Inositides in the nucleus: presence and characterisation of the isozymes of phospholipase β family in NIH 3T3 cells

Previous reports from our laboratories and others have hinted that the nucleus is a site for an autonomous signalling system acting through the activation of the inositol lipid cycle. Among phospholipases (PLC) it has been shown previously that PLCβ1 is specifically localised in the nucleus as well as at the plasma membrane. Using NIH 3T3 cells, it has been possible to obtain, with two purification strategies, in the presence or in the absence of Nonidet P-40, both intact nuclei still maintaining the outer membrane and nuclei completely stripped of their envelope. In these nuclei, we show that not only PLCβ1 is present, but also PLCβ2, PLCβ3 and PLCβ4. The more abounding isoform is PLCβ1 followed by PLCβ3, PLCβ2 and PLCβ4, respectively. All the isoforms are enriched in nuclear preparations free from nuclear envelope and cytoplasmatic debris, indicating that the actual localisation of the PLCβ isozymes is in the inner nuclear compartment.