PRKCQ inhibition enhances chemosensitivity of triple-negative breast cancer by regulating Bim

Jessica H Byerly,Hanna Y Irie,Elisa R Port

doi:10.1186/s13058-020-01302-w

Abstract

BackgroundProtein kinase C theta, (PRKCQ/PKCθ) is a serine/threonine kinase that is highly expressed in a subset of triple-negative breast cancers (TNBC) and promotes their growth, anoikis resistance, epithelial-mesenchymal transition (EMT), and invasion. Here, we show that PRKCQ regulates the sensitivity of TNBC cells to apoptosis triggered by standard-of-care chemotherapy by regulating levels of pro-apoptotic Bim.MethodsTo determine the effects of PRKCQ expression on chemotherapy-induced apoptosis, shRNA and cDNA vectors were used to modulate the PRKCQ expression in MCF-10A breast epithelial cells or triple-negative breast cancer cells (MDA-MB231Luc, HCC1806). A novel PRKCQ small-molecule inhibitor, 17k, was used to inhibit kinase activity. Viability and apoptosis of cells treated with PRKCQ cDNA/shRNA/inhibitor +/-chemotherapy were measured. Expression levels of Bcl2 family members were assessed.ResultsEnhanced expression of PRKCQ is sufficient to suppress apoptosis triggered by paclitaxel or doxorubicin treatment. Downregulation of PRKCQ also enhanced the apoptosis of chemotherapy-treated TNBC cells. Regulation of chemotherapy sensitivity by PRKCQ mechanistically occurs via regulation of levels of Bim, a pro-apoptotic Bcl2 family member; suppression of Bim prevents the enhanced apoptosis observed with combined PRKCQ downregulation and chemotherapy treatment. Regulation of Bim and chemotherapy sensitivity is significantly dependent on PRKCQ kinase activity; overexpression of a catalytically inactive PRKCQ does not suppress Bim or chemotherapy-associated apoptosis. Furthermore, PRKCQ kinase inhibitor treatment suppressed growth, increased anoikis and Bim expression, and enhanced apoptosis of chemotherapy-treated TNBC cells, phenocopying the effects of PRKCQ downregulation.ConclusionsThese studies support PRKCQ inhibition as an attractive therapeutic strategy and complement to chemotherapy to inhibit the growth and survival of TNBC cells.

Highlights

Protein kinase C theta, (PRKCQ/PKCθ) is a serine/threonine kinase that is highly expressed in a subset of triple-negative breast cancers (TNBC) and promotes their growth, anoikis resistance, epithelial-mesenchymal transition (EMT), and invasion
PRKCQ overexpression is sufficient to enhance the viability of these cells in the presence of chemotherapeutic agents commonly used in the treatment of patient triple-negative breast cancers, such as doxorubicin and paclitaxel (Fig. 1a, b)
The suppression of chemotherapy-induced apoptosis by PRKCQ is dependent on the catalytic activity of PRKCQ, as overexpression of kinase-inactive PRKCQ failed to suppress apoptosis in paclitaxel or doxorubicintreated cells (Fig. 1c–f)

Summary

Introduction

Protein kinase C theta, (PRKCQ/PKCθ) is a serine/threonine kinase that is highly expressed in a subset of triple-negative breast cancers (TNBC) and promotes their growth, anoikis resistance, epithelial-mesenchymal transition (EMT), and invasion. We show that PRKCQ regulates the sensitivity of TNBC cells to apoptosis triggered by standard-of-care chemotherapy by regulating levels of pro-apoptotic Bim. Triple-negative breast cancer (TNBC) represents approximately 15% of all diagnosed breast cancer cases. Many patients do well with standard-of-care chemotherapy, some TNBCs have incomplete responses leading to metastatic recurrences that are associated with significant morbidity and mortality. New therapeutic strategies that suppress the growth and spread of TNBC cells could improve outcomes and quality of life for patients. PRKCQ/PKCθ is a serine/threonine kinase that is a member of the novel PKC family (reviewed in [3, 4]). PRKCQ maps to chromosome 10p15, a region frequently mutated in T cell leukemia, lymphomas, and T cell immunodeficiencies [3]

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Discussion

Conclusion