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Molecular and Cellular Biology, August 2000, p. 6159-6169, Vol. 20, No. 16
Department of Microbiology and Immunology,
Kimmel Cancer Center, Thomas Jefferson University, Philadelphia,
Pennsylvania 19107,1 and Department of
Biomedical Sciences, Section of General Pathology, University of
Modena, Modena, Italy2
Received 20 January 2000/Returned for modification 17 March
2000/Accepted 8 May 2000
The DNA binding activity of FUS (also known as TLS), a nuclear
pro-oncogene involved in multiple translocations, is regulated by
BCR-ABL in a protein kinase C
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
BCR-ABL Prevents c-Jun-Mediated and Proteasome-Dependent FUS
(TLS) Proteolysis through a Protein Kinase C
II-Dependent
Pathway
II (PKC
II)-dependent manner. We show
here that in normal myeloid progenitor cells FUS, although not visibly
ubiquitinated, undergoes proteasome-dependent degradation, whereas in
BCR-ABL-expressing cells, degradation is suppressed by PKC
II
phosphorylation. Replacement of serine 256 with the phosphomimetic
aspartic acid prevents proteasome-dependent proteolysis of FUS, while
the serine-256-to-alanine FUS mutant is unstable and susceptible to
degradation. Ectopic expression of the phosphomimetic S256D FUS mutant
in granulocyte colony-stimulating factor-treated 32Dcl3 cells induces
massive apoptosis and inhibits the differentiation of the cells
escaping cell death, while the degradation-prone S256A mutant has no
effect on either survival or differentiation. FUS proteolysis is
induced by c-Jun, is suppressed by BCR-ABL or Jun kinase 1, and
does not depend on c-Jun transactivation potential, ubiquitination, or
its interaction with Jun kinase 1. In addition, c-Jun-induced FUS
proteasome-dependent degradation is enhanced by heterogeneous nuclear
ribonucleoprotein (hnRNP) A1 and depends on the formation of a
FUS-Jun-hnRNP A1-containing complex and on lack of PKC
II
phosphorylation at serine 256 but not on FUS ubiquitination. Thus,
novel mechanisms appear to be involved in the degradation of FUS in
normal myeloid cells; moreover, the ability of the BCR-ABL oncoprotein
to suppress FUS degradation by the induction of posttranslational
modifications might contribute to the phenotype of BCR-ABL-expressing
hematopoietic cells.
*
Corresponding author. Mailing address for Danilo
Perrotti: Department of Microbiology and Immunology, Kimmel Cancer
Center, Thomas Jefferson University, BLSB 630, 233 S. 10th St.,
Philadelphia, PA 19107. Phone: (215) 503-4523. Fax: (215) 923-0249. E-mail: Danilo.Perrotti{at}mail.tju.edu. Mailing address
for Bruno Calabretta: Department of Microbiology and Immunology, Kimmel
Cancer Center, Thomas Jefferson University, BLSB 630, 233 S. 10th
St., Philadelphia, PA 19107. Phone: (215) 503-4522. Fax: (215)
923-0249. E-mail: Bruno.Calabretta{at}mail.tju.edu.
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