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Involvement of nuclear PLCβ1 in lamin B1 phosphorylation and G₂/M cell cycle progression

Cellular Signaling Laboratory, Department of Human Anatomical Sciences, University of Bologna, Bologna, Italy

¹Correspondence: Cellular Signaling Laboratory, Department of Human Anatomical Sciences, University of Bologna, Via Irnerio 48, 40126 Bologna, Italy. E-mail: lucio.cocco{at}unibo.it

Inositide-specific phospholipase Cβ1 (PLCβ1) signaling in cell proliferation has been investigated thoroughly in the G₁ cell cycle phase. However, little is known about its involvement in G₂/M progression. We used murine erythroleukemia cells to investigate the role of PLCβ1 in G₂/M cell cycle progression and screened a number of candidate intermediate players, particularly mitogen-activated protein kinase (MAPK) and protein kinase C (PKC), which can, potentially, transduce serum mitogenic stimulus and induce lamin B1 phosphorylation, leading to G₂/M progression. We report that PLCβ1 colocalizes and physically interacts with lamin B1. Studies of the effects of inhibitors and selective si-RNA mediated silencing showed a role of JNK, PKC, PKCβI, and the β1 isoform of PI-PLC in cell accumulation in G₂/M [as observed by fluorescence-activated cell sorter (FACS)]. To shed light on the mechanism, we considered that the final signaling target was lamin B1 phosphorylation. When JNK, PKC, or PLCβ1 were silenced, lamin B1 exhibited a lower extent of phosphorylation, as compared to control. The salient features to emerge from these studies are a common pathway in which JNK is likely to represent a link between mitogenic stimulus and activation of PLCβ1, and, foremost, the finding that the PLCβ1-mediated pathway represents a functional nuclear inositide signaling in the G₂/M transition.— Fiume, R., Ramazzotti, G., Teti, G., Chiarini, F., Faenza, I., Mazzotti, G., Billi, A. M., Cocco, L., Involvement of nuclear PLCβ1 in lamin B1 phosphorylation and G₂/M cell cycle progression.

Key Words: JNK • PKC • nucleus • inositide signaling

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