Stanniocalcin in terminally differentiated mammalian cells

Low Expression of Stanniocalcin 1 (STC-1) Protein Is Associated With Poor Clinicopathologic Features of Endometrial Cancer

Stanniocalcin-1 (STC-1) is a glycoprotein hormone involved in diverse biological processes, including regulation of calcium phosphate homeostasis, cell proliferation, apoptosis, inflammation, oxidative stress responses, and cancer development. The role of STC-1 in endometrial cancer (EC) is yet to be elucidated. In this study, we investigated the protein expression pattern of STC-1 in a tissue microarray (TMA) cohort of hysterectomy specimens from 832 patients with EC. We then evaluated the prognostic value of STC-1 expression regarding the clinicopathologic features and patients survival over a period of 140 months. Our results revealed that in EC tissue samples, STC-1 is mainly localized in the endometrial epithelium, although some expression was also observed in the stroma. Decreased STC-1 expression was associated with factors relating to a worse prognosis, such as grade 3 endometrioid tumors (p = 0.030), deep myometrial invasion (p = 0.003), lymphovascular space invasion (p = 0.050), and large tumor size (p = 0.001). Moreover, STC-1 expression was decreased in tumors obtained from obese women (p = 0.014) and in women with diabetes mellitus type 2 (DMT2; p = 0.001). Interestingly, the data also showed an association between DNA mismatch repair (MMR) deficiency and weak STC-1 expression, specifically in the endometrial epithelium (p = 0.048). No association was observed between STC-1 expression and disease-specific survival. As STC-1 expression was particularly low in cases with obesity and DMT2 in the TMA cohort, we also evaluated the correlation between metformin use and STC-1 expression in an additional EC cohort that only included women with DMT2 (n = 111). The analysis showed no difference in STC-1 expression in either the epithelium or the stroma in women undergoing metformin therapy compared to metformin non-users. Overall, our data may suggest a favorable role for STC-1 in EC behavior; however, further studies are required to elucidate the detailed mechanism and possible applications to cancer treatment.

STC1 ameliorates cognitive impairment and neuroinflammation of Alzheimer's disease mice via inhibition of ERK1/2 pathway

OBJECTIVE

To investigate the regulatory role of STC1 (Stanniocalcin-1) mediated ERK1/2 pathway in cognitive impairment and neuroinflammation of Alzheimer's disease (AD).

METHODS

WT mice and STC1 Tg mice (transgenic overexpression of STC1) were used to establish AD models to perform behavioral test by Morris water maze. Hippocampal cell apoptosis was quantified by TUNEL staining, the levels of inflammatory cytokines in serum and hippocampal tissues determined by ELISA, as well as oxidative stress-related factors detected by corresponding testing kits, and protein expression of STC1 and ERK1/2 pathway measured by Western blotting.

RESULTS

Compared with WT Sham group, WT AD mice had prolonged escape latency, decreased crossing platform times, increased hippocampal cell apoptosis with up-regulated inflammatory cytokines and oxidative stress-related factors, as well as increased STC1 and ERK1/2 pathway-related molecules. By contrast, STC1 Tg AD mice showed shortened escape latency, increased crossing platform times than WT AD mice, and they also exhibited the decreased apoptosis index and inflammatory cytokines, alleviated oxidative stress-injury, down-regulated protein expression of ERK1/2 pathway, and up-regulated the protein expression of STC1 and UCP2.

CONCLUSION

STC1 overexpression could alleviate oxidative stress-induced injury, reduce neuroinflammation, improve cognitive function to play a neuro-protective role by inhibiting ERK1/2 signaling pathway.

