Isolation and characteristics of HeLa surface proteins

HeLa 71 and 65 cells grown in attached culture possess a coat of extracellular proteins that can be released from the cell by mild EDTA-detachment, with no significant effect on cellular integrity. This suggests that these surface proteins are weakly associated with the cell, possibly through divalent cations. The high affinity of surface proteins for critical divalent cations, shown by their high precipitability by Zn²⁺, Ca²⁺ and Mg²⁺, supports this assumption. Since surface proteins appear to be phosphoproteins, as suggested by significant incorporation of ³²Pi in vitro, it is possible that binding occurs through The amount of surface protein on HeLa 65 cells grown in suspension culture is greatly reduced compared with cells grown in monolayer culture. This may be related to impaired availability of Ca²⁺ in suspension culture medium. In monolayer grown HeLa cells surface proteins are predominantly distributed underneath the cells. The highest amount of these proteins is found on cells prior to growth initiation and steadily decreases as cells approach confluency. As shown by radioactive leucine protein labeling, surface proteins are primarily comprised of proteins synthesized within HeLa cells and released to the outer cell surface. The presence of serum proteins in surface protein matrix is physiologically significant.