Expression analysis of RSK gene family members: the RSK2 gene, mutated in Coffin-Lowry syndrome, is prominently expressed in brain structures essential for cognitive function and learning.
Coffin-Lowry syndrome (CLS) is characterized by cognitive impairment, characteristic facial and digital findings and skeletal anomalies. The gene implicated in CLS encodes RSK2, a serine/threonine kinase acting in the Ras/MAPK signalling pathway. In humans, RSK2 belongs to a family of four highly homologous proteins (RSK1-RSK4), encoded by distinct genes. RSK2 mutations in CLS patients are extremely heterogeneous. No consistent relationship between specific mutations and the severity of the disease or the expression of uncommon features has been established. Together, the data suggest an influence of environmental and/or other genetic components on the presentation of the disease. Obvious modifying genes include those encoding other RSK family members. In this study we have determined the expression of RSK1, 2 and 3 genes in various human tissues, during mouse embryogenesis and in mouse brain. The three RSK mRNAs were expressed in all human tissues and brain regions tested, supporting functional redundancy. However, tissue specific variations in levels suggest that they may also serve specific roles. The mouse Rsk3 gene was prominently expressed in the developing neural and sensory tissues, whereas Rsk1 gene expression was the strongest in various other tissues with high proliferative activity, suggesting distinct roles during development. In adult mouse brain, the highest levels of Rsk2 expression were observed in regions with high synaptic activity, including the neocortex, the hippocampus and Purkinje cells. These structures are essential components in cognitive function and learning. Based on the expression levels, our results suggest that in these areas, the Rsk1 and Rsk3 genes may not be able to fully compensate for a lack of Rsk2 function. (+info)
Coffin-Lowry syndrome: odontologic characteristics. Review of the literature and presentation of a clinical case.
A description is made of the general and odontologic characteristics of Coffin-Lowry syndrome, with a review of the literature and the report of a clinical case. (+info)
Ataxia telangiectasia mutated proteins, MAPKs, and RSK2 are involved in the phosphorylation of STAT3.
Phosphorylation at Ser(727) is known to be required for complete activation of STAT3 by diverse stimuli including UV irradiation, but the kinase(s) responsible for phosphorylating STAT3 (Ser(727)) is still not well discerned. In the present study, we observed that activation of ATM is required for a UVA-stimulated increase in Ser(727) phosphorylation of STAT3 as well as in activation and phosphorylation of p90 ribosomal protein S6 kinases (RSKs). Moreover, UVA-stimulated activation of upstream kinases, such as c-Jun N-terminal kinases (JNKs) and ERKs, involved in mediating phosphorylation of RSKs and STAT3 was defective or delayed in ATM-deficient cells. Furthermore, we provide evidence that RSK2-deficient cells were defective for UV-induced Ser(727) phosphorylation of STAT3, and the defect was restored after ectopic expression of transfected full-length RSK2. In vitro experiments showed that active RSK2 and JNK1 induce the phosphorylation of STAT3 precipitates from immunoprecipitation but not from glutathione S-transferase (GST) pull-down. Interestingly, the GST fusion STAT3 proteins mixed together with STAT3 immunoprecipitates can be phosphorylated by JNK. However, the in vitro phosphorylation of STAT3 was reduced by the GST-STAT3 beta protein, a dominant negative form of STAT3. Taken together, our results demonstrate that the STAT3 phosphorylation at Ser(727) is triggered by active RSK2 or JNK1 in the presence of a downstream kinase or a cofactor, and thereby the intracellular phosphorylation process is stimulated through a signaling pathway involving ATM, MAPKs, RSK2, and an as yet unidentified kinase or cofactor. Additionally, RSK2-mediated phosphorylation of STAT3 (Ser(727)) was further determined to be required for basal and UVA-stimulated STAT3 transcriptional activities. (+info)
Delineation of the mechanisms of aberrant splicing caused by two unusual intronic mutations in the RSK2 gene involved in Coffin-Lowry syndrome.
Coffin-Lowry syndrome (CLS) is caused by mutations in the RSK2 gene encoding a protein kinase of the Ras signalling pathway. We have studied two point mutations which cause aberrant splicing but do not concern the invariant GT or AG nucleotides of splice sites. The first, an A-->G transition at position +3 of the 5' splice site of exon 6, results in vivo and in vitro in exon skipping and premature translation termination. The natural 5' splice site, although intrinsically weak, is not transactivated under normal conditions. Consequently, replacement of an A/U by a G/U base pairing with U1 snRNA reduces its strength below a critical threshold. The second mutation, an A-->G transition 11 nt upstream of exon 5, creates a new AG near the natural 3' splice site. In vitro this synthetic 3' AG is used exclusively by the splicing machinery. In vivo this splicing event is also observed, but is underestimated because the resulting RSK2 mRNA contains premature stop codons which trigger the nonsense-mediated decay process. We show that a particular mechanism is involved in the aberrant splicing of exon 5, implying involvement of the natural 3' AG during the first catalytic step and the new 3' AG during the second step. Thus, our results explain how these mutations cause severe forms of CLS. (+info)
Essential role of RSK2 in c-Fos-dependent osteosarcoma development.
Inactivation of the growth factor-regulated S6 kinase RSK2 causes Coffin-Lowry syndrome in humans, an X-linked mental retardation condition associated with progressive skeletal abnormalities. Here we show that mice lacking RSK2 develop a progressive skeletal disease, osteopenia due to impaired osteoblast function and normal osteoclast differentiation. The phenotype is associated with decreased expression of Phex, an endopeptidase regulating bone mineralization. This defect is probably not mediated by RSK2-dependent phosphorylation of c-Fos on serine 362 in the C-terminus. However, in the absence of RSK2, c-Fos-dependent osteosarcoma formation is impaired. The lack of c-Fos phosphorylation leads to reduced c-Fos protein levels, which are thought to be responsible for decreased proliferation and increased apoptosis of transformed osteoblasts. Therefore, RSK2-dependent stabilization of c-Fos is essential for osteosarcoma formation in mice and may also be important for human osteosarcomas. (+info)
p90 ribosomal S6 kinase 2 exerts a tonic brake on G protein-coupled receptor signaling.
G protein-coupled receptors (GPCRs) are essential for normal central CNS function and represent the proximal site(s) of action for most neurotransmitters and many therapeutic drugs, including typical and atypical antipsychotic drugs. Similarly, protein kinases mediate many of the downstream actions for both ionotropic and metabotropic receptors. We report here that genetic deletion of p90 ribosomal S6 kinase 2 (RSK2) potentiates GPCR signaling. Initial studies of 5-hydroxytryptamine (5-HT)(2A) receptor signaling in fibroblasts obtained from RSK2 wild-type (+/+) and knockout (-/-) mice showed that 5-HT(2A) receptor-mediated phosphoinositide hydrolysis and both basal and 5-HT-stimulated extracellular signal-regulated kinase 1/2 phosphorylation are augmented in RSK2 knockout fibroblasts. Endogenous signaling by other GPCRs, including P2Y-purinergic, PAR-1-thrombinergic, beta1-adrenergic, and bradykinin-B receptors, was also potentiated in RSK2-deficient fibroblasts. Importantly, reintroduction of RSK2 into RSK2-/- fibroblasts normalized signaling, thus demonstrating that RSK2 apparently modulates GPCR signaling by exerting a "tonic brake" on GPCR signal transduction. Our results imply the existence of a novel pathway regulating GPCR signaling, modulated by downstream members of the extracellular signal-related kinase/mitogen-activated protein kinase cascade. The loss of RSK2 activity in humans leads to Coffin-Lowry syndrome, which is manifested by mental retardation, growth deficits, skeletal deformations, and psychosis. Because RSK2-inactivating mutations in humans lead to Coffin-Lowry syndrome, our results imply that alterations in GPCR signaling may account for some of its clinical manifestations. (+info)
Mutations in the RSK2(RPS6KA3) gene cause Coffin-Lowry syndrome and nonsyndromic X-linked mental retardation.
We describe three families with X-linked mental retardation, two with a deletion of a single amino acid and one with a missense mutation in the proximal domain of the RSK2(RPS6KA3) (ribosomal protein S6 kinase, 90 kDa, polypeptide 3) protein similar to mutations found in Coffin-Lowry syndrome (CLS). In two families, the clinical diagnosis had been nonsyndromic X-linked mental retardation. In the third family, although CLS had been suspected, the clinical features were atypical and the degree of intellectual disability much less than expected. These families show that strict reliance on classical clinical criteria for mutation testing may result in a missed diagnosis. A less targeted screening approach to mutation testing is advocated. (+info)
Protein nutrition as therapy for a genetic disorder of bone?
Bone formation is controlled by a network of transcription factors and signaling molecules. In this issue, , studying the role of the transcription factor ATF4 in a new mouse model of neurofibromatosis type I skeletal defects, demonstrate striking effects of changing dietary protein on bone formation abnormalities. (+info)