p90 Ribosomal S6 Kinase and p70 Ribosomal S6 Kinase Link Phosphorylation of the Eukaryotic Chaperonin Containing TCP-1 to Growth Factor, Insulin, and Nutrient Signaling

Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 04/2009; 284(22):14939-48. DOI: 10.1074/jbc.M900097200
Source: PubMed


Chaperonin containing TCP-1 (CCT) is a large multisubunit complex that mediates protein folding in eukaryotic cells. CCT participates in the folding of newly synthesized polypeptides, including actin, tubulin, and several cell cycle regulators; therefore, CCT plays an important role in cytoskeletal organization and cell division. Here we identify the chaperonin CCT as a novel physiological substrate for p90 ribosomal S6 kinase (RSK) and p70 ribosomal S6 kinase (S6K). RSK phosphorylates the beta subunit of CCT in response to tumor promoters or growth factors that activate the Ras-mitogen-activated protein kinase (MAPK) pathway. CCTbeta Ser-260 was identified as the RSK site by mass spectrometry and confirmed by site-directed mutagenesis. RSK-dependent Ser-260 phosphorylation was sensitive to the MEK inhibitor UO126 and the RSK inhibitor BID-1870. Insulin weakly activates RSK but strongly activates the phosphoinositide 3-kinase (PI3K)-mammalian target of rapamycin (mTOR) pathway and utilizes S6K to regulate CCTbeta phosphorylation. Thus, the Ras-MAPK and PI3K-mTOR pathways converge on CCTbeta Ser-260 phosphorylation in response to multiple agonists in various mammalian cells. We also show that RNA interference-mediated knockdown of endogenous CCTbeta causes impaired cell proliferation that can be rescued with ectopically expressed murine CCTbeta wild-type or phosphomimetic mutant S260D, but not the phosphorylation-deficient mutant S260A. Although the molecular mechanism of CCTbeta regulation remains unclear, our findings demonstrate a link between oncogene and growth factor signaling and chaperonin CCT-mediated cellular activities.

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    • "Therefore , CCT6a seems to be differentially regulated by MMP-3, possibly by a modification at the transcriptional or/and post-translational level. CCT6a is a member of the eukaryotic cytosolic chaperonin containing TCP-1 (CCT) complex that mediates folding of various proteins such as actin and tubulin (Fig. 3; Abe et al., 2009). To investigate whether CCT6a is the only subunit that has undergone MMP-3- dependent modifications during development of the cerebellum, Western blotting was also performed for several other CCT subunits, more specifically CCT3, 4, 5, 6b, and 7. Yet, no genotypic differences in expression level or in molecular weight could be observed for any of these CCT subunits [Figure 4 "
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    • "CCT is composed of eight different subunits (1, 2, 3, 4, 5, 6, 7, and 8) and their functions are poorly understood [22]. Previous studies showed that CCT2 expression was important for normal cell proliferation [23], [24]. Moreover, CCT2 is overexpressed in certain malignant tumors and its overexpression is closely correlated with poor prognosis [25]. "
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