PLCβ1 by-passes early growth response-1 to induce the differentiation of neuronal cells

The G alpha q/phospholipase C-beta (PLC beta) signaling system mediates calcium responses to a variety of hormones and neurotransmitters. Recent studies suggest that PLC beta 1 expression plays a role in the differentiation of two types of cultured neuronal cells (PC12 and SK-N-SH) through a mechanism independent of G alpha q. Here, we show that, similar to that observed in PC12 and SK-N-SH cells, PLC beta 1 expression increases when human NT2 cells are induced to differentiate either through cytosine-beta-D-arabinofuranoside or retinoic acid. Preventing this increase, abolishes differentiation, and down-regulating PLC beta 1 in rat primary astrocytes causes cells to adapt an undifferentiated morphology. Surprisingly, transfecting PLC beta 1 into undifferentiated PC12 or NT2 cells induces differentiation without the need for differentiating agents. Studies to uncover the underlying mechanism focused on the transcription factor early growth response 1 (Egr-1) which mediates PLC beta 1 expression early in differentiation. Over-expressing PLC beta 1 in HEK293 cells enhances Egr-1 expression and induces morphological changes. We show that increased levels of cytosolic PLC beta 1 in undifferentiated PC12 cells disrupts the association between Egr-1 and its cytosolic binding partner (Tar RNA binding protein), promoting relocalization of Egr-1 to the nucleus, which promotes transcription of proteins needed for differentiation. These studies show a novel mechanism through which differentiation can be modulated.