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BCR-ABL prevents c-jun-mediated and proteasome-dependent FUS (TLS) proteolysis through a protein kinase
D Perrotti1, A Iervolino, V Cesi
1Department of Microbiology and Immunology, Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Abstract:
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 CbetaII (PKCbetaII)-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 PKCbetaII 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 PKCbetaII 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.
Insights
The BCR-ABL oncoprotein suppresses FUS protein degradation in myeloid cells via PKCbetaII phosphorylation, preventing apoptosis and promoting cell survival. This regulation impacts hematopoietic cell phenotypes.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- FUS (also known as TLS) is a nuclear pro-oncogene implicated in various translocations.
- BCR-ABL, a tyrosine kinase, regulates FUS DNA binding activity through protein kinase CbetaII (PKCbetaII).
Purpose of the Study:
- To investigate the regulation of FUS degradation in myeloid progenitor cells.
- To elucidate the role of BCR-ABL and PKCbetaII in FUS proteolysis.
- To understand the impact of FUS degradation on cell survival and differentiation.
Main Methods:
- Analysis of FUS ubiquitination and proteasome-dependent degradation in normal and BCR-ABL-expressing myeloid cells.
- Site-directed mutagenesis of FUS at serine 256 (S256D phosphomimetic mutant and S256A mutant).
- Ectopic expression of FUS mutants in 32Dcl3 cells and assessment of apoptosis and differentiation.
Main Results:
- In normal myeloid cells, FUS undergoes proteasome-dependent degradation.
- BCR-ABL suppresses FUS degradation via PKCbetaII phosphorylation at serine 256.
- The S256D FUS mutant prevents degradation and induces apoptosis, while the S256A mutant is degraded and has no effect.
- c-Jun induces FUS degradation, which is enhanced by hnRNP A1, and suppressed by BCR-ABL or Jun kinase 1.
Conclusions:
- Novel mechanisms regulate FUS degradation in normal myeloid cells.
- BCR-ABL's suppression of FUS degradation through posttranslational modifications contributes to the phenotype of BCR-ABL-expressing hematopoietic cells.