SIGNAL-TRANSDUCTION THROUGH EPIDERMAL GROWTH-FACTOR RECEPTOR IS ALTERED IN HELA MONOLAYER CELLS DURING MITOSIS

Epidermal growth factor (EGF)-induced signalling was studied separatel y in the mitosis and GZ-phases of HeLa monolayer cells presynchronized (1) by amethopterin inhibition and thymidine release or (2) by nocoda zole. For comparison, cells were treated with the phorbol ester phorbo l 12-myristate 13-acetate (PMA). In contrast with the observed respons es effected by PMA, which seem to be independent of cell cycle and syn chronization conditions, those induced by EGF are greatly influenced b y both criteria. Synchronization with nocodazole abolished the EGF-ind uced stimulation of phosphoinositide hydrolysis in G2 as well as in mi totic cells although tyrosine phosphorylation of the EGF receptor and phospholipase C gamma 1 could be shown to occur, especially in G2 cell s. Synchronization with amethopterin/ thymidine showed that, in contra st with G2 cells, mitotic cells were not able to react to EGF with an increase in phosphoinositide hydrolysis although a certain degree of E GF receptor dimerization and autophosphorylation as well as tyrosine p hosphorylation of phospholipase C gamma 1 could still be shown to occu r in mitosis. The results seem to indicate that the EGF pathway leadin g to a stimulation of phosphoinositide hydrolysis is attenuated at dif ferent levels and requires a cytoskeletal condition that is not presen t either after treatment (24 h) with nocodazole or during normal mitos is of a monolayer cell.