Effect of Trypsin on Cell Volume and Mass

Abstract

NORMAL cells stop growing in culture when they reach a certain saturation density^1–4 (contact inhibition of growth). The cells are arrested at the G₁ phase of the cell cycle, during which DNA synthesis is repressed and division does not occur^5,6. Whereas tumour cells are either less sensitive or insensitive to contact inhibition of growth⁴, normal cells can be rescued from this inhibition. Treatment with serum^1,7, cell derived factors⁸, low concentrations of proteolytic enzymes^8,9 and a number of other agents¹⁰ leads, after a certain time lag, to a resumption of DNA synthesis and mitosis. In conditions favourable for DNA synthesis and division, the size of a cell-whether normal or transformed-increases considerably¹¹, but only tumour cells form colonies¹². We now report that both normal and transformed cells immediately increase their volume and dry weight (mass) when exposed to a low dose of trypsin. This occurs when DNA synthesis is inhibited, and does not require new transcription; trypsin is therefore directly affecting the cell surface.