Relief from Contact Inhibition

The viral transformation of normal into tumorigenic cells is a system under active investigation . The fact that transformation is accompanied by loss of contact-inhibition has focused attention on other situations in which confluent cells can be caused to resume movement and cell division . One such system is the serum-stimulated relief of contact-inhibition in cultured fibroblasts (1, 2, 3) . Since an alteration of shape by "rounding-up" precedes movement (4), an investigation of biochemical changes known to accompany other alterations in the cell surface is pertinent . Phospholipid turnover, which appears to increase during such processes as phagocytosis (5, 6, 7, 8), secretion (9, 10) or the phytohaemagglutinin-mediated activation of lymphocytes (11, 12, 13), was accordingly examined. By using fibroblasts prelabeled with isotope, uncertainties of interpretation resulting from fluctuations in precursor pools (14, 15, 16) have been avoided .