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Regulation of Skp2 promoter activity by PI3K and NFkB during preadipocyte proliferation
Author(s) -
Auld Corinth A,
Caccia Carla D,
Morrison Ron F
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a164-c
Subject(s) - pi3k/akt/mtor pathway , skp2 , microbiology and biotechnology , messenger rna , proteasome , ubiquitin ligase , cell cycle , chemistry , mapk/erk pathway , biology , signal transduction , ubiquitin , cell , biochemistry , gene
We have shown that the cell cycle inhibitor p27 is rapidly degraded by the F‐box protein Skp2 in conjunction with the SCFE3 Ligase and 26S proteasome during the early stages of adipocyte differentiation. After stimulation with the differentiation cocktail, Skp2 expression peaks during S phase and decreases prior to terminal differentiation. Interestingly, Skp2 cannot be induced in fully differentiated adipocytes when restimulated with the same differentiation cocktail. To understand how this unique increase in Skp2 occurs, we examined mRNA and protein levels and found that, while translational and post‐translational events may occur, the majority of regulation is through increases in mRNA. Further studies revealed that after cells are stimulated to differentiate, there are significant changes in Skp2 promoter activity with absolutely no change in mRNA stability. An evaluation of the individual components of the stimulation cocktail showed that insulin, at a concentration known to activate the IGF‐1 receptor, plays the predominant role in upregulating Skp2 expression. Therefore, we examined the involvement of PI3K and MAPK signaling cascades and found that while there is a synergistic effect of the two, inhibiting the PI3K pathway has the most dramatic effect on Skp2 mRNA and protein levels. NFkB p65 and p50 heterodimers are transcription factors whose expression and activity can be increased by the aforementioned pathways and are also known to play a role in promoting cell cycle progression. Using a potent and specific inhibitor, Helenalin, we found that NFkB p65 DNA‐binding is required for Skp2 expression. Work supported by grants from American Heart Association (0265418U) and NIH (1R21DK072067‐01).