Alternative splicing of the porcine glycogen synthase kinase 3β (GSK-3β) gene with differential expression patterns and regulatory functions

The implications of alternative pre-mRNA splicing in cell signal transduction

Cells produce multiple mRNAs through alternative splicing, which ensures proteome diversity. Because most human genes undergo alternative splicing, key components of signal transduction pathways are no exception. Cells regulate various signal transduction pathways, including those associated with cell proliferation, development, differentiation, migration, and apoptosis. Since proteins produced through alternative splicing can exhibit diverse biological functions, splicing regulatory mechanisms affect all signal transduction pathways. Studies have demonstrated that proteins generated by the selective combination of exons encoding important domains can enhance or attenuate signal transduction and can stably and precisely regulate various signal transduction pathways. However, aberrant splicing regulation via genetic mutation or abnormal expression of splicing factors negatively affects signal transduction pathways and is associated with the onset and progression of various diseases, including cancer. In this review, we describe the effects of alternative splicing regulation on major signal transduction pathways and highlight the significance of alternative splicing.

Glycogen Synthase Kinase 3β (GSK3β) Regulates Myogenic Differentiation in Skeletal Muscle Satellite Cells of Sheep

Glycogen synthase kinase 3β (GSK3β) has a vital role in the regulation of many cellular processes. However, the role of GSK3β in muscle cell differentiation in sheep remains unknown. In this study, we investigated the function of GSK3β in skeletal muscle satellite cells (SMSCs) of sheep. An overexpression of GSK3β significantly inhibited myotube formation as well as the mRNA levels of myogenic genes (MyoD, MyoG, MyHC1, and MyHC2a) in sheep SMSCs. SB216763 treatment had a time-course effect on the phosphorylation levels of sheep GSK3β. In addition, reducing the activity of GSK3β lead to the promotion of sheep SMSCs differentiation as well as the mRNA levels of myogenic genes (MyoD, MyoG, MyHC1, and MyHC2a). This study illustrated the function of GSK3β to inhibit myogenesis in sheep SMSCs, which provided evidence for studying the mechanisms involved in the regulation of sheep SMSCs differentiation by GSK3β.

GSK3: A Kinase Balancing Promotion and Resolution of Inflammation

GSK3 has been implicated for years in the regulation of inflammation and addressed in a plethora of scientific reports using a variety of experimental (disease) models and approaches. However, the specific role of GSK3 in the inflammatory process is still not fully understood and controversially discussed. Following a detailed overview of structure, function, and various regulatory levels, this review focusses on the immunoregulatory functions of GSK3, including the current knowledge obtained from animal models. Its impact on pro-inflammatory cytokine/chemokine profiles, bacterial/viral infections, and the modulation of associated pro-inflammatory transcriptional and signaling pathways is discussed. Moreover, GSK3 contributes to the resolution of inflammation on multiple levels, e.g., via the regulation of pro-resolving mediators, the clearance of apoptotic immune cells, and tissue repair processes. The influence of GSK3 on the development of different forms of stimulation tolerance is also addressed. Collectively, the role of GSK3 as a kinase balancing the initiation/perpetuation and the amelioration/resolution of inflammation is highlighted.

GSK3β inhibition suppresses the hepatic lipid accumulation in Schizothorax prenanti

Glycogen synthase kinase-3β (GSK3β) is a serine/threonine kinase involved in the regulation of embryonic development, glycogen metabolism, protein synthesis, mitosis, and apoptosis. To understand the role of GSK3β in hepatic lipid accumulation of Schizothorax prenanti, we used lithium chloride (LiCl), a GSK3β inhibitor, to inhibit the expression and activity of GSK3β. LiCl increased levels of phosphorylation of GSK3β (Ser9) and decreased the protein level of GSK3β. Plasma TG, TC, and LDL-C levels were greatly decreased after LiCl treatment. Additionally, GSK3β inhibition significantly reduced the levels of hepatic triglyceride (TG) and decreased the expression of lipogenesis-related genes in liver. Interestingly, LiCl decreased levels of phosphorylation of STAT3 (Tyr705), and then inhibited the activity of STAT3. These results indicate that in vivo LiCl treatment, which inhibited GSK3β activity, effectively decreased hepatic lipid accumulation through STAT3 in Schizothorax prenanti.

