Phosphoinositide 3-kinase beta controls replication factor C assembly and function

Abstract

Genomic integrity is preserved by the action of protein complexes that control DNA homeostasis. These include the sliding clamps, trimeric protein rings that are arranged around DNA by clamp loaders. Replication factor C (RFC) is the clamp loader for proliferating cell nuclear antigen, which acts on DNA replication. Other processes that require mobile contact of proteins with DNA use alternative RFC complexes that exchange RFC1 for CTF18 or RAD17. Phosphoinositide 3-kinases (PI3K) are lipid kinases that generate 3-poly-phosphorylated-phosphoinositides at the plasma membrane following receptor stimulation. The two ubiquitous isoforms, PI3Kalpha and PI3Kbeta, have been extensively studied due to their involvement in cancer and nuclear PI3Kbeta has been found to regulate DNA replication and repair, processes controlled by molecular clamps. We studied here whether PI3Kbeta directly controls the process of molecular clamps loading. We show that PI3Kbeta associated with RFC1 and RFC1-like subunits. Only when in complex with PI3Kbeta, RFC1 bound to Ran GTPase and localized to the nucleus, suggesting that PI3Kbeta regulates RFC1 nuclear import. PI3Kbeta controlled not only RFC1– and RFC–RAD17 complexes, but also RFC–CTF18, in turn affecting CTF18-mediated chromatid cohesion. PI3Kbeta thus has a general function in genomic stability by controlling the localization and function of RFC complexes.

Alternative replication factor C protein, Elg1, maintains chromosome stability by regulating PCNA levels on chromatin

“…Elg1 might also be required for the recruitment of chromatin-associated proteins to the replication factory for the construction of the chromatin architecture as chromosome duplication proceeds. A previous report showed that Elg1 physically and genetically interacts with Rad27 (FEN1) (Kanellis et al 2003), and RFC1 and Ctf18 also interact with various proteins other than PCNA (Levin et al 2004;Franco et al 2005;Shiomi et al 2007;Farina et al 2008;Redondo-Munoz et al 2013).…”

Nuclear PI3K signaling in cell growth and tumorigenesis

“…PCNA requires the ATPase activity of the clamp loader, replication factor C (RFC), to open and encircle double-stranded DNA (Indiani and O'Donnell, 2006 ). Through a kinase-independent function, p110β was found to interact with RFC1, a subunit of the RFC complex, and thereby promote loading of PCNA onto chromatin (Redondo-Muñoz et al, 2013 ). It is interesting to note that p110β regulates PCNA loading through both kinase-dependent and -independent activities as phosphorylation of the cell cycle inhibitor p21 Cip1 on T145 releases PCNA from its suppressive binding to p21 Cip1 (Marqués et al, 2009 ).…”

“…It is interesting to note that p110β regulates PCNA loading through both kinase-dependent and -independent activities as phosphorylation of the cell cycle inhibitor p21 Cip1 on T145 releases PCNA from its suppressive binding to p21 Cip1 (Marqués et al, 2009 ). Depletion of p110β with RNA interference (RNAi) increased the expression levels of p21 Cip1 and its association with PCNA, and impaired PCNA-RFC association and loading onto chromatin (Marqués et al, 2009 ; Redondo-Muñoz et al, 2013 ). The interaction of PCNA and p21 Cip1 , occurring through the same domain as the PCNA-DNA pol δ interaction, negatively regulates S-phase progression (Cazzalini et al, 2003 ).…”

Nuclear phosphoinositides and their impact on nuclear functions

“…Furthermore, both the activity and scaffolding functions of P110β also facilitate DNA repair after DNA damage induced by ionizing radiation. NBN is a critical sensor of DNA damage, localizes to DNA damage‐induced foci, and is required for recruitment of protein complexes that affect DNA repair . NBN interacts with p110 β, and NBN localization at DNA damage‐induced foci is severely reduced when p110β is depleted.…”