scholarly journals Identification of Xenopus S6 protein kinase homologs (pp90rsk) in somatic cells: phosphorylation and activation during initiation of cell proliferation.

1990 ◽  
Vol 10 (6) ◽  
pp. 3204-3215 ◽  
Author(s):  
R H Chen ◽  
J Blenis
Keyword(s):  
Cell Proliferation ◽  
Protein Kinase ◽  
Protein Phosphorylation ◽  
Cultured Cells ◽  
Animal Cell ◽  
Somatic Cells ◽  
Cross Reactivity ◽  
S6 Kinase ◽  
Quiescent Cells ◽  
Molecular Sizes

We have identified human, mouse, and chicken homologs to Xenopus S6 protein kinase II (S6KII). In quiescent cells, the apparent molecular mass of the Xenopus homologs (referred to as pp90rsk) increased from a range of 81 to 91 to a range of 85 to 92 kilodaltons following serum addition, which is consistent with an increase in protein phosphorylation. Indeed, serum growth factors stimulated pp90rsk phosphorylation at multiple serine and threonine residues. Furthermore, pp90rsk activity was stimulated within seconds of serum addition. Distinct molecular sizes, chromatographic properties, phosphopeptide maps, and kinetics of activation, the lack of immunological cross-reactivity, and analysis of S6 kinase activities in cells that overexpressed pp90rsk suggest that pp90rsk and pp70-S6 protein kinase, a previously identified mitogen- and oncogene-regulated S6 kinase in cultured cells, are distinct and differentially regulated. The notion that both enzymes are regulated by protein phosphorylation was supported by the ability to inactivate their S6 phosphotransferase activities with potato acid phosphatase. These data demonstrate that homologs to the Xenopus S6 protein kinases are produced and regulated by protein phosphorylation in somatic cells and that, in addition to a proposed role in Xenopus oocyte maturation, these homologs may participate in the initiation of animal cell proliferation.

Identification of Xenopus S6 protein kinase homologs (pp90rsk) in somatic cells: phosphorylation and activation during initiation of cell proliferation

1990 ◽  
Vol 10 (6) ◽  
pp. 3204-3215
Author(s):  
R H Chen ◽  
J Blenis
Keyword(s):  
Cell Proliferation ◽  
Protein Kinase ◽  
Protein Phosphorylation ◽  
Cultured Cells ◽  
Animal Cell ◽  
Somatic Cells ◽  
Cross Reactivity ◽  
S6 Kinase ◽  
Quiescent Cells ◽  
Molecular Sizes

We have identified human, mouse, and chicken homologs to Xenopus S6 protein kinase II (S6KII). In quiescent cells, the apparent molecular mass of the Xenopus homologs (referred to as pp90rsk) increased from a range of 81 to 91 to a range of 85 to 92 kilodaltons following serum addition, which is consistent with an increase in protein phosphorylation. Indeed, serum growth factors stimulated pp90rsk phosphorylation at multiple serine and threonine residues. Furthermore, pp90rsk activity was stimulated within seconds of serum addition. Distinct molecular sizes, chromatographic properties, phosphopeptide maps, and kinetics of activation, the lack of immunological cross-reactivity, and analysis of S6 kinase activities in cells that overexpressed pp90rsk suggest that pp90rsk and pp70-S6 protein kinase, a previously identified mitogen- and oncogene-regulated S6 kinase in cultured cells, are distinct and differentially regulated. The notion that both enzymes are regulated by protein phosphorylation was supported by the ability to inactivate their S6 phosphotransferase activities with potato acid phosphatase. These data demonstrate that homologs to the Xenopus S6 protein kinases are produced and regulated by protein phosphorylation in somatic cells and that, in addition to a proposed role in Xenopus oocyte maturation, these homologs may participate in the initiation of animal cell proliferation.

Requirement of Androgen-Dependent Activation of Protein Kinase Cζ for Androgen-Dependent Cell Proliferation in LNCaP Cells and Its Roles in Transition to Androgen-Independent Cells

2006 ◽  
Vol 20 (12) ◽  
pp. 3053-3069 ◽  
Author(s):  
Takahiro Inoue ◽  
Toru Yoshida ◽  
Yosuke Shimizu ◽  
Takashi Kobayashi ◽  
Toshinari Yamasaki ◽  
...  
Keyword(s):  
Prostate Cancer ◽  
Cell Proliferation ◽  
Protein Kinase ◽  
Cell Line ◽  
Kinase Activity ◽  
Mammalian Target Of Rapamycin ◽  
Lncap Cells ◽  
S6 Kinase ◽  
P70 S6 Kinase ◽  
Androgen Independent

