Cell Cycle-Dependent Switch of TopBP1 Functions by Cdk2 and Akt

ABSTRACT

Cdk2-dependent TopBP1-treslin interaction is critical for DNA replication initiation. However, it remains unclear how this association is terminated after replication initiation is finished. Here, we demonstrate that phosphorylation of TopBP1 by Akt coincides with cyclin A activation during S and G₂ phases and switches the TopBP1-interacting partner from treslin to E2F1, which results in the termination of replication initiation. Premature activation of Akt in G₁ phase causes an early switch and inhibits DNA replication. TopBP1 is often overexpressed in cancer and can bypass control by Cdk2 to interact with treslin, leading to enhanced DNA replication. Consistent with this notion, reducing the levels of TopBP1 in cancer cells restores sensitivity to a Cdk2 inhibitor. Together, our study links Cdk2 and Akt pathways to the control of DNA replication through the regulation of TopBP1-treslin interaction. These data also suggest an important role for TopBP1 in driving abnormal DNA replication in cancer.

KEYWORDS:

• TopBP1
• treslin
• Akt
• cyclin A
• Cdk2

ACKNOWLEDGMENTS

We thank William Dunphy for providing treslin constructs.

This work was supported by NIH grants R01CA100857 (to W.-C.L.) and R01CA203824 and Department of Defense grants W81XWH-14-1-0306, W81XWH-14-1-0339, W81XWH-18-1-0329, and W81XWH-19-1-0369 (to W.-C.L. and F.-T.L.). J.D.G. was supported by T32 Fellowship T32DK060445. We also acknowledge support from the Cytometry and Cell Sorting Core (NIAID P30AI036211, NCI P30CA125123, and NCRR S10RR024574) at Baylor College of Medicine.

W.-C.L. conceived the project; K.L. and W.-C.L. designed research; K.L. performed most experiments; J.D.G., and Y.-J.L. performed BrdU/PI flow cytometry analysis; F.-T.L. and W.-C.L. contributed new reagents/analytic tools; W.-C.L. performed data mining; K.L., J.D.G., Y.-J.L., F.-T.L. and W.-C.L. analyzed data; and K.L., F.-T.L., and W.-C.L. wrote the paper. W.-C.L. and F.-T.L. acquired funding.

We all declare that we have no financial interests that pose a conflict of interest regarding the article.