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  • The EMBO Journal (1999) 18, 1223 - 1234
  • doi:10.1093/emboj/18.5.1223

Apoptosis inhibitory activity of cytoplasmic p21Cip1/WAF1 in monocytic differentiation

Minoru Asada1, Takayuki Yamada1, Hidenori Ichijo2,3, Domenico Delia4, Kohei Miyazono2, Kenji Fukumuro5,6 and Shuki Mizutani1

  1. Department of Virology, The National Children's Medical Research Center, 3-35-31, Taishido, Setagaya-ku, Tokyo, 154, Japan
  2. Department of Biochemistry, The Cancer Institute, Japanese Foundation for Cancer Research, 1-37-1 Kami-Ikebukuro, Toshima-ku, Tokyo, 170, Japan
  3. Department of Biomaterials Science, Faculty of Dentistry, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan
  4. Division of Experimental Oncology, Instituto Nazionale Tumori, Via G, Venezian 1, 20133 Milan, Italy
  5. Department of Pharmacotherapeutics, Tokyo Science University, 12 Funakawara-cho, Shinjuku-ku, Tokyo, 113-8549, Japan
  6. Present address: Division of Hospital Pharmacy, Tokyo Women's Medical College, 8-1 Kawada-cho, Shinjuku-ku, Tokyo, Japan

Correspondence to:

Shuki Mizutani, E-mail: smizutani@nch.go.jp

Received 29 June 1998; Accepted 5 January 1998; Revised 7 December 1998

p21Cip1/WAF1 inhibits cell-cycle progression by binding to G1 cyclin/CDK complexes and proliferating cell nuclear antigen (PCNA) through its N- and C-terminal domains, respectively. The cell-cycle inhibitory activity of p21Cip1/WAF1 is correlated with its nuclear localization. Here, we report a novel cytoplasmic localization of p21Cip1/WAF1 in peripheral blood monocytes (PBMs) and in U937 cells undergoing monocytic differentiation by in vitro treatment with vitamin D3 or ectopic expression of p21Cip1/WAF1, and analyze the biological consequences of this cytoplasmic expression. U937 cells which exhibit nuclear p21Cip1/WAF1 demonstrated G1 cell-cycle arrest and subsequently differentiated into monocytes. The latter event was associated with a cytoplasmic expression of nuclear p21Cip1/WAF1, concomitantly with a resistance to various apoptogenic stimuli. Biochemical analysis showed that cytoplasmic p21Cip1/WAF1 forms a complex with the apoptosis signal-regulating kinase 1 (ASK1) and inhibits stress-activated MAP kinase cascade. Expression of a deletion mutant of p21Cip1/WAF1 lacking the nuclear localization signal (DeltaNLS-p21) did not induce cell cycle arrest nor monocytic differentiation, but led to an apoptosis-resistant phenotype, mediated by binding to and inhibition of the stress-activated ASK1 activity. Thus, cytoplasmic p21Cip1/WAF1 itself acted as an inhibitor of apoptosis. Our findings highlight the different functional roles of p21Cip1/WAF1, which are determined by its intracellular distribution and are dependent on the stage of differentiation.

  • Keywords:

    • apoptosis,
    • cell differentiation,
    • cytoplasmic p21,
    • nuclear p21