Astrocytic Insulin-Like Growth Factor-1 Protects Neurons Against Excitotoxicity

Background

Exogenous insulin like growth factor-1 (IGF-1) is known to be neuroprotective in animal models with brain insults, while it can also cause hyperexcitability in rodents. In this regard, the role of endogenous IGF-1 in brain responses to brain insults like excitotoxicity, a common pathology in brain injuries, remains to be elucidated. Here, we investigated the potential role of cell-specific endogenous IGF-1 in the kainic acid (KA) -induced degeneration of the neurons.

Methods

Kainic acid was given to primary cultured cortical neurons and co-cultured astrocytes were added as a supportive system. We evaluated the cell proliferation rate, IGF-1 level in different groups and applied the PCR-Chip assay to explore the downstream of IGF-1. In addition, we applied the viral transfer of astrocytic IGF-1 to rodents treated with KA and assessed the associated molecular marker and behavioral outcomes in these rodents.

Results

We found KA induced increased cell death and hyperphosphorylated tau in neurons; co-cultured astrocytes could prevent these pathologies, and this rescuing effect was abrogated with blockade of the astrocytic IGF-1 with AG1024 (IGF-1R inhibitor). PCR-Chip assay identified that astrocytic IGF-1 could decrease the p-GSK-3 at Tyr 216 in neurons treated with KA and this effect was abrogated with AG1024 as well. In addition, in vivo study showed that gene transfer of astrocytic IGF-1 decreased p-tau and cognitive dysfunction in KA mice.

Conclusion

Our results show astrocytic IGF-1 exhibits neuroprotective properties in neurodegenerative processes in the CNS.

A GYS2/p53 Negative Feedback Loop Restricts Tumor Growth in HBV-Related Hepatocellular Carcinoma

Hepatocellular carcinogenesis is attributed to the reprogramming of cellular metabolism as a consequence of the alteration in metabolite-related gene regulation. Identifying the mechanism of aberrant metabolism is of great potential to provide novel targets for the treatment of hepatocellular carcinoma (HCC). Here, we demonstrated that glycogen synthase 2 (GYS2) restricted tumor growth in hepatitis B virus-related HCC via a negative feedback loop with p53. Expression of GYS2 was significantly downregulated in HCC and correlated with decreased glycogen content and unfavorable patient outcomes. GYS2 overexpression suppressed, whereas GYS2 knockdown facilitated cell proliferation in vitro and tumor growth in vivo via modulating p53 expression. GYS2 competitively bound to MDM2 to prevent p53 from MDM2-mediated ubiquitination and degradation. Furthermore, GYS2 enhanced the p300-induced acetylation of p53 at K373/382, which in turn inhibited the transcription of GYS2 in the support of HBx/HDAC1 complex. In summary, our findings suggest that GYS2 serves as a prognostic factor and functions as a tumor suppressor in HCC. The newly identified HBx/GYS2/p53 axis is responsible for the deregulation of glycogen metabolism and represents a promising therapeutic target for the clinical management of HCC. SIGNIFICANCE: We elucidated the clinical significance, biological function, and regulation of the HBx/GYS2/p53 axis, which supplement the understanding of tumor glycogen metabolism and provide potential prognostic and therapeutic targets for HCC treatment.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/3/534/F1.large.jpg.

GSK3β inhibition attenuates LPS-induced IL-6 expression in porcine adipocytes

IL-6 is not only a proinflammatory cytokine associated with inflammatory responses but also a regulator on the energy and glucose metabolism in adipose tissue. Glycogen synthase kinase 3β (GSK3β) has fundamental roles in the regulation of pro- and anti-inflammatory cytokines production. However, the regulatory role for GSK3β in the pig inflammatory response in adipocytes remains unknown. We show here that SB216763 and LPS increased the phosphorylation of GSK3β (Ser9), and decreased the phosphorylation of GS (Ser641) in adipocytes. The activity of porcine GSK3β was inhibited by SB216763, an inhibitor of GSK3β, attenuated the production of IL-6 in LPS-stimulated adipocytes. Additionally, the essential core region of the pig IL-6 promoter located at -191 bp to -59 bp, and an NF-κBp65 element in this region was responsible for IL-6 promoter activity. The transcription activity of NF-κBp65 was activated by LPS stimulation, and the GSK3β inhibition repressed LPS-induced luciferase activity of the IL-6 promoter. Furthermore, LPS increased p65 binding to the NF-κB site, and GSK3β inhibition had no effect on the association of NF-κBp65 with IL-6 gene promoter after LPS treatment. These results demonstrate that GSK3β has important regulatory roles in the LPS-induced inflammatory response of IL-6 production in pig adipocytes.

Splicing Factor Mutations in Cancer

Many cancers demonstrate aberrant splicing patterns that contribute to their development and progression. Recently, recurrent somatic mutations of genes encoding core subunits of the spliceosome have been identified in several different cancer types. These mutations are most common in hematologic malignancies like the myelodysplastic syndromes (MDS), acute myeloid leukemia, and chronic lymphocytic leukemia, but also in occur in several solid tumors at lower frequency. The most frequent mutations occur in SF3B1, U2AF1, SRSF2, and ZRSR2 and are largely exclusive of each other. Mutations in SF3B1, U2AF1, and SRSF2 acquire heterozygous missense mutations in specific codons, resembling oncogenes. ZRSR2 mutations include clear loss-of-function variants, a pattern more common to tumor suppressor genes. These splicing factors are associated with distinct clinical phenotypes and patterns of mutation in different malignancies. Mutations have both diagnostic and prognostic relevance. Splicing factor mutations appear to affect only a minority of transcripts which show little overlap by mutation type. How differences in splicing caused by somatic mutations of spliceosome subunits lead to oncogenesis is not clear and may involve different targets in each disease type. However, cells with mutated splicing machinery may be particularly vulnerable to further disruption of the spliceosome suggesting a novel strategy for the targeted therapy of cancers.

Transcriptional regulation of pig GYS1 gene by glycogen synthase kinase 3β (GSK3β)

Glycogen synthase kinase 3β (GSK3β) is a ubiquitous serine/threonine kinase and has important roles in glycogen metabolism biosynthesis. Studies have revealed that GSK3β can directly regulate the glycogen synthase activity, yet little is known about the regulation of GSK3β on GYS1 gene transcription. Here, we show that overexpression of GSK3β decreased the mRNA expression level of GYS1. Then we cloned approximately 1.5 kb of pig GYS1 gene promoter region, generated sequential deletion constructs, and evaluated their activity. A gradual increase of the promoter activity was seen with increasing length of the promoter sequence, reaching its highest activity to the sequence corresponding to nt -350 to +224, and then decreased. However, the activities of constructed promoter fragments show different responses to GSK3β co-transfection. By analyzing a series of GYS1 promoter reporter constructs, we have defined two crucial regions (-1488 to -539, -350 to -147) that are responsible for GSK3β-induced transcriptional repression. Furthermore, the ChIP results revealed that only the first and second NF-κB sites of GYS1 promoter could bind to p65, and overexpression of GSK3β induced a significant decrease in p65 binding to the second NF-κB binding site, suggesting that GSK3β may regulate expression of GYS1 gene through binding to the second rather than the first NF-κB site. These data suggest that the NF-κB plays important roles in the transcriptional activity of pig GYS1 gene regulated by GSK3β.

The Role of GSK3β in the Regulation of IL-10 and IL-12 Production Induced by Lipopolysaccharide in PK-15 Cells

Glycogen synthase kinase-3β (GSK3β) plays a fundamental role in the inflammatory response by controlling the balance between pro- and anti-inflammatory cytokine production induced by lipopolysaccharide (LPS). However, the inflammatory roles of different porcine GSK3β isoforms in response to LPS remain unknown. In this study, the activity of porcine GSK3β was inhibited in response to LPS stimulation through increased serine 9 phosphorylation of GSK3β, which increased the production of interleukin (IL)-10 and IL-12 in PK-15 cells. However, treatment with an inhibitor of GSK3β, lithium chloride, significantly increased the production of IL-10 and IL-12 compared with the untreated control and significantly decreased the production of IL-10 and IL-12 compared with LPS stimulation. Moreover, all four glycogen synthase kinase-3 transcripts had positive roles in the production of IL-10 and IL-12 to varying degrees, suggesting their importance in the LPS-induced inflammatory response in pigs.

