Autophagocytosis in serum and amino acid starved HeLa cells

Autophagocytosis occurs to some extent in normal cells, and its rate increases in many pathologic conditions such as a sublethal reaction to injury. Autophagy has been observed in tissue culture cells in response to chloroquine, iron toxicity, and increased pH, but a reproducible physiologic model has not been developed. Because in vivo studies have shown that starvation causes autophagy in rat liver cells, the effect of specific nutritional deprivation of serum and amino acids was studied in HeLa cells. Morphologic alterations were studied by electron microscopy, phase contrast microscopy, cinemicrography, and ultrastructural cytochemistry following removal of all amino acids and serum from the medium. Cells were fixed either in glutaraldehyde or in a 'cocktail' of glutaraldehyde and osmium tetroxide. Acid phosphatase was demonstrated with a modified Gomori method. Autophagic vacuoles were rarely seen in HeLa cells maintained in log phase by frequent subdivision, but small primary lysosomes, multivesicular bodies and residual bodies were present. Early changes in cells exposed to deficient medium included an increased number of autophagic vacuoles and larger, more numerous acid phosphatase positive primary and secondary lysosomes. Later changes included an increase in number and size of acid phosphatase positive autophagic vacuoles, more lysosomes containing loosely packed membranous debris, and degenerative changes in other organelles. These findings indicate that serum and amino acid deprivation in HeLa cells provides a useful model for study of cellular autophagocytosis.