The retinoblastoma tumor suppressor, RB, is inactivated in the majority of human cancers, resulting in growth advantage. While the underlying basis of inactivation encompasses a variety of mechanisms (e.g. deregulated phosphorylation, direct oncoprotein binding, point mutation) all of these results in disruption of RB assembled complexes. When active, RB is hypophosphorylated and assembles complexes that are capable of repressing transcription and inhibiting DNA replication. Mitogenic signaling cascades or oncogenic lesions stimulate phosphorylation of RB, thereby disrupting the assembled complexes and enabling progression through S-phase. In contrast, anti-mitogenic signals (e.g. DNA damage) prevent phosphorylation and maintain RB-repressor complexes, thus inhibiting cellular proliferation. Therefore, understanding RB-mediated replication control is germane both to regulated cell cycle progression (i.e. the interplay of mitogenic and anti-mitogenic signaling) and tumorigenesis. RB controls the expression and activity associated with several key factors requisite for DNA replication. Specifically, we have demonstrated that acute RB activation results in two events that result in the cessation of efficient DNA replication. First, RB inhibits expression of Cyclin A, a critical mediator of DNA replication. Attenuation of Cyclin A is causally associated with inhibition of PCNA activity that is required for DNA replication. In addition to this relatively rapid mechanism, long-term RB activation results in replicative exit and the loss of multiple components of the replication machinery (e.g. MCM2 and MCM7). Together, our prior studies put forth the hypothesis that RB-mediated replication control is a central means through which RB regulates proliferation and executes the appropriate response to DNA damage. This action of RB is achieved through two temporally distinct mechanisms.
In Aim I, we dissect the rapid action of RB on replication control through the identification of possible direct mechanisms and through the mechanistic analyses of Cyclin A/PCNA signaling axis.
In Aim II, we determine the influence of prolonged RB activation on replication competence and those replication complexes that demarcate functional origins. In both contexts (Aims I and II), we will determine how RB loss enables DNA replication following acute vs. prolonged DNA damage. Lastly, we will determine the action of RB in an in vivo model of physiologically regulated DNA replication and the consequence of RB loss in tumor progression. As such these studies evaluate the action of RB-mediated replication control as a means to limit proliferation, modify the response to DNA damage, and suppress tumorigenesis.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA106471-02
Application #
6878597
Study Section
Cancer Etiology Study Section (CE)
Program Officer
Spalholz, Barbara A
Project Start
2004-08-01
Project End
2009-05-31
Budget Start
2005-08-01
Budget End
2006-05-31
Support Year
2
Fiscal Year
2005
Total Cost
$247,825
Indirect Cost
Name
University of Cincinnati
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
041064767
City
Cincinnati
State
OH
Country
United States
Zip Code
45221
McClendon, A Kathleen; Dean, Jeffry L; Ertel, Adam et al. (2010) Differential impact of tumor suppressor pathways on DNA damage response and therapy-induced transformation in a mouse primary cell model. PLoS One 5:e8558
Braden, W A; McClendon, A K; Knudsen, E S (2008) Cyclin-dependent kinase 4/6 activity is a critical determinant of pre-replication complex assembly. Oncogene 27:7083-93
Reed, Michael F; Zagorski, William A; Knudsen, Erik S (2007) RB activity alters checkpoint response and chemosensitivity in lung cancer lines. J Surg Res 142:364-72
Zagorski, William A; Knudsen, Erik S; Reed, Michael F (2007) Retinoblastoma deficiency increases chemosensitivity in lung cancer. Cancer Res 67:8264-73
Srinivasan, Seetha V; Mayhew, Christopher N; Schwemberger, Sandy et al. (2007) RB loss promotes aberrant ploidy by deregulating levels and activity of DNA replication factors. J Biol Chem 282:23867-77
Mayhew, Christopher N; Carter, Scott L; Fox, Sejal R et al. (2007) RB loss abrogates cell cycle control and genome integrity to promote liver tumorigenesis. Gastroenterology 133:976-84
Seeley, Sarah L; Bosco, Emily E; Kramer, Elizabeth et al. (2007) Distinct roles for RB loss on cell cycle control, cisplatin response, and immortalization in Schwann cells. Cancer Lett 245:205-17
Bosco, Emily E; Wang, Ying; Xu, Huan et al. (2007) The retinoblastoma tumor suppressor modifies the therapeutic response of breast cancer. J Clin Invest 117:218-28
Bosco, Emily E; Knudsen, Erik S (2007) RB in breast cancer: at the crossroads of tumorigenesis and treatment. Cell Cycle 6:667-71
Knudsen, Erik S; Sexton, Charlene R; Mayhew, Christopher N (2006) Role of the retinoblastoma tumor suppressor in the maintenance of genome integrity. Curr Mol Med 6:749-57

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