Insights into a plasma membrane signature

The plasma membrane (PM) is an organized biological system that serves as a structural barrier and communication interface with the extracellular envi ronment. Many basic questions regarding the PM as a system remain unanswere d. In particular, we do not understand the scope of similarity and differen ces in protein expression at the PM. This study takes an initial step towar d addressing these questions by comparing the PM proteomes of fibroblasts a nd mammary carcinoma cells. Three sets of proteins were revealed by the stu dy. The first set comprises between 9 and 23% of all proteins at the PM and appears to be common to both fibroblasts and mammary carcinoma. A second g roup of proteins, comprising similar to 40% of the proteins at the PM, is t ightly linked to cell lineage. The third set of proteins is unique to each cell line and is independent of cell lineage. It is reasonable to hypothesi ze then, that this third group of proteins is responsible for unique aspect s of cell behavior. In an effort to find proteins linked to the metastatic phenotype, we identified several proteins that are uniquely expressed at th e PM of the metastatic MDA-MB-435 cells. These proteins have functions rang ing from cell adhesion to the regulation of translation and the control of oxidant stress.