Nuclear PLC Beta 1 is required for 3T3-L1 adipocyte differentiation and regulates expression of the cyclin D3-cdk4 complex

A phosphoinositide signalling cycle is present in the nucleus, independent of that which occurs at the plasma membrane. The key enzyme involved in this cycle is phospholipase (PLC) beta 1. This nuclear cycle has been shown to be involved in both cell proliferation and differentiation. Here, we report that nuclear PLC beta 1 activity is upregulated during differentiation of 3T3-L1 adipocytes. During differentiation there are two phases of PLC beta 1 activity; the first occurs within 5 min of treatment with differentiation media, does not require new PLC beta 1 to enter the nucleus and is regulated by pERK and PKC alpha while the second phase occurs from day 2 of differentiation, requires new PLC beta 1 protein to enter the nucleus and is independent of regulation by pERK and PKC alpha. Over-expression with the PLC mutants, Delta mk (which lacks the ERK phosphorylation site) and M2B (which lacks the nuclear localisation sequence), revealed that both phases of PLC beta 1 activity are required for terminal differentiation to occur. Inhibition of PLC beta 1 activity prevents the upregulation of cyclinD3 and cdk4 protein, suggesting that PLC beta 1 plays a role in the control of the cell cycle during differentiation. These results indicate nuclear PLC beta 1 as a key regulator of adipocyte differentiation. (C) 2009 Elsevier Inc. All rights reserved.