Identification of Cyclin A2 as the Downstream Effector of the Nuclear Phosphatidylinositol 4,5-Bisphosphate Signaling Network

Abstract

In addition to the well characterized phosphoinositide second messengers derived from the plasma membrane, increasing evidence supports the existence of a nuclear phosphoinositide signaling network. The aim of this investigation was to dissect the role played by nuclear phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P 2 ) in cell cycle progression and to determine the cell cycle regulatory component(s) that are involved. A number of cytosolic/nuclear PtdIns(4,5)P 2 -deficient Swiss 3T3 cell lines were established, and their G 0 /G 1 /S cell cycle phase transitions induced by defined mitogens were examined. Our results demonstrate that nuclear PtdIns(4,5)P 2 down-regulation caused a delay in phorbol ester-induced S phase entry and that this was at least in part channeled through cyclin A 2 at the transcriptional level. In summary, these data identify cyclin A 2 as a downstream effector of the nuclear PtdIns(4,5)P 2 signaling network and highlight the importance of nuclear PtdIns(4,5)P 2 in the regulation of mammalian mitogenesis.Activation of diverse signal transduction pathways can cause quiescent cells to re-enter the cell cycle. Among these pathways, phosphoinositides (PIs) 2 represent a major class of mitogenic mediators. One of the recent developments in the field of PI signaling was the discovery of a discrete PI signaling network in the nucleus (1-4). Among the various PI species, phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P 2 ) is particularly important because it is the precursor molecule of diacylglycerol (DAG), inositol 1,4,5-trisphosphate (Ins(1,4,5)P 3 ), and phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P 3 ). The known signaling functions of nuclear PtdIns(4,5)P 2 include cell proliferation and differentiation, mRNA export/processing, chromatin remodeling, and transcriptional control (5-7). In addition, many of the PtdIns(4,5)P 2 -metabolizing enzymes such as phospholipase C (PLC), type II PI kinase, protein kinase C (PKC), DAG kinases, and PDK-1 have also been shown to exist in nuclei (5, 7).In Swiss 3T3 cells, stimulation with insulin-like growth factor I (IGF-I) causes a decrease in nuclear PtdIns(4)P and PtdIns(4,5)P 2 accompanied by an increase in nuclear DAG (6). These data contrasted with those obtained when cells are stimulated with the neuropeptide bombesin, which results in similar PI changes in the plasma membrane while the nuclear PI pool was unaffected (6). These results clearly demonstrate the distinct regulation of cytosolic and nuclear PtdIns(4,5)P 2 . More recently, the synchrony between cell cycle progression and nuclear PI turnover has been demonstrated (8, 10). The fact that nuclei isolated from Swiss 3T3 cells stimulated with IGF-I exhibit a decrease in PtdIns(4,5)P 2 accompanied by an increase in DAG strongly suggests the involvement of PLC activity (6). Indeed, it was later shown that nuclear PLC␤1 activity is upregulated 2-fold in Swiss 3T3 cells stimulated with IGF-I (11), and down-regulation of PLC␤-1 markedly reduces the sensitivity of Swiss 3T3 cells t...

Great Expectations for PIP: Phosphoinositides as Regulators of Signaling During Development and Disease

“…The previous sections highlight just a few examples of what we are beginning to learn about the diverse roles of phosphoinositides during development. The list of developmental processes that may depend upon regulated phosphatidylinositol metabolism can be expanded to include neurite extension and neuronal development, angiogenesis (Im and Kazlauskas, 2006), cytokinesis (Echard, 2008;Field et al, 2005;Wong et al, 2005), cell cycle regulation (Ho et al, 2008), and flagellar biogenesis (Wei et al, 2008) to name a few. Given their integral roles during development, it is not surprising that the misregulation of PIPs and PIP binding proteins has been implicated in a growing number of diseases and developmental disorders.…”

A polybasic motif in ErbB3-binding protein 1 (EBP1) has key functions in nucleolar localization and polyphosphoinositide interaction

“…PtdIns(4,5) P 2 was also shown to bind to BASP1 (brain acid soluble protein 1) and this interaction promotes a co-repressive function by recruiting histone deacetylases [ 43 ]. Other data correlate changes in the levels of nuclear PPIns to cell cycle progression [ 12 , 44 , 45 ] or apoptosis via an interaction between nucleophosmin (NPM) and PtdIns(3,4,5) P 3 [ 46 ].…”

The physiology and pathology of inositide signaling in the nucleus

“…In Swiss 3T3, it has been demonstrated that nuclear PtdIns(4,5)P 2 down-regulation caused a delay in phorbol ester-induced S phase entry and that this was at least in part channeled through cyclin A2 at the transcriptional level, identifying cyclin A2 as a downstream effector of the nuclear PtdIns(4,5)P 2 signaling network (Ho et al, 2008).…”