N-Ras induces alterations in Golgi complex architecture and in constitutive protein transport

Aberrant glycosylation of proteins and lipids is a common feature of many t umor cell types, and is often accompanied by alterations in membrane traffi c and an anomalous localization of Golgi-resident proteins and glycans. The se observations suggest that the Golgi complex is a key organelle for at le ast some of the functional changes associated with malignant transformation . To gain insight into this possibility, we have analyzed changes in the st ructure and function of the Golgi complex induced by the conditional expres sion of the transforming N-Ras(K61) mutant in the NRK cell line. A remarkab le and specific effect associated with this N-Ras-induced transformation wa s a conspicuous rearrangement of the Golgi complex into a collapsed morphol ogy, Ultrastructural and stereological analyses demonstrated that the Golgi complex was extensively fragmented. The collapse of the Golgi complex was also accompanied by a disruption of the actin cytoskeleton, Functionally, N -Ras-transformed KT8 cells showed an increase in the constitutive protein t ransport from the trans-Golgi network to the cell surface, and did not indu ce the appearance of aberrant cell surface glycans, The Golgi complex colla pse, the actin disassembly, and the increased constitutive secretion were a ll partially inhibited by the phospholipase A(2) inhibitor 4-bromophenylacy l bromide. The results thus suggest the involvement of the actin cytoskelet on in the shape of the Golgi complex, and intracellular phospholipase A(2) in its architecture and secretory function.