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Journal of Virology, April 2000, p. 3166-3176, Vol. 74, No. 7
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

E1A Blocks Hyperphosphorylation of p130 and p107 without Affecting the Phosphorylation Status of the Retinoblastoma Protein

Matilde Parreño, Judit Garriga, Ana Limón,dagger Xavier Mayol,Dagger George R. Beck Jr., Elizabeth Moran, and Xavier Graña*

Fels Institute for Cancer Research and Molecular Biology and Department of Biochemistry, Temple University School of Medicine, Philadelphia, Pennsylvania 19140

Received 17 September 1999/Accepted 30 December 1999

The phosphorylation status of the pRB family of growth suppressor proteins is regulated in a cell cycle entry-, progression-, and exit-dependent manner in normal cells. We have shown previously that p130, a member of this family, exhibits patterns of phosphorylated forms associated with various cell growth and differentiation stages. However, human 293 cells, which are transformed cells that express the adenoviral oncoproteins E1A and E1B, exhibit an abnormal pattern of p130 phosphorylated forms. Here we report that, unlike pRB, the phosphorylation status of both p130 and p107 is not modulated during the cell cycle in 293 cells as it is in other cells. Conditional overexpression of individual G1/S cyclins in 293 cells does not alter the phosphorylation status of p130, suggesting that the expression of E1A and/or E1B blocks hyperphosphorylation of p130. In agreement with these observations, transient cotransfection of vectors expressing E1A 12S, but not E1B, in combination with pocket proteins into U-2 OS cells blocks hyperphosphorylation of both p130 and p107. However, the phosphorylation status of pRB is not altered by cotransfection of E1A 12S vectors. Moreover, MC3T3-E1 preosteoblasts stably expressing E1A 12S also exhibit a block in hyperphosphorylation of endogenous p130 and p107. Direct binding of E1A to p130 and p107 is not required for the phosphorylation block since E1A 12S mutants defective in binding to the pRB family also block hyperphosphorylation of p130 and p107. Our data reported here identify a novel function of E1A, which affects p130 and p107 but does not affect pRB. Since E1A does not bind the hyperphosphorylated forms of p130, this function of E1A might prevent the existence of "free" hyperphosphorylated p130, which could act as a CDK inhibitor.

* Corresponding author. Mailing address: Fels Institute for Cancer Research and Molecular Biology, Temple University School of Medicine, AHP Bldg., Rm. 308, 3307 N. Broad St., Philadelphia, PA 19140. Phone: (215) 707-7416. Fax: (215) 707-5562/2102. E-mail: xavier{at}unix.temple.edu.

dagger Present address: Institut de Recerca Oncologica, 08907 Barcelona, Spain.

Dagger Present address: Unitat de Biologia Cellular i Molecular, Institut Municipal d'Investigació Medica, 08003 Barcelona, Spain.

Journal of Virology, April 2000, p. 3166-3176, Vol. 74, No. 7
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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