TTK/hMPS1 is an attractive therapeutic target for triple-negative breast cancer.

Virginie Maire,Stéphane Depil,Thierry Dubois,Sergio Roman-Roman,Anne Vincent-Salomon,Leanne De Koning,Marion Richardson,Aurélie Dumont,Emmanuel Barillot,Eléonore Gravier,Francisco Cruzalegui,Bérengère Marty-Prouvost,Bruno Tesson,David Gentien,Guillem Rigaill,Alain Pierré,Céline Baldeyron,Gordon C Tucker

doi:10.1371/journal.pone.0063712

Abstract

Triple-negative breast cancer (TNBC) represents a subgroup of breast cancers (BC) associated with the most aggressive clinical behavior. No targeted therapy is currently available for the treatment of patients with TNBC. In order to discover potential therapeutic targets, we searched for protein kinases that are overexpressed in human TNBC biopsies and whose silencing in TNBC cell lines causes cell death. A cohort including human BC biopsies obtained at Institut Curie as well as normal tissues has been analyzed at a gene-expression level. The data revealed that the human protein kinase monopolar spindle 1 (hMPS1), also known as TTK and involved in mitotic checkpoint, is specifically overexpressed in TNBC, compared to the other BC subgroups and healthy tissues. We confirmed by immunohistochemistry and reverse phase protein array that TNBC expressed higher levels of TTK protein compared to the other BC subgroups. We then determined the biological effects of TTK depletion by RNA interference, through analyses of tumorigenic capacity and cell viability in different human TNBC cell lines. We found that RNAi-mediated depletion of TTK in various TNBC cell lines severely compromised their viability and their ability to form colonies in an anchorage-independent manner. Moreover, we observed that TTK silencing led to an increase in H2AX phosphorylation, activation of caspases 3/7, sub-G1 cell population accumulation and high annexin V staining, as well as to a decrease in G1 phase cell population and an increased aneuploidy. Altogether, these data indicate that TTK depletion in TNBC cells induces apoptosis. These results point out TTK as a protein kinase overexpressed in TNBC that may represent an attractive therapeutic target specifically for this poor prognosis associated subgroup of breast cancer.

Highlights

Breast cancer (BC) is one of the most common human malignancies, accounting for 22% of all cancers diagnosed in women
From gene expression analyses performed on a cohort of normal breast tissues and human BC biopsies obtained from Institut Curie, where all BC subtypes are almost represented, we found that RNA transcript levels of the human protein kinase monopolar spindle 1 gene, which encodes a dual serine/threonine kinase involved in the mitotic spindle assembly checkpoint (SAC) [17,18], are highly increased in Triple-negative breast cancer (TNBC) samples compared to the other BC subgroups and normal tissue samples
We confirmed by microarray-based transcriptional profiling analyses that the breast cancer subtypes identified by IHC clustered according to BLBC/TNBC, human epidermal growth factor receptor 2-overexpressing (Her2), LA and LB breast cancer gene-expression signatures [39]

Summary

Introduction

Breast cancer (BC) is one of the most common human malignancies, accounting for 22% of all cancers diagnosed in women. Global gene-expression analyses have revealed four main distinct subgroups in human breast tumors: luminal A and luminal B (LA and LB), human epidermal growth factor receptor 2-overexpressing (Her2) and basal-like (BLBC) breast cancers [1,2,3,4]. LA and LB express hormone receptor-related genes, estrogen receptor (ER) and progesterone receptor (PR). BLBC (and triple-negative breast cancers (TNBC)) are characterized by the absence of ER and PR expression and the lack of Her overexpression [5]. BLBC are positive for the expression of basal cytokeratins (CK5/ 6, CK14) and/or epidermal growth factor receptor (EGFR) [6,7,8]

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Results

Conclusion