posted on 2024-01-29, 07:40authored byXuemei Xie, Gaurav B. Chauhan, Ramakrishna Edupuganti, Takahiro Kogawa, Jihyun Park, Moises Tacam, Alex W. Tan, Mohd Mughees, Fnu Vidhu, Diane D. Liu, Juliana M. Taliaferro, Mary Kathryn Pitner, Luke S. Browning, Ju-Hyeon Lee, François Bertucci, Yu Shen, Jian Wang, Naoto T. Ueno, Savitri Krishnamurthy, Gabriel N. Hortobagyi, Debu Tripathy, Steven J. Van Laere, Geoffrey Bartholomeusz, Kevin N. Dalby, Chandra Bartholomeusz
Differential gene expression profile, consolidated gene set enrichment, and network analyses. A, Differences in gene expression are shown in volcano plot format, where the X-axis denotes the log2-transformed fