Proteoglycans are found in all animal cells. One class of proteoglycans is defined by its location at the cell surface. The cell surface proteoglycans bind cells to the extracellular matrix, organize the cytoskeleton, and act as receptors for a variety of ligands. There are two major populations of cell surface proteoglycans, based upon the interaction of the molecules with the plasma membrane. Peripheral membrane proteoglycans are bound to putative receptors on the cell membrane through electrostatic interactions. Integral membrane proteoglycans contain a hydrophobic core protein or lipid anchor which embeds the molecule in the plasma membrane. Within the peripheral and integral membrane proteoglycan populations are classes of proteoglycans, based upon the structure of the glycosaminoglycan chains or the protein core, or the type of membrane anchor. Cell surface proteoglycans are shed from a variety of cultured cells. It is thought that this shedding may play a role in cell division and growth, by disrupting interactions of cells with the extracellular matrix or cytoskeleton. Chinese hamster ovary (CHO) cells have cell surface proteoglycans which appear to be shed into the media. Very little is known about the populations, structures and metabolism of the proteoglycans on the cell surface, although evidence from a proteoglycan synthesis mutant, pgsE-606, suggests that there are populations of heparan sulfate proteoglycans in CHO cells. We propose to characterize the populations of cell surface proteoglycans on wild-type and pgsE-606 CHO cells. The proportion of peripheral and integral membrane proteoglycans on the cell surface will be determined, and the structures of each proteoglycan population will be analyzed. We will determine if there are classes of peripheral and integral membrane proteoglycans by treating the cells with different agents to displace the molecules from the cell surface, measuring the affinities of proteoglycans for hydrophobic resins, and analyzing the structure of the membrane anchor(s). Kinetic studies of the cell surface proteoglycans will be performed to determine if the peripheral and integral proteoglycans are metabolically related. Once the cell surface proteoglycans are characterized we will be able to devise strategies to isolate CHO mutants defective in shedding of the cell surface molecules. These turnover mutants will complement the mutants we have isolated that are defective in the intracellular degradation of proteoglycans.
| Bame, K J (1993) Release of heparan sulfate glycosaminoglycans from proteoglycans in Chinese hamster ovary cells does not require proteolysis of the core protein. J Biol Chem 268:19956-64 |