Characterization of stanniocalcin-1 expression in macrophage differentiation

Human stanniocalcin-1 (STC1) is a paracrine factor associated with inflammation and carcinogenesis. The role of STC1 in the pro- and anti-inflammatory functions of differentiating macrophage, however, is not clear. In this study, our data showed that phorbol 12-myristate 13-acetate (PMA) treatment induced human leukemia monocytic cells (ThP-1) differentiation to M0 macrophages. The differentiation was accompanied by a significant increase in the mRNA expression levels of STC1, the pro-inflammatory cytokine TNFα, and anti-inflammatory markers, CD163 & CD206. An intermitted removal of PMA treatment reduced the mRNA levels of STC1 and TNFα but had no noticeable effects on the anti-inflammatory markers. The correlation in the expression of STC1 and pro-inflammatory markers in differentiating macrophages was investigated, using siRNA_STC1-transfected PMA-induced cells. Consistently, the transcripts levels of TNFα and IL-6 were significantly reduced. Moreover, LPS/IFNγ-induced M1-polarization showed remarkably higher expression levels of STC1 than IL-4/IL-13-induced M2-macrophages and PMA-induced M0-macrophages. Transcriptomic analysis of siRNA_STC1-transfected M1-polarized cells revealed an upregulation of TBC1 domain family member 3 (TBC1D3G). The gene regulates the payload of macrophage-released extracellular vesicles to mediate inflammation. The conditioned media from siRNA_STC1-transfected M1-polarized cells were found to reduce Hep3B cell motility. The data suggest that the expression of STC1 were associated with macrophage differentiation, but preferentially to M1 polarization.

Stanniocalcin-1 and -2 effects on glucose and lipid metabolism in white adipose tissue from fed and fasted rats

Stanniocalcin-1 and -2 belong to a family of molecules that exhibit both paracrine and autocrine effects in mammalian cells. Human stanniocalcin-1 (hSTC-1) is expressed in a wide range of tissues, including white adipose tissue. In fed rats, hSTC-1 increases carbon flux from glucose to lipids in retroperitoneal white adipose tissue. Human stanniocalcin-2 (hSTC-2) is expressed in almost all tissues and regulates various biological processes. The aim of this work was to study the action of hSTC-1 and hSTC-2 in the lipid and glucose metabolism of epididymal white adipose tissue (eWAT) in rats in different nutritional states. This study shows for the first time an opposite effect of hSTC-1 and hSTC-2 on glyceride-glycerol generation from glucose in eWAT of fed rats. hSTC-1 stimulated the storage of triacylglycerol in eWAT in the postprandial period, increasing glucose uptake and glyceride-glycerol generation from 14C-glucose. hSTC-2 decreased triacylglycerol synthesis, reducing glyceride-glycerol generation from 14C-glucose, direct phosphorylation of glycerol, and fatty acid synthesis from 14C-glucose in eWAT of fed rats. However, both hormones increased glucose uptake in fed and fasting states. These findings provide evidence for a direct role of hSTC-1 and hSTC-2 in the regulation of lipid and glucose metabolism in eWAT of rats.

Stanniocalcin 1 Enhances Carbon Flux from Glucose to Lipids in White Retroperitoneal Adipose Tissue in the Fed Rat

The present work assesses in vitro the role of human Stanniocalcin 1 (hSTC-1) in glucose metabolism in white retroperitoneal adipose tissue (WRAT) from fed rat. In the fed state, hSTC1 increases the incorporation of ¹⁴C from glucose into lipids in the rat WRAT. The increase in lipogenesis capacity supports the hypothesis that the activity of the glycerol-3-phosphate-generating pathway (glycolysis) from glucose is regulated by hSTC-1. The effect of hSTC-1 on de novo fatty acid synthesis and on glucose oxidation in WRAT is supported by an 85 % increase in ¹⁴CO₂ production from ¹⁴C-glucose. The incubation of WRAT in the presence of hSTC-1 maintained the ADP/ATP ratio close to the control group. The presence of hSTC-1 in the incubation medium did not inhibit the lipolytic effect of epinephrine. In conclusion, hSTC-1 is one of the hormonal factors that control glucose metabolism in WRAT in the fed state.

Stanniocalcin-1 in the subfornical organ inhibits the dipsogenic response to angiotensin II

Recently, receptors for the calcium-regulating glycoprotein hormone stanniocalcin-1 (STC-1) have been found within subfornical organ (SFO), a central structure involved in the regulation of electrolyte and body fluid homeostasis. However, whether SFO neurons produce STC-1 and how STC-1 may function in fluid homeostasis are not known. Two series of experiments were done in Sprague-Dawley rats to investigate whether STC-1 is expressed within SFO and whether it exerts an effect on water intake. In the first series, experiments were done to determine whether STC-1 was expressed within cells in SFO using immunohistochemistry, and whether protein and gene expression for STC-1 existed in SFO using Western blot and quantitative RT-PCR, respectively. Cells containing STC-1 immunoreactivity were found throughout the rostrocaudal extent of SFO. STC-1 protein expression within SFO was confirmed with Western blot, and SFO was also found to express STC-1 mRNA. In the second series, microinjections (200 nl) of STC-1, ANG II, a combination of the two or the vehicle were made into SFO in conscious, unrestrained rats. Water intake was measured at 0700 for a 1-h period after each injection in animals. Microinjections of STC-1 (17.6 or 176 nM) alone had no effect on water intake compared with controls. However, STC-1 not only attenuated the drinking responses to ANG II for about 30 min, but also decreased the total water intake over the 1-h period. These data suggest that STC-1 within the SFO may act in a paracrine/autocrine manner to modulate the neuronal responses to blood-borne ANG II. These findings also provide the first direct evidence of a physiological role for STC-1 in central regulation of body fluid homeostasis.