Abstract A cell line that we designed, AILNCaP, proliferated in androgen-depleted medium after emerging from long-term androgen-depleted cultures of an androgen-sensitive prostate cancer cell line, LNCaP. Using this cell line as a model of progression to androgen independence, we demonstrated that the activity of the mammalian target of rapamycin/p70 S6 kinase transduction pathway is down-regulated after androgen depletion in LNCaP, whereas its activation is related to transition of this cell line to androgen-independent proliferation. Kinase activity of protein kinase Cζ is regulated by androgen stimulation in LNCaP cells, whereas it is activated constitutively in AILNCaP cells under androgen-depleted conditions. Treatment with a protein kinase Cζ pseudosubstrate inhibitor reduced p70 S6 kinase activity and cell proliferation in both cell lines. We identified that both protein kinase Cζ and p70 S6 kinase were associated in LNCaP cells and this association was enhanced by the androgen stimulation. We examined the expression of phospho-protein kinase Cζ and phospho-p70 S6 kinase in hormone-naive prostate cancer specimens and found that the expression of both kinases was correlated with each other in those specimens. Significant correlation was observed between the expression of both kinases and Ki67 expression. Most of the prostate cancer cells that survived after prior hormonal treatment also expressed both kinases. This is the first report that shows the significance of this pathway for both androgen-dependent and -independent cell proliferation in prostate cancer. Our data suggest that protein kinase Cζ/mammalian target of rapamycin/S6 kinase pathway plays an important role for the transition of androgen-dependent to androgen-independent prostate cancer cells.

scholarly journals Follicle-Stimulating Hormone Inhibits Adenosine 5′-Monophosphate-Activated Protein Kinase Activation and Promotes Cell Proliferation of Primary Granulosa Cells in Culture through an Akt-Dependent Pathway

Endocrinology ◽  
2009 ◽  
Vol 150 (2) ◽  
pp. 929-935 ◽  
Author(s):  
Pradeep P. Kayampilly ◽  
K. M. J. Menon
Keyword(s):  
Cell Cycle ◽  
Cell Proliferation ◽  
Protein Kinase ◽  
Mrna Expression ◽  
Granulosa Cell ◽  
Granulosa Cells ◽  
Ampk Activation ◽  
Cyclin D2 ◽  
Cell Cycle Inhibitor ◽  
Dependent Pathway

FSH, acting through multiple signaling pathways, regulates the proliferation and growth of granulosa cells, which are critical for ovulation. The present study investigated whether AMP-activated protein kinase (AMPK), which controls the energy balance of the cell, plays a role in FSH-mediated increase in granulosa cell proliferation. Cells isolated from immature rat ovaries were grown in serum-free, phenol red free DMEM-F12 and were treated with FSH (50 ng/ml) for 0, 5, and 15 min. Western blot analysis showed a significant reduction in AMPK activation as observed by a reduction of phosphorylation at thr 172 in response to FSH treatment at all time points tested. FSH also reduced AMPK phosphorylation in a dose-dependent manner with maximum inhibition at 100 ng/ml. The chemical activator of AMPK (5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside, 0.5 mm) increased the cell cycle inhibitor p27 kip expression significantly, whereas the AMPK inhibitor (compound C, 20 μm) and FSH reduced p27kip expression significantly compared with control. FSH treatment resulted in an increase in the phosphorylation of AMPK at ser 485/491 and a reduction in thr 172 phosphorylation. Inhibition of Akt phosphorylation using Akt inhibitor VIII reversed the inhibitory effect of FSH on thr 172 phosphorylation of AMPK, whereas ERK inhibitor U0126 had no effect. These results show that FSH, through an Akt-dependent pathway, phosphorylates AMPK at ser 481/495 and inhibits its activation by reducing thr 172 phosphorylation. AMPK activation by 5-amino-imidazole-4-carboxamide-1-β-d-ribofuranoside treatment resulted in a reduction of cell cycle regulatory protein cyclin D2 mRNA expression, whereas FSH increased the expression by 2-fold. These results suggest that FSH promotes granulosa cell proliferation by increasing cyclin D2 mRNA expression and by reducing p27 kip expression by inhibiting AMPK activation through an Akt-dependent pathway. FSH stimulates granulosa cell proliferation by reducing cell cycle inhibitor p27 kip through AMP kinase inhibition.

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