Abstract
Understanding inhibitory mechanisms of transforming growth factor beta1 (TGF-beta1) has provided insight into cell cycle regulation and how TGF-beta1 sensitivity is lost during tumorigenesis. We show here that TGF-beta1 utilizes a previously unknown mechanism targeting the function of prereplication complexes (pre-RCs) to acutely block S-phase entry when added to cells in late G(1), after most G(1) events have occurred. TGF-beta1 treatment in early G(1) suppresses Myc and CycE-Cdk2 and blocks pre-RC assembly. However, TGF-beta1 treatment in late G(1) acutely blocks S-phase entry by inhibiting activation of fully assembled pre-RCs, with arrest occurring prior to the helicase unwinding step at G(1)/S. This acute block by TGF-beta1 requires the function of Rb in late G(1) but does not involve Myc/CycE-Cdk2 suppression or transcriptional control. Instead, Rb mediates TGF-beta1 late-G(1) arrest by targeting the MCM helicase. Rb binds the MCM complex during late G(1) via a direct interaction with Mcm7, and TGF-beta1 blocks their dissociation at G(1)/S. Loss of Rb or overexpression of Mcm7 or its Rb-binding domain alone abrogates late-G(1) arrest by TGF-beta1. These results demonstrate that TGF-beta1 acutely blocks entry into S phase by inhibiting pre-RC activation and suggest a novel role for Rb in mediating this effect of TGF-beta1 through direct interaction with and control of the MCM helicase.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Cell Cycle Proteins / antagonists & inhibitors
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Cell Cycle Proteins / metabolism*
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Cell Line
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Cyclin A / antagonists & inhibitors
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Cyclin A / metabolism
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Cyclin E / antagonists & inhibitors
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Cyclin E / metabolism
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Cyclin-Dependent Kinase 2 / antagonists & inhibitors
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Cyclin-Dependent Kinase 2 / metabolism
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DNA-Binding Proteins / antagonists & inhibitors
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DNA-Binding Proteins / metabolism*
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Dichlororibofuranosylbenzimidazole / pharmacology
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Enzyme Inhibitors / pharmacology
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G1 Phase / drug effects*
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G1 Phase / physiology
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Humans
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Mice
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Minichromosome Maintenance Complex Component 7
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Nuclear Proteins / antagonists & inhibitors
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Nuclear Proteins / metabolism*
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Protein Serine-Threonine Kinases / antagonists & inhibitors
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Protein Serine-Threonine Kinases / metabolism
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RNA Polymerase II / antagonists & inhibitors
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RNA Polymerase II / metabolism
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Retinoblastoma Protein / metabolism*
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S Phase / drug effects*
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S Phase / physiology
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Transforming Growth Factor beta1 / pharmacology*
Substances
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Cell Cycle Proteins
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Cyclin A
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Cyclin E
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DNA-Binding Proteins
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Enzyme Inhibitors
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Nuclear Proteins
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Retinoblastoma Protein
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Transforming Growth Factor beta1
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Dichlororibofuranosylbenzimidazole
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Cdc7 protein, mouse
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Protein Serine-Threonine Kinases
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Cdk2 protein, mouse
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Cyclin-Dependent Kinase 2
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RNA Polymerase II
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Mcm7 protein, mouse
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Minichromosome Maintenance Complex Component 7