Ethnic and racial-specific differences in levels of centrosome-associated mitotic kinases, proliferative and epithelial-to-mesenchymal markers in breast cancers

Abstract

Molecular epidemiology evidence indicates racial and ethnic differences in the aggressiveness and survival of breast cancer. Hispanics/Latinas (H/Ls) and non-Hispanic Black women (NHB) are at higher risk of breast cancer (BC)-related death relative to non-Hispanic white (NHW) women in part because they are diagnosed with hormone receptor-negative (HR) subtype and at higher stages. Since the cell cycle is one of the most commonly deregulated cellular processes in cancer, we propose that the mitotic kinases TTK (or Mps1), TBK1, and Nek2 could be novel targets to prevent breast cancer progression among NHBs and H/Ls. In this study, we calculated levels of TTK, p-TBK1, epithelial (E-cadherin), mesenchymal (Vimentin), and proliferation (Ki67) markers through immunohistochemical (IHC) staining of breast cancer tissue microarrays (TMAs) that includes samples from 6 regions in the Southeast of the United States and Puerto Rico -regions enriched with NHB and H/L breast cancer patients. IHC analysis showed that TTK, Ki67, and Vimentin were significantly expressed in triple-negative (TNBC) tumors relative to other subtypes, while E-cadherin showed decreased expression. TTK correlated with all of the clinical variables but p-TBK1 did not correlate with any of them. TCGA analysis revealed that the mRNA levels of multiple mitotic kinases, including TTK, Nek2, Plk1, Bub1, and Aurora kinases A and B, and transcription factors that are known to control the expression of these kinases (e.g. FoxM1 and E2F1-3) were upregulated in NHBs versus NHWs and correlated with higher aneuploidy indexes in NHB, suggesting that these mitotic kinases may be future novel targets for breast cancer treatment in NHB women.

Keywords: Breast cancer; E-cadherin; Ki67; Nek2; TBK1; TTK; Tissue microarray; Vimentin.

Fig. 1

TBK1 and TTK are overexpressed in different breast cancer subtypes. METABRIC (RNA seq Z values) analysis of mRNA expression of TBK1 and TTK by breast cancer molecular subtype classification. cBioPortal analyses of mRNA expression of TBK1 and TTK mitotic kinases in lobular and ductal breast cancer subtypes determined by PAM50 molecular subtyping, n = 2509. A z-score threshold ± 2.0 was used for optimal results. Significance was addressed with ANOVA

Fig. 2

The mRNA expression of mitotic kinases in different racial and ethnic groups. Expression patterns of Nek2, TTK, and TBK1 in breast cancer patients from TCGA (A–C). A z-score threshold ± 2.0 was used for optimal results. P-values were calculated using a pairwise ANOVA t-test and a Dunn analysis for the Kruskal–Wallis Test. The results for the three kinases resulted in P < 2.96e-06 to 7.3e-08 (***). Expression of Nek2, TTK, and TBK1 as a function of ancestry. P-values were calculated using the Kruskal–Wallis Test.

Fig. 3

A breast cancer tissue microarray showing TTK correlates with EMT and proliferation biomarkers in different breast cancer pathological subtypes. A. Representative IHC images using several surrogate markers of breast cancer (40X). The scale = 50 microns. Mean Allred scores of the indicated proteins related to pathological subtypes B. p-TBK1 levels were assessed in TNBC patients from the USA. P-values were derived from the Kruskal–Wallis Test