Abstract
The REC2 recombinase is essential for recombinational repair following DNA damage as well as for successful meiosis and gene targeting in the corn smut Ustilago maydis. Here we report that overexpression of REC2 induced apoptotic cell death in human HuH-7, Hep G2, and Hep 3B hepatoma cells. Apoptosis was related to recombinase activity and was significantly increased by inhibition of retinoblastoma (Rb) expression with transforming growth factor-beta1. REC2-induced apoptosis was associated with a significantly reduced percentage of cells in the G1 phase of the cell cycle and a significant reduction in G2/M only in the Rb(-/-) Hep 3B cells. Overexpression of REC2 resulted in increased abundance of the hyperphosphorylated form of Rb. However, by immunoprecipitation REC2 was associated primarily with hypophosphorylated Rb, suggesting that REC2 may be involved in modulating the phosphorylation state of Rb. The A and B pocket domains with the spacer amino acid sequence and the carboxyl-terminal region of Rb were required for maximal binding to REC2. Overexpression of Rb significantly inhibited REC2-induced apoptosis even in the presence of transforming growth factor-beta1. Taken together, these data suggest a novel interaction of Rb with the recombinase REC2 and a role for this complex in bridging DNA recombination and apoptosis.
Highlights
The retinoblastoma tumor suppressor gene product (Rb) is a nuclear phosphoprotein that is involved in regulating progression through the cell cycle [1]
Our results indicate that overexpression of REC2 is associated with an increase in apoptosis that is regulated in part by the level of recombinase activity
Results are the means 6 S.D. of at least three separate experiments expressed as the percentage of total cells in the designated phase of the cell cycle determined by flow cytometry as described under “Experimental Procedures.”
Summary
The retinoblastoma tumor suppressor gene product (Rb) is a nuclear phosphoprotein that is involved in regulating progression through the cell cycle [1]. Overexpression of REC2 resulted in increased abundance of the hyperphosphorylated form of Rb. by immunoprecipitation REC2 was associated primarily with hypophosphorylated Rb, suggesting that REC2 may be involved in modulating the phosphorylation state of Rb. The A and B pocket domains with the spacer amino acid sequence and the carboxyl-terminal region of Rb were required for maximal binding to REC2.
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