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Interferon-?-induced upregulation of immunoproteasome subunit assembly overcomes bortezomib resistance in human hematological cell lines.

ABSTRACT:

Background

Despite encouraging results with the proteasome inhibitor bortezomib in the treatment of hematologic malignancies, emergence of resistance can limit its efficacy, hence calling for novel strategies to overcome bortezomib-resistance. We previously showed that bortezomib-resistant human leukemia cell lines expressed significantly lower levels of immunoproteasome at the expense of constitutive proteasomes, which harbored point mutations in exon 2 of the PSMB5 gene encoding the ?5 subunit. Here we investigated whether up-regulation of immunoproteasomes by exposure to interferon-? restores sensitivity to bortezomib in myeloma and leukemia cell lines with acquired resistance to bortezomib.

Methods

RPMI-8226 myeloma, THP1 monocytic/macrophage and CCRF-CEM (T) parental cells and sub lines with acquired resistance to bortezomib were exposed to Interferon-? for 24-48 h where after the effects on proteasome subunit expression and activity were measured, next to sensitivity measurements to proteasome inhibitors bortezomib, carfilzomib, and the immunoproteasome selective inhibitor ONX 0914. At last, siRNA knockdown experiments of ?5i and ?1i were performed to identify the contribution of these subunits to sensitivity to proteasome inhibition. Statistical significance of the differences were determined using the Mann-Whitney U test.

Results

Interferon-? exposure markedly increased immunoproteasome subunit mRNA to a significantly higher level in bortezomib-resistant cells (up to 30-fold, 10-fold, and 6-fold, in ?1i, ?5i, and ?2i, respectively) than in parental cells. These increases were paralleled by elevated immunoproteasome protein levels and catalytic activity, as well as HLA class-I. Moreover, interferon-? exposure reinforced sensitization of bortezomib-resistant tumor cells to bortezomib and carfilzomib, but most prominently to ONX 0914, as confirmed by cell growth inhibition studies, proteasome inhibitor-induced apoptosis, activation of PARP cleavage and accumulation of polyubiquitinated proteins. This sensitization was abrogated by siRNA silencing of ?5i but not by ?1i silencing, prior to pulse exposure to interferon-?.

Conclusion

Downregulation of ?5i subunit expression is a major determinant in acquisition of bortezomib-resistance and enhancement of its proteasomal assembly after induction by interferon-? facilitates restoration of sensitivity in bortezomib-resistant leukemia cells towards bortezomib and next generation (immuno) proteasome inhibitors.

SUBMITTER: Niewerth D

PROVIDER: S-EPMC3896789 | biostudies-literature | 2014 Jan

REPOSITORIES: biostudies-literature

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Publications

Interferon-γ-induced upregulation of immunoproteasome subunit assembly overcomes bortezomib resistance in human hematological cell lines.

Niewerth Denise D Kaspers Gertjan J L GJ Assaraf Yehuda G YG van Meerloo Johan J Kirk Christopher J CJ Anderl Janet J Blank Jonathan L JL van de Ven Peter M PM Zweegman Sonja S Jansen Gerrit G Cloos Jacqueline J

Journal of hematology & oncology 20140113

<h4>Background</h4>Despite encouraging results with the proteasome inhibitor bortezomib in the treatment of hematologic malignancies, emergence of resistance can limit its efficacy, hence calling for novel strategies to overcome bortezomib-resistance. We previously showed that bortezomib-resistant human leukemia cell lines expressed significantly lower levels of immunoproteasome at the expense of constitutive proteasomes, which harbored point mutations in exon 2 of the PSMB5 gene encoding the β5 ...[more]

PMID: 24418325

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