GROWTH-FACTORS STIMULATE PHOSPHORYLATION OF CTP-PHOSPHOCHOLINE CYTIDYLYLTRANSFERASE IN HELA-CELLS

The effect of insulin and epidermal growth factor on the phosphorylati on of CTP:phosphocholine cytidylyltransferase (EC 2.7.7.15) was invest igated in HeLa cells. For the first time, cytidylyltransferase phospho rylation was shown to be influenced by growth factors in cell culture experiments. The rephosphorylation of cytidylyltransferase after an ol eate-mediated dephosphorylation and translocation to membranes was inc reased after 2 min in the presence of insulin or epidermal growth fact or by 99% and 76%, respectively, compared with controls. However, the increased phosphorylation of cytidylyltransferase did not have an effe ct on its subcellular distribution. Furthermore, purified cytidylyltra nsferase preincubated with alkaline phosphatase is a substrate for p44 (mapk), a member of the mitogen-activated protein (MAP) kinase family downstream of the growth factor receptors, in vitro. In accordance wit h the in vivo data, in vitro phosphorylation of cytidylyltransferase b y p44(mapk) occurred after 2 min.