Ras-related GTP-binding proteins and leukocyte signal transduction.

Many aspects of leukocyte function are regulated by both heterotrimeric and Ras-related GTP-binding proteins, but there is little definite information about their roles in the specialized processes utilized by leukocytes for cell killing. Recent progress in understanding the regulation of the phagocyte NADPH oxidase by the Rac GTP-binding proteins provides a basis for defining the operational characteristics of one such phagocyte system. It is clear from various studies that the activity of the NADPH oxidase can be modulated through the regulation of the GTP-GDP state of Rac. Proteins exist in leukocytes able to modify GTP-binding protein function in this manner, and their activity may be regulated by signals generated on phagocyte stimulation. Proteins of the Ras superfamily are likely to be involved in a variety of normal phagocyte functions through their ability to modulate the assembly of actin filaments, direct vesicle trafficking and fusion, and so forth.