GSK3β mediates pancreatic cancer cell invasion in vitro via the CXCR4/MMP-2 Pathway

BACKGROUND

Glycogen synthase kinase-3β (GSK3β) expression and activity are upregulated in pancreatic cancer tissues. In our previous study, we found that stromal cell-derived factor-1/ chemokine receptor C-X-C motif chemokine receptor 4 (SDF-1α/CXCR4) upregulated matrix metalloproteinase 2 (MMP-2) and promoted invasion in PANC1 and SW-1990 pancreatic cancer cells by activating p38 mitogen-activated protein kinase (p38 MAPK). Additionally, inhibition of GSK3β reduced MMP-2 secretion.

METHODS

To investigate the molecular mechanism of GSK3β in pancreatic cancer tissues, we created stable PANC1 cells up-regulation of GSK3β by transfecting GSK3β overexpression plasmid, and down-regulation of GSK3β using two different types of RNA interference.

RESULTS

Western blotting showed that overexpression of GSK3β up-regulated CXCR4 and MMP-2 expression; suppression of GSK3β down-regulated CXCR4 and MMP-2 protein expression. Up-regulation of MMP2 induced by overexpression of GSK3β was blocked by inhibition of CXCR4. Overexpression of GSK3β promoted PANC1 cell invasion, and down-regulation of GSK3β suppressed PANC1 cell invasion in the transwell invasion assays. However, inhibition of CXCR4 using shRNA attenuated the ability of GSK3β to promote PANC1 cell invasion.

CONCLUSIONS

This study demonstrated that GSK3β promotes PANC1 cell invasion via the CXCR4/MMP-2 pathway.

Multiple alternative splicing and differential expression pattern of the glycogen synthase kinase-3β (GSK3β) gene in goat (Capra hircus)

Glycogen synthase kinase-3β (GSK3β) has been identified as a key protein kinase involved in several signaling pathways, such as Wnt, IGF-Ι and Hedgehog. However, knowledge regarding GSK3β in the goat is limited. In this study, we cloned and characterized the goat GSK3β gene. Six novel GSK3β transcripts were identified in different tissues and designated as GSK3β1, 2, 3, 4, 5 and 6. RT-PCR was used to further determine whether the six GSK3β transcripts existed in different goat tissues. Bioinformatics analysis revealed that the catalytic domain (S_TKc domain) is missing from GSK3β2 and GSK3β4. GSK3β3 and GSK3β6 do not contain the negative regulatory sites that are controlled by p38 MAPK. Furthermore, qRT-PCR and western blot analysis revealed that all the GSK3β transcripts were expressed at the highest level in the heart, whereas their expression levels in the liver, spleen, kidney, brain, longissimus dorsi muscle and uterus were different. These studies provide useful information for further research on the functions of GSK3β isoforms.

Identification of porcine glycogen synthase kinase 3α (GSK-3α) gene and its association with carcass traits

GSK-3 plays an important role on numerous cellular processes involved in the regulation of embryonic development, protein synthesis, glycogen metabolism, inflammatory, mitosis and apoptosis. In this study, we obtained the cDNA and promoter sequences of the porcine GSK-3α gene, analyzed its genomic organization and mapped it to SSC6q12 through comparative mapping method. Moreover, the qRT-PCR analysis revealed that porcine GSK-3α gene was widely expressed in many tissues, and a high expression level was observed in the brain and spleen. In addition, seven single-nucleotide polymorphisms were detected in the promoter region of porcine GSK-3α gene. Association analysis revealed that the GSK-3α Hin1I and MspI polymorphisms both had significant associations (p < 0.05) with loin muscle area, average backfat thickness, thorax-waist fat thickness, and buttock fat thickness. These results provide useful information for further investigation on the function of porcine GSK-3α gene.