Neural cell 3D microtissue formation is marked by cytokines' up-regulation

Cells cultured in three dimensional (3D) scaffolds as opposed to traditional two-dimensional (2D) substrates have been considered more physiologically relevant based on their superior ability to emulate the in vivo environment. Combined with stem cell technology, 3D cell cultures can provide a promising alternative for use in cell-based assays or biosensors in non-clinical drug discovery studies. To advance 3D culture technology, a case has been made for identifying and validating three-dimensionality biomarkers. With this goal in mind, we conducted a transcriptomic expression comparison among neural progenitor cells cultured on 2D substrates, 3D porous polystyrene scaffolds, and as 3D neurospheres (in vivo surrogate). Up-regulation of cytokines as a group in 3D and neurospheres was observed. A group of 13 cytokines were commonly up-regulated in cells cultured in polystyrene scaffolds and neurospheres, suggesting potential for any or a combination from this list to serve as three-dimensionality biomarkers. These results are supportive of further cytokine identification and validation studies with cells from non-neural tissue.

Stanniocalcin 1 affects redox status of swine granulosa cells

Stanniocalcin 1 (STC1) is a glycoprotein hormone expressed in different mammalian tissues. In previous studies, we showed STC1 expression in swine ovarian follicles and we demonstrated that STC1 may be a physiological regulator of follicular function. Since reactive oxygen species (ROS) are important signal transducers in the ovary, the present study was undertaken to investigate STC1 action on ROS generation and on the activity of the major enzymatic and non-enzymatic scavengers in swine granulosa cells. O(2)- generation, catalase activity and FRAP levels were increased by STC1, whereas H(2)O(2) generation and peroxidase activity were decreased by STC1. Taken together, our data show that STC1 modulates redox status in swine granulosa cells.

Stanniocalcin, a potential ovarian angiogenesis regulator, does not affect endothelial cell apoptosis

The ovarian follicle represents an outstanding model for the investigation of the angiogenic process. In fact, follicular development is associated with an extensive neovascularization, and physiological angiogenesis is necessary for folliculogenesis. However, although the major factors triggering the angiogenic events have been thoroughly investigated and are now relatively well defined, information about the molecular events involved in the modulation and/or arrest of neovascularization is still scarce. Therefore, this research focused on the potential involvement of stanniocalcin (STC), a protein whose biological function is still unclear, in the control mechanisms of follicular angiogenesis. We evaluated the effect of 5 and 50 ng/mL STC on the production of the main proangiogenic factor, vascular endothelial growth factor (VEGF), by swine granulosa cells. Moreover, STC's effect on cell viability and the modulation of caspase-3 and -7 activities in swine aortic endothelial cells were also examined. Granulosa cell VEGF production was significantly (P < 0.001) inhibited by STC. Endothelial cell viability was significantly (P < 0.001) increased, whereas caspase activities were reduced (P < 0.01) by STC. These data indicate that STC is not angiosuppressive for endothelial cells, although it could potentially modulate local angiogenesis acting at the granulosa cell level.

Expression of stanniocalcin-1 in gastrointestinal tracts of neonatal and mature rats

Stanniocalcin-1 (STC-1) produced by ovaries endocrinologically targets to mammary glands and is secreted into milk during lactation. The decline of mother's serum level by STC-1 antiserum administration reduced the milk fat content and the pups' body fat content. Nevertheless, the pups' fecal fat content was increased, suggesting that milk-derived STC-1 could influence intestinal fat absorption. We investigated the STC-1 expression in rat gastrointestinal tissues using immunocytochemistry and in situ hybridization. STC-1 was widely expressed in the chief cells of gastric pits and the cells of intestinal glands. Goblet cells in the small intestine contained STC-1 protein in their mucus. The distribution shows that this peptide is secreted exocrinologically into the gastrointestinal lumen. Quantitative RT-PCR analysis revealed that the expression ratio was higher in the periods of heavy nutritional demand, such as growing and lactation. The endogenous STC-1, similar to milk-derived STC-1, may be involved in digestion and/or absorption in gastrointestinal organs.

