Studies on the plasma membrane proteins of normal and tumour cells

Abstract

The plasma membrane which forms the outer boundary of mammalian newlinecells is the interphase between the cell and its environment. It is more newlinethan just a barrier delimiting the cellular contents in that it participates newlinein many regulatory processes. The proteins situated in the plasma mem- newlinebrane receive signals from outside, and the signals in turn are transmitted newlineto the interior of cell, sometimes after amplification. They also regulate newlineactive transport across the membrane. In addition, cell-cell contact and newlinecontact of the cells with the substratum are mediated by the components newlineof the plasma membrane . There are perceptible differences at the level newlineof plasma membrane between the normal and cancer cells also. One such newlinemajor difference is the glycosylation level of proteins is normal cells newlineand tumour cells. In addition, protein products of many cellular oncogenes newlineare localized at the plasma membrane. Since many oncogene products newlineare believed to be involved in signal transduction, even from a causative newlinepoint of view the study of plasma membrane or the cell surface would newlineassume importance. newlineAmong the many processes that take place at the level of plasma newlinemembrane, phosphorylation is of prime importance because it is involved newlinein regulation of transmembrane-signal transduction. A majority of oncopro- newlineteins located in the plasma membrane are protein kinases. In addition newlineto these, there are products of oncogenes like ras which are believed newlineto be involved in the transduction of signals. There are similarities newlinebetween ras · gene products and G proteins in that they have guanine- newlinenucleotide-binding and GTPase activity. However, the precise biological newlinexvi newlinerole of ras proteins in any cellular process is far from clear. From newlinethis type of considerations there existed a theoretical possibility that newlineras proteins might modulate transduction of signals through phosphoryla- newlinetion. Therefore, the initial experiments were directed to check such newlinea possibility.