 nor Hnf1alpha mediates the glucocorticoid-induced precocious maturation of the intestine but rather are downstream targets of this process. Together, these data demonstrate that specific intestinal genes have differential requirements for Gata4 and Hnf1alpha that are dependent on the developmental time frame in which they are expressed.