ALTERATIONS IN ACTIVITIES OF PROTEIN PHOSPHATASES PP1 AND PP2A IN T-LYMPHOCYTES AND B-LYMPHOCYTES OF AUTOIMMUNE MRL MPJ-LPR LPR MICE

Activities of protein phosphatases PP1 and PP2A were determined in T a nd B lymphocytes of autoimmune-prone MRL/MpJ-lpr/lpr mice (MRL/lpr mic e) and two control strains, MRL/MpJ-+/+ mice (MRL/+/+mice) and C3H/HeJ mice. Potential PP1 activity, which was measured after treatment of c ell extract with Co2+-trypsin, was much higher in T lymphocytes than B lymphocytes. However, no difference in the activity was observed betw een MRL/lpr mice and the controls. Spontaneous PP2A activity showed si milar levels in T and B lymphocytes from normal mice, but potential PP 2A activity, which was measured after treatment with 2-mercaptoethanol , was significantly higher in T lymphocytes from MRL/lpr mice than tho se from controls. No differences were detected in PP1 or PP2A activiti es in B lymphocytes. From these results, our previous data [Matsuzawa, S. et al. (1992) J. Biochem. 111, 472-477] demonstrating increases in potential activities of PP1 and PP2A in lymphoid tissues from autoimm une MRL/lpr mice can be interpreted as follows. 1) The increase in pot ential PP1 activity of the lymphoid tissues from MRL/lpr mice is cause d by replacement of B lymphocytes by abnormal T lymphocytes, which acc umulate in enormous numbers. 2) The increase of potential PP2A activit y in the lymphoid tissues from MRL/lpr mice is caused by the increase in this activity in their T lymphocytes.