Interactions between the RNA Interference Effector Protein Ago1 and 14-3-3 Proteins

Abstract

Here, we provide evidence that the amino terminus of Ago1 binds to proteins that function in cell cycle regulation including 14-3-3 proteins. Interestingly, the amino terminus of human Ago2, the endonuclease that cleaves siRNA-targeted mRNAs, was also demonstrated to bind 14-3-3 proteins. Overexpression of the Ago1 amino terminus in yeast resulted in cell cycle delay at the G 2 /M boundary. Further investigation revealed that nuclear import of the mitosis-inducing phosphatase Cdc25 is inhibited by overexpression of the Ago1 amino terminus. Under these conditions, we found that the cyclin-dependent kinase Cdc2 is constitutively phosphorylated on tyrosine 15, thereby reducing the activity of this kinase, a situation that delays entry into mitosis. We hypothesize that 14-3-3 proteins are required for Argonaute protein functions in cell cycle and/or gene-silencing pathways.

Effect of betulinic acid on the regulation of Hiwi and cyclin B1 in human gastric adenocarcinoma AGS cells

“…BA also induced distinct G 2 /M phase arrest and apoptosis in AGS cells, accompanied with typical apoptotic morphological changes. It have been revealed numerous pro-apoptosis and cell cycle proteins (eg, Cyclin B1, CyclinD1 and Bcl-x L ) were targeted by BA [15][16][17] . Because Bcl-x L , Cyclin D1 and Cyclin B1 gene expression modulated by BA is regulated by Piwi protein, we investigated whether the anticarcinogenic effect of BA was mediated through modulation of Hiwi and Hiwi-regulated gene products.…”

“…Overexpression of the Piwi in yeast resulted in cell cycle delay at the G 2 /M boundary [17] . For example in Drosophila, altering the expression level of Piwi leads to changes in the proliferation rate of germline stem cells [18] .…”

“…Therefore how BA-mediated cell cycle changes are linked to its antitumor activity remains to be addressed. Since bcl-X L , p21, Cyclin D1, and Cdc2-Cyclin B complex expression modulated by BA are also regulated by Hiwi [15][16][17] , it is very possible that BA exerts its antitumor effect through directly affecting a major target Hiwi and then indirectly impacting other factors.…”

“…Genetic and biochemical studies first linked Piwi proteins to signaling processes that affect cellular differentiation and development [18] . In addition, numerous groups have shown that Piwi proteins function as part of the RNAi machinery to mediate posttranscriptional gene, chromatin silencing and cell cycle regulation [17,19] . Moreover, Piwi proteins are proved to serve as effector molecules that provide specificity in gene-silencing pathways [20] .…”

RNA Interference in Trypanosoma brucei

“…For instance, genetic analyses of patterning and morphogenesis in Drosophila embryos have revealed an essential role for the N-terminal glutamine-rich repeats of AGO2-slicer (11) and the N-terminal half of Schizosaccharomyces pombe AGO1, including the PAZ domain, has been shown to bind to proteins involved in cellcycle regulation (12). Furthermore, in vivo studies from our laboratory have indicated that the N-terminal 68 amino acids of Trypanosoma brucei AGO1 (termed the RGG domain, because it includes ten arginine-glycine-glycine or RGG motifs) is an important determinant for the RNAi response (13).…”