Alkalinization of the lysosomes is correlated with ras transformation of murine and human fibroblasts.

The pH of the intralysosomal compartment of fibroblasts in culture was monitored by measuring the fluorescence emission intensity at 530 nm of fluid phase pinocytosed fluorescein-conjugated dextrans (FITC-dextrans) excited at 488 and 457 nm. Following the procedure of Ohkuma and Poole (Ohkuma, S., and Poole, B. (1978) Proc. Natl. Acad. Sci. U. S. A. (1978) 75, 3327-3331), a relationship was established between the fluorescence emission intensity of the FITC-dextrans and pH. This correlation was used to determine the intralysosomal apparent pH (pHapp) of a series of fibroblast cultures. The mean intralysosomal pHapp values of nontransformed mouse 3T3 fibroblasts and an infinite life-span human fibroblast cell strain, designated MSU-1.1, was 5.0. In distinction that of 3T3 fibroblasts transformed to the malignant state by Kirsten murine sarcoma virus and MSU-1.1 cells transformed by transfection of the v-Ki-ras or T24 H-ras oncogene was 6.1. These measurements suggest that ras transformation results in a significant perturbation of lysosomal pH.