RSK2, also known as RPS6KA3 (ribosomal protein S6 kinase, 90 kDa, polypeptide 3), is a downstream kinase of the mitogen-activated protein kinase (MAPK) pathway, which is important in regulating survival, transcription, growth and proliferation. However, its biological role in mitotic progression is not well understood. In this study, we examined the potential involvement of RSK2 in the regulation of mitotic progression. Interestingly, depletion of RSK2, but not RSK1, caused the accumulation of mitotic cells. Time-lapse analysis revealed that mitotic duration, particularly the duration for metaphase-to-anaphase transition was prolonged in RSK2-depleted cells, suggesting activation of spindle assembly checkpoint (SAC). Indeed, more BubR1 (Bub1-related kinase) was present on metaphase plate kinetochores in RSK2-depleted cells, and depletion of BubR1 abolished the mitotic accumulation caused by RSK2 depletion, confirming BubR1-dependent SAC activation. Along with the shortening of inter-kinetochore distance, these data suggested that weakening of the tension across sister kinetochores by RSK2 depletion led to the activation of SAC. To test this, we analyzed the RSK2 effects on the stability of kinetochore–microtubule interactions, and found that RSK2-depleted cells formed less kinetochore–microtubule fibers. Moreover, RSK2 depletion resulted in the decrease of basal level of microtubule as well as an irregular distribution of mitotic spindles, which might lead to observed several mitotic progression defects such as increase in unaligned chromosomes, defects in chromosome congression and a decrease in pole-to-pole distance in these cells. Taken together, our data reveal that RSK2 affects mitotic progression by regulating the distribution, basal level and the stability of mitotic spindles.
Humans ; Kinetochores ; M Phase Cell Cycle Checkpoints ; Metaphase ; Microtubules ; Phosphotransferases ; Protein Kinases ; Ribosomal Protein S6 Kinases ; Ribosomal Protein S6 Kinases, 90-kDa* ; Siblings ; Spindle Apparatus*

OBJECTIVE: To identify potential mutations of the CLS gene in a Chinese pedigree affected with Coffin-Lowry syndrome. METHODS: Whole exome sequencing was applied to detect potential mutation in the proband, and the result was verified by Sanger sequencing. RESULTS: The proband was found to carry a c.966_967delAA (p.Arg323Thr fs*11) deletional mutation in the RPS6KA3 gene. The same mutation was also found in his mother. CONCLUSION The c.966_967delAA (p.Arg323Thr fs*11) deletional mutation of the RPS6KA3 gene probably underlies the disorder in this pedigree.
Asian Continental Ancestry Group ; China ; Coffin-Lowry Syndrome ; genetics ; Humans ; Mutation ; Pedigree ; Ribosomal Protein S6 Kinases, 90-kDa ; genetics ; Sequence Deletion

OBJECTIVEIn order to provide theoretic evidence of exercise preventing insulin resistance, we studied the effects of high-fat diet and aerobic exercise on expression of mammalian target of rapamycin/ribosomal protein kinase (mTOR/S6K1) in skeletal muscle of insulin resistant mice.

METHODS8-week old, C57BL/6 mice were divided into two groups: which are normal chow and high-fat diet groups, each group has 20 animals feeding by normal chow and high fat diet respectively. 8-weeks later, mice from high fat diet group were proved to have insulin resistance symptoms and after that time point the mice were regrouped. The normal chow group was randomly divided into normal chow diet control group (NC) and normal chow exercise group (NE), and the high fat diet group was randomly divided into high fat diet control group (HC) and high fat diet exercise group (HE). All exercise groups were required to running on treadmill for 6 weeks. Mice were acclimatized to the motorized treadmill by running 60 min per day at the intensity of 75% VO2max five days per week for 6 weeks. By the end of training, we observed the changes of glucose tolerance by oral glucose tolerance test and morphology of pancreatic islet under microscope. Insulin concentration was measured by ELISA. Northern blot and Western blot were performed to detect mTOR, S6K1 (and/or pS6K1-Thr389) mRNA and protein expression in skeletal muscle.

RESULTSBy comparing with NC group, the effect of high-fat diet increased the body weight, fasting serum insulin level and the area of pancreatic islet of the mice in HC group significantly. Furthermore, glucose tolerance was impaired. After 6-week aerobic exercise, above value of descriptive index were significantly decreased in skeletal muscle in HE group. In addition, OGTT was also improved. The expression of mTOR, S6K1 (and/or pS6K1-Thr389) mRNA and protein were significantly decreased.

CONCLUSIONmTOR/S6K1 signaling pathway plays an important role in the development of diet induced insulin resistance. Aerobic exercise attenuates insulin resistance by increasing skeletal muscle insulin sensitivity evidenced by increased energy metabolism decreased activity of mTOR/S6K1 signaling pathway.

Animals ; Body Weight ; Diet, High-Fat ; Glucose Tolerance Test ; Insulin ; blood ; Insulin Resistance ; Male ; Mice ; Mice, Inbred C57BL ; Muscle, Skeletal ; metabolism ; Physical Conditioning, Animal ; physiology ; Ribosomal Protein S6 Kinases, 90-kDa ; metabolism ; Signal Transduction ; TOR Serine-Threonine Kinases ; metabolism

Liver cancer occurs very frequently worldwide and hepatocellular carcinoma (HCC) accounts for more than 80% of total primary liver cancer cases. In this study, the anticarcinogenic effects of resveratrol against hepatitis B virus (HBV)-induced HCC were investigated by using HBV X-protein-overexpressing Huh7 (Huh7-HBx) human hepatoma cells. MTT assay showed that resveratrol decreased cell viability. Fluorescence-activated cell-sorter analysis showed that resveratrol induced G1 cell cycle arrest without increasing the sub-G1 phase cell population. Therefore, we evaluated its effect on regulation of cyclin D1, which is critically involved in G1/S transition. Resveratrol lowered cyclin D1 transcription. Western blot analysis of the effects of resveratrol on upstream cyclin D1 transcriptional signaling, extracellular signal-related kinase (ERK), p90(RSK), Akt, and p70(S6K) revealed inhibition of Akt but not the ERK signaling pathway. Collectively, the results indicate that resveratrol inhibits Huh7-HBx proliferation by decreasing cyclin D1 expression through blockade of Akt signaling. We investigated the anticarcinogenic effect and mechanism of resveratrol in xenograft model mice implanted with Huh7-HBx cells. Intraperitoneal resveratrol injection reduced tumor size in the mice. Expression of survivin was reduced, but cyclin D1 was not affected. The results demonstrate that resveratrol treatment may help manage HBV-induced HCC by regulating survivin.
Animals ; Anticarcinogenic Agents ; Blotting, Western ; Carcinoma, Hepatocellular* ; Cell Survival ; Cyclin D1 ; G1 Phase Cell Cycle Checkpoints ; Hepatitis B virus* ; Hepatitis B* ; Hepatitis* ; Heterografts ; Humans ; Liver Neoplasms ; Mice ; Phosphotransferases ; Ribosomal Protein S6 Kinases, 90-kDa

p90 ribosomal S6 kinase (p90RSK), one of the downstream effectors in ERK1/2 pathways, shows high expression in human breast cancer tissues. However, its role in breast cancer development and drug resistance is not fully understood. Here, we demonstrate that Cis-DDP treatment failed to increase cytotoxicity in MDA-MB-231 cells compared to MCF-7 cells and p90RSK activation was involved in Cis-DDP-resistance to MDA-MB-231 cells. In the study, we found that inhibition of p90RSK expression or activation using a small interfering RNA (siRNA) or dominant-negative kinase mutant (DN-p90RSK) plasmid overexpression increased Cis-DDP-induced cytotoxicity of MDA-MB-231 cells, respectively. Mechanistically, we found that Cis-DDP resistance was associated with up-regulation of epithelial growth factor (EGF) expression and EGF treatment induced cancer survival signaling pathway including activation of ERK1/2, p90RSK, and Akt. We also examined the expression of epithelial-mesenchymal transition (EMT)-associated proteins using a reverse transition-quantitative PCR analysis. Cis-DDP treatment induced EMT by increasing the expression levels of N-cadherin, Snail, and Twist, while decreasing the expression levels of E-cadherin. Furthermore, we examined the epithelial marker, Zonula occludens-1 (ZO-1) using immunofluorescence analysis and found that Cis-DDP-inhibited ZO-1 expression was recovered by p90RSK deactivated condition. Therefore, we conclude that Cis-DDP resistance is involved in EMT via regulating the EGF-mediated p90RSK signaling pathway in MDA-MB-231 cells.
Breast Neoplasms ; Cadherins ; Cisplatin ; Drug Resistance ; Epidermal Growth Factor ; Epithelial-Mesenchymal Transition ; Fluorescent Antibody Technique ; Humans ; MCF-7 Cells ; Phosphotransferases ; Plasmids ; Polymerase Chain Reaction ; Ribosomal Protein S6 Kinases, 90-kDa ; RNA, Small Interfering ; Snails ; Triple Negative Breast Neoplasms ; Up-Regulation

OBJECTIVETo study the role of S6K1 in the induction of SREBP1c in mouse hepatic cell by high glucose stimulation.

METHODSS6K1 shRNA recombinant adenovirus (S6K1Ax) was injected into tail vein of db/db mice and then hepatic triglycerol content was analyzed. Liver specimen were stained with HE. After transfection with S6K1Ax or pU6Ax, mouse hepatic AML12 cells were treated with high glucose, insulin or glucose and insulin, the expression of mSREBP1c was detected by RT-PCR. S6K1 protein was detected by Western blot.

RESULTSHepatic S6K1 protein in db/db mice was inhibited a week after S6K1Ax injection. Compared with the control group, hepatic triglycerol content of S6K1Ax group was decreased (0.65+/-0.02) mmol/L vs (0.56+/-0.01) mmol/L (t = 4.312, P less than 0.01), hepatocyte fat droplet and vaculor generation were also decreased, fatty liver was improved. The mSREBP1c expression in S6K1Ax transfected cells was lower than that in the control cells (0.03+/-0.01 vs 0.06+/-0.01, t = 5.624, P less than 0.01). Compared with the basal state, SREBP1c expression of both groups was increased on the insulin stimulation, S6K1Ax group was 0.06+/-0.02 (t = 8.452, P less than 0.01) and control group was 0.08+/-0.02 (t = 3.591, P less than 0.05). There is no difference between control and S6K1Ax group by glucose addition (P more than 0.05).

CONCLUSIONS6K1 acts on fatty synthesis by regulating mSREBP1c expression.

Adenoviridae ; genetics ; Animals ; Cell Line ; Fatty Acid Synthases ; genetics ; metabolism ; Gene Expression Regulation ; Glucose ; administration & dosage ; Insulin ; administration & dosage ; Liver ; metabolism ; pathology ; Liver Cirrhosis ; etiology ; metabolism ; pathology ; Mice ; Mice, Inbred Strains ; RNA Interference ; RNA, Messenger ; genetics ; metabolism ; Reverse Transcriptase Polymerase Chain Reaction ; Ribosomal Protein S6 Kinases, 90-kDa ; genetics ; metabolism ; Staining and Labeling ; Sterol Regulatory Element Binding Protein 1 ; genetics ; metabolism ; Transfection ; Triglycerides ; metabolism

OBJECTIVETo study the expression and clinical significance of ribosomal S6 kinase-4 (RSK-4) in breast cancer and explore the role of RSK-4 in the genesis and development of breast cancer.

METHODThe expression levels of RSK-4 mRNA and protein were detected in 56 cases of breast cancer and the normal breast tissues, as well as in 20 cases of breast benign lesions, by reverse transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry.

RESULTSThe expression rates of RSK-4 mRNA in breast cancer, the normal breast tissues and breast benign lesions were 48.2%, 76.8% and 75.0%, respectively. The expression level of RSK-4 mRNA in breast cancer was significantly lower than those in normal breast tissues and breast benign lesions tissues (P < 0.05). The expression level of RSK-4 significantly correlated with tumor size and clinical stage (P < 0.05).The expression rate of RSK-4 protein was 39.3% in breast cancer tissues, which was significantly lower than that of normal breast tissues (71.4%) and breast benign lesions (75.0%, P < 0.01). The expression level of RSK-4 protein was lower in breast cancer with large tumor, high clinical stage and lymph node metastasis. In 56 cases of breast cancer samples, the consistency rate of RSK-4 mRNA and protein was 73.2%. A significant correlation was found between RSK-4 mRNA and protein (χ² = 10.254, P < 0.05).

CONCLUSIONThe down-regulation of RSK-4 expression in breast caner suggests that it is a breast cancer suppressor gene, and the lack or down-regulation of RSK-4 expression is involved in the genesis and progression of breast cancer.

Adult ; Aged ; Breast ; metabolism ; Breast Neoplasms ; metabolism ; pathology ; Carcinoma, Ductal, Breast ; metabolism ; pathology ; Down-Regulation ; Female ; Fibroadenoma ; metabolism ; pathology ; Humans ; Lymphatic Metastasis ; Middle Aged ; Neoplasm Staging ; RNA, Messenger ; metabolism ; Ribosomal Protein S6 Kinases, 90-kDa ; genetics ; metabolism ; Tumor Burden ; Young Adult

Mouse double minute 2 (Mdm2) gene was isolated from a cDNA library derived from transformed mouse 3T3 cells, and was classified as an oncogene as it confers 3T3 and Rat2 cells tumorigenicity when overexpressed. It encodes a nucleocytoplasmic shuttling ubiquitin E3 ligase, with its main target being tumor suppressor p53, which is mutated in more than 50% of human primary tumors. Mdm2's oncogenic activity is mainly mediated by p53, which is activated by various stresses, especially genotoxic stress, via Atm (ataxia telangiectasia mutated) and Atr (Atm and Rad3-related). Activated p53 inhibits cell proliferation, induces apoptosis or senescence, and maintains genome integrity. Mdm2 is also a target gene of p53 transcription factor. Thus, Mdm2 and p53 form a feedback regulatory loop. External and internal cues, through multiple signaling pathways, can act on Mdm2 to regulate p53 levels and cell proliferation, death, and senescence. This review will focus on how Mdm2 is regulated under genotoxic stress, and by the Akt1-mTOR-S6K1 pathway that is activated by insulin, growth factors, amino acids, or energy status.
3T3 Cells ; Animals ; Apoptosis ; Cell Proliferation ; Cellular Senescence ; DNA Damage ; Energy Metabolism ; Feedback, Physiological ; Gene Library ; Humans ; Intercellular Signaling Peptides and Proteins ; metabolism ; Mice ; Molecular Targeted Therapy ; Mutation ; Neoplasms ; genetics ; metabolism ; Proto-Oncogene Proteins c-mdm2 ; genetics ; metabolism ; Ribosomal Protein S6 Kinases, 90-kDa ; genetics ; metabolism ; Signal Transduction ; genetics ; TOR Serine-Threonine Kinases ; genetics ; metabolism ; Tumor Suppressor Protein p53 ; genetics ; metabolism ; Ubiquitin-Protein Ligases ; genetics ; metabolism