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Expression of the Catalytic and Regulatory Subunits of Protein Phosphatase Type 2A May Be Differentially Modulated during Retinoic Acid-induced Granulocytic Differentiation of HL-60 Cells¹

The 2nd Department of Internal Medicine, Mie University School of Medicine, Edobashi, Tsu, Mie 514 Japan [M. N., S. B. O., H. T., I. T., K. D.]; Carcinogenesis Division, National Cancer Center Research Institute, Chuo-ku, Tokyo, 104 Japan [H. S., M. N.]; Friedrich Miescher-Institut, CH-4002, Basel, Switzerland [B. A. H.]; and Department of Pharmacology, University of Texas, Southwestern Medical Center, Dallas, Texas 75235-9041 [M. C. M.]

To elucidate the regulation of protein phosphatases types 1 (PP1) and 2A (PP2A) during all-trans retinoic acid (ATRA)-induced granulocytic differentiation of HL-60 cells, the phosphatase activity, proteins, and gene expressions of PP1 and PP2A were examined. Treatment with 1 µM ATRA caused an 85% decrease in the PP2A activity in extracts from HL-60 cells, while the PP1 activity was constant. This reduction in PP2A activity appeared to parallel phenotypic and functional changes of HL-60 cells induced by ATRA. Western blot analysis showed that the level of PP2A catalytic subunit (PP2A-C) decreased during the course of ATRA-induced differentiation, whereas expressions of A and B (M_r 55,000) regulatory subunits of PP2A were relatively unaltered. Expressions of PP1 catalytic subunit isozymes (PP1, PP1, and PP1) were not significantly affected by ATRA treatment. Northern blot analysis revealed that mRNA levels of PP2A-Cß and A regulatory subunits were decreased following treatment with ATRA, while levels of PP2A-C and B (M_r 55,000) regulatory subunit transcripts were relatively constant. Selective down regulation of PP2A-Cß preceded the granulocytic maturation induced by ATRA. Expressions of PP2A-C isoforms and A and B regulatory subunits may be differentially modulated during ATRA-induced granulocytic differentiation of HL-60 cells.

¹ This work was supported in part by grants for research from The Ministry of Education, Science, and Culture, Japan.

² To whom requests for reprints should be addressed.

Received 3/16/94. Accepted 7/11/94.

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