Neuraminidase stimulates Division and Sugar Uptake in Density-inhibited Cell Cultures

THE proliferation of normal cells stops when the cultures have formed confluent monolayers; this process is termed density-dependent inhibition of growth (DDI). The cells can be released from DDI by proteolytic enzymes and other substances acting on the cell surface¹, indicating that the cell surface may be important in regulating cell proliferation. Sialic acid residues also may be important in this regulation. Growing and virus-transformed cells contain less sialic acid in glycolipids² and possibly also in glycoproteins³ than normal resting cells. We report direct evidence that the control of cell growth is related to sialic acid residues on the cell surface. Small concentrations of neuraminidase initiate proliferation in stationary cell cultures and cause an early increase in sugar uptake.