Low-resolution structural studies of human Stanniocalcin-1

BACKGROUND

Stanniocalcins (STCs) represent small glycoprotein hormones, found in all vertebrates, which have been functionally implicated in Calcium homeostasis. However, recent data from mammalian systems indicated that they may be also involved in embryogenesis, tumorigenesis and in the context of the latter especially in angiogenesis. Human STC1 is a 247 amino acids protein with a predicted molecular mass of 27 kDa, but preliminary data suggested its di- or multimerization. The latter in conjunction with alternative splicing and/or post-translational modification gives rise to forms described as STC50 and "big STC", which molecular weights range from 56 to 135 kDa.

RESULTS

In this study we performed a biochemical and structural analysis of STC1 with the aim of obtaining low resolution structural information about the human STC1, since structural information in this protein family is scarce. We expressed STC1 in both E. coli and insect cells using the baculo virus system with a C-terminal 6 x His fusion tag. From the latter we obtained reasonable amounts of soluble protein. Circular dichroism analysis showed STC1 as a well structured protein with 52% of alpha-helical content. Mass spectroscopy analysis of the recombinant protein allowed to assign the five intramolecular disulfide bridges as well as the dimerization Cys202, thereby confirming the conservation of the disulfide pattern previously described for fish STC1. SAXS data also clearly demonstrated that STC1 adopts a dimeric, slightly elongated structure in solution.

CONCLUSION

Our data reveal the first low resolution, structural information for human STC1. Theoretical predictions and circular dichroism spectroscopy both suggested that STC1 has a high content of alpha-helices and SAXS experiments revealed that STC1 is a dimer of slightly elongated shape in solution. The dimerization was confirmed by mass spectrometry as was the highly conserved disulfide pattern, which is identical to that found in fish STC1.

Stanniocalcin-1 suppresses superoxide generation in macrophages through induction of mitochondrial UCP2

Mammalian STC1 decreases the mobility of macrophages and diminishes their response to chemokines. In the current experiments, we sought to determine the impact of STC1 on energy metabolism and superoxide generation in mouse macrophages. STC1 decreases ATP level in macrophages but does not affect the activity of respiratory chain complexes I-IV. STC1 induces the expression of mitochondrial UCP2, diminishing mitochondrial membrane potential and superoxide generation; studies in UCP2 null and gp91phox null macrophages suggest that suppression of superoxide by STC1 is UCP2-dependent yet is gp91phox-independent. Furthermore, STC1 blunts the effects of LPS on superoxide generation in macrophages. Exogenous STC1 is internalized by macrophages within 10 min and localizes to the mitochondria, suggesting a role for circulating and/or tissue-derived STC1 in regulating macrophage function. STC1 induces arrest of the cell cycle at the G1 phase and reduces cell necrosis and apoptosis in serum-starved macrophages. Our data identify STC1 as a key regulator of superoxide generation in macrophages and suggest that STC1 may profoundly affect the immune/inflammatory response.

The murine stanniocalcin 2 gene is a negative regulator of postnatal growth

Stanniocalcin (STC), a secreted glycoprotein, was first studied in fish as a classical hormone with a role in regulating serum calcium levels. There are two closely related proteins in mammals, STC1 and STC2, with functions that are currently unclear. Both proteins are expressed in numerous mammalian tissues rather than being secreted from a specific endocrine gland. No phenotype has been detected yet in Stc1-null mice, and to investigate whether Stc2 could have compensated for the loss of Stc1, we have now generated Stc2(-/-) and Stc1(-/-) Stc2(-/-) mice. Although Stc1 is expressed in the ovary and lactating mouse mammary glands, like the Stc1(-/-) mice, the Stc1(-/-) Stc2(-/-) mice had no detected decrease in fertility, fecundity, or weight gain up until weaning. Serum calcium and phosphate levels were normal in Stc1(-/-) Stc2(-/-) mice, indicating it is unlikely that the mammalian stanniocalcins have a major physiological role in mineral homeostasis. Mice with Stc2 deleted were 10-15% larger and grew at a faster rate than wild-type mice from 4 wk onward, and the Stc1(-/-) Stc2(-/-) mice had a similar growth phenotype. This effect was not mediated through the GH/IGF-I axis. The results are consistent with STC2 being a negative regulator of postnatal growth.

Hypoxic preconditioning induces elevated expression of stanniocalcin-1 in the heart

Animals exposed for a few hours to low oxygen content (8%) develop resistance against further ischemic myocardial damage. The molecular mechanism(s) behind this phenomenon, known as hypoxic preconditioning (HOPC), is still incompletely understood. Stanniocalcin-1 (STC-1) is an evolutionarily conserved glycoprotein originally discovered in fish, in which it regulates calcium/phosphate homeostasis and protects against toxic hypercalcemia. Our group originally reported expression of mammalian STC-1 in brain neurons and showed that STC-1 is a prosurvival factor that guards neurons against hypercalcemic and hypoxic damage. This study investigates the involvement of STC-1 in HOPC-induced cardioprotection. Wild-type mice and IL-6-deficient ( Il-6−/−) mice were kept in hypoxic conditions (8% O2) for 6 h. Myocardial Stc-1 mRNA expression was quantified during hypoxia and after recovery. HOPC triggered a biphasic upregulation of Stc-1 expression in hearts of wild-type mice but not in those of Il-6−/−mice. Treatment of cardiomyocyte cells in culture with hypoxia or IL-6 elicited an Stc-1 response, and ectopically expressed STC-1 in HL-1 cells localized to the mitochondria. Our findings indicate that IL-6-induced expression of STC-1 is one molecular mechanism behind the ischemic tolerance generated by HOPC in the heart.

Hypoxic preconditioning induces neuroprotective stanniocalcin-1 in brain via IL-6 signaling

BACKGROUND AND PURPOSE

Exposure of animals for a few hours to moderate hypoxia confers relative protection against subsequent ischemic brain damage. This phenomenon, known as hypoxic preconditioning, depends on new RNA and protein synthesis, but its molecular mechanisms are poorly understood. Increased expression of IL-6 is evident, particularly in the lungs of animals subjected to hypoxic preconditioning. Stanniocalcin-1 (STC-1) is a 56-kDa homodimeric glycoprotein originally discovered in bony fish, where it regulates calcium/phosphate homeostasis and protects against toxic hypercalcemia. We originally reported expression of mammalian STC-1 in brain neurons and showed that STC-1 guards neurons against hypercalcemic and hypoxic damage.

METHODS

We treated neural Paju cells with IL-6 and measured the induction of STC-1 mRNA. In addition, we quantified the effect of hypoxic preconditioning on Stc-1 mRNA levels in brains of wild-type and IL-6 deficient mice. Furthermore, we monitored the Stc-1 response in brains of wild-type and transgenic mice, overexpressing IL-6 in the astroglia, before and after induced brain injury.

RESULTS

Hypoxic preconditioning induced an upregulated expression of Stc-1 in brains of wild-type but not of IL-6-deficient mice. Induced brain injury elicited a stronger STC-1 response in brains of transgenic mice, with targeted astroglial IL-6 expression, than in brains of wild-type mice. Moreover, IL-6 induced STC-1 expression via MAPK signaling in neural Paju cells.

CONCLUSIONS

These findings indicate that IL-6-mediated expression of STC-1 is one molecular mechanism of hypoxic preconditioning-induced tolerance to brain ischemia.

Neural calcitropic peptides: immunoreactive characterization in fish and invertebrates

Parathyroid hormone (PTH) and stanniocalcin (STC) are primarily produced by the parathyroid glands and corpuscles of Stannius in tetrapods and fish, respectively. However, it is now known that both calcitropic peptides are also synthesized outside of these specialized endocrine glands. The current study employed Western blot analysis to characterize PTH and STC in neural tissues of high- (rats) and low- (hagfish, dogfish, rockfish, trout and skate) vertebrates and invertebrates (starfish, squid, cuttlefish, snails, prawns). Immunoreactive PTH-like peptides, comparable in size to PTH 1-84, were readily detectable in brains of vertebrates lacking (fish) and possessing (rat) parathyroid glands and in invertebrate (snail) ganglia. Immunoreactive STC-like peptides of varying size were similarly detected in brains of vertebrates lacking (rat) and possessing (fish) corpuscles of Stannius and in invertebrate (snail, prawn) ganglia. STC and PTH may thus have evolved as ancestral neuropeptides.