Functional Characterization of Human RSK4, a New 90-kDa Ribosomal S6 Kinase, Reveals Constitutive Activation in Most Cell Types

Dümmler, Bettina; Hauge, Camilla; Silber, Joachim; Yntema, Helger G.; Kruse, Lars Schack; Kofoed, Birte; Hemmings, Brian A.; Alessi, Dario R.; Frödin, Morten

doi:10.1074/jbc.m408194200

Cited by 101 publications

(97 citation statements)

References 55 publications

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“…A higher expression of these two putative tumor suppressor genes in breast cancer biopsy samples compared with adjacent normal mammary tissues conflicts with previous in vitro studies that suggest that these two genes have growth inhibitory activity (19)(20)(21)(22)(23). However, this is the first study to screen the mRNA and protein expression of these two genes (RbAp46 and Rsk4) and other putative tumor suppressor gene (Cldn2) in human breast cancer and adjacent normal tissues.…”

Section: Discussioncontrasting

confidence: 51%

“…Surprisingly, we found that a large percentage of breast cancer cases had high expression of two putative tumor suppressor genes (Rsk4 and RbAp46), which have been shown to be growth inhibitory genes in in vitro studies (19)(20)(21)(22)(23). The RbAp46 gene showed increased expression in 79% of cases (15 of 19) compared with adjacent mammary tissues.…”

Section: Expression Of Tumor Suppressor Genes and Oncogenes Mrna In Hmentioning

confidence: 99%

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Aberrant Expression of X-Linked Genes RbAp46, Rsk4, and Cldn2 in Breast Cancer

Thakur

Rahman

et al. 2007

Molecular Cancer Research

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The consequence of activation status or gain/loss of an X-chromosome in terms of the expression of tumor suppressor genes or oncogenes in breast cancer has not been clearly addressed. In this study, we investigated the activation status of the X-chromosomes in a panel of human breast cancer cell lines, human breast carcinoma, and adjacent mammary tissues and a panel of murine mammary epithelial sublines ranging from low to high invasive potentials. Results show that most human breast cancer cell lines were homozygous, but both benign cell lines were heterozygous for highly polymorphic X-loci (IDS and G6PD). On the other hand, 60% of human breast carcinoma cases were heterozygous for either IDS or G6PD markers. Investigation of the activation status of heterozygous cell lines revealed the presence of only one active X-chromosome, whereas most heterozygous human breast carcinoma cases had two active X-chromosomes. Furthermore, we determined whether or not an additional active X-chromosome affects expression levels of tumor suppressor genes and oncogenes. Reverse transcription-PCR data show high expression of putative tumor suppressor genes Rsk4 and RbAp46 in 47% and 79% of breast carcinoma cases, respectively, whereas Cldn2 was down-regulated in 52% of breast cancer cases compared with normal adjacent tissues. Consistent with mRNA expression, immunostaining for these proteins also showed a similar pattern. In conclusion, our data suggest that high expression of RbAp46 is likely to have a role in the development or progression of human breast cancer. The activation status of the X-chromosome may influence the expression levels of X-linked oncogenes or tumor suppressor genes. (Mol Cancer Res 2007;5(2):171 -81)

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Section: Discussioncontrasting

confidence: 51%

Section: Expression Of Tumor Suppressor Genes and Oncogenes Mrna In Hmentioning

confidence: 99%

Aberrant Expression of X-Linked Genes RbAp46, Rsk4, and Cldn2 in Breast Cancer

Thakur

Rahman

et al. 2007

Molecular Cancer Research

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“…Initially, RPS6KA1 (p90 Rsk-1) and RPS6KA3 (p90 Rsk-2) were identified (Frodin and Gammeltoft, 1999). Subsequently, RPS6KA2 (p90 Rsk-3) was isolated and more recently, RPS6KA6 (p90 Rsk-4) (Moller et al, 1994;Zhao et al, 1995;Yntema et al, 1999;Dummler et al, 2005). RPS6KA4 (Msk-1) and RPS6KA5 (Msk-2) are less homologous to the first four members of the RSK family.…”

Section: Discussionmentioning

confidence: 99%

“…pMT2 plasmids expressing RPS6KA1 (RSK1) and RPS6KA3 (RSK2) were obtained from Dr M Greenberg (Xing et al, 1998); RPS6KA2 (RSK3) and K91A-RPS6KA2 (K91A-RSK3) from Dr C Bjorbaek ; and RPS6KA6 (RSK4) was obtained from Dr M Fro¨din (Dummler et al, 2005). Full-length cDNA of RPS6KA genes were released from the pMT2 vector using EcoRI digestion and subcloned with or without a HA tag (as a linker with overhangs for restriction sites KpnI and BamHI, (CATG-TACCCATAC-GATGTTCCAGATTACGCTGGG) into the eukaryotic expression vectors, pcDNA3/neo, pcDNA3.1, pcDNA4/TO and pcDNA5/TO (Invitrogen, Paisley, Strathclyde, UK), and pEGFP-C3 (BD Biosciences).…”

Section: Methodsmentioning

confidence: 99%

RPS6KA2, a putative tumour suppressor gene at 6q27 in sporadic epithelial ovarian cancer

et al. 2006

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We had previously defined by allele loss studies a minimal region at 6q27 (between D6S264 and D6S297) to contain a putative tumour suppressor gene. The p90 ribosomal S6 kinase-3 gene (p90 Rsk-3, RPS6KA2) maps in this interval. It is a serine-threonine kinase that signals downstream of the mitogen-activated protein kinase pathway. It is expressed in normal ovarian epithelium, whereas reduced or absent in tumours or cell lines. We show that RPS6KA2 is monoallelically expressed in the ovary suggesting that loss of a single expressed allele is sufficient to cause complete loss of expression in cancer cells. Further, we have identified two new isoforms of RPS6KA2 with an alternative start codon. Homozygous deletions were identified within the RPS6KA2 gene in two cell lines. Re-expression of RPS6KA2 in ovarian cancer cell lines suppressed colony formation. In UCI101 cells, the expression of RPS6KA2 reduced proliferation, caused G1 arrest, increased apoptosis, reduced levels of phosphorylated extracellular signal-regulated kinase and altered other cell cycle proteins. In contrast, small interfering RNA against RPS6KA2 showed the opposite effect in 41M cells. The above results suggest that RPS6KA2 is a putative tumour suppressor gene to explain allele loss at 6q27.

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“…Work using PDK1 −/− embryonic stem cells confirmed that PDK1 was required for the activation of RSK1, RSK2 and RSK3 [20]. Surprisingly, however, the use of these knockout cells has also demonstrated that the activation of MSK1 [20] and RSK4 [21] is independent of PDK1, and that T-loop phosphorylation for these kinases occurs via a different mechanism.…”

Section: Introductionmentioning

confidence: 99%

Identification of novel phosphorylation sites in MSK1 by precursor ion scanning MS

McCoy

Macdonald

Morrice

et al. 2007

Biochemical Journal

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MSK1 (mitogen-and stress-activated kinase 1) is a dual kinase domain protein that acts downstream of the ERK1/2 (extracellular-signal-regulated kinase 1/2) and p38 MAPK (mitogenactivated protein kinase) signalling pathways in cells. MSK1, and its related isoform MSK2, phosphorylate the transcription factors CREB (cAMP-response-element-binding protein) and ATF1 (activating transcription factor 1), and the chromatin proteins histone H3 and HMGN1 (high-mobility-group nucleosomalbinding protein 1) in response to either mitogenic stimulation or cellular stress. MSK1 activity is tightly regulated in cells, and activation requires the phosphorylation of MSK1 by either ERK1/2 or p38α. This results in activation of the C-terminal kinase domain, which then phosphorylates further sites in MSK1, leading to the activation of the N-terminal kinase domain and phosphorylation of substrates. Here, we use precursor ion scanning MS to identify five previously unknown sites in MSK1: Thr 630 , Ser 647 , Ser 657 , Ser 695 and Thr 700 . One of these sites, Thr 700 , was found to be a third site in MSK1 phosphorylated by the upstream kinases ERK1/2 and p38α. Mutation of Thr 700 resulted in an increased basal activity of MSK1, but this could be further increased by stimulation with PMA or UV-C radiation. Surprisingly, however, mutation of Thr 700 resulted in a dramatic loss of Thr 581 phosphorylation, a site essential for activity. Mutation of Thr 700 and Thr 581 to an alanine residue resulted in an inactive kinase, while mutation of both sites to an aspartic acid residue resulted in a kinase with a significant basal activity that could not be further stimulated. Together these results are consistent with a mechanism by which Thr 700 phosphorylation relieves the inhibition of MSK1 by a C-terminal autoinhibitory helix and helps induce a conformational shift that protects Thr 581 from dephosphorylation.

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Functional Characterization of Human RSK4, a New 90-kDa Ribosomal S6 Kinase, Reveals Constitutive Activation in Most Cell Types

Cited by 101 publications

References 55 publications

Aberrant Expression of X-Linked Genes RbAp46, Rsk4, and Cldn2 in Breast Cancer

Aberrant Expression of X-Linked Genes RbAp46, Rsk4, and Cldn2 in Breast Cancer

RPS6KA2, a putative tumour suppressor gene at 6q27 in sporadic epithelial ovarian cancer

Identification of novel phosphorylation sites in MSK1 by precursor ion scanning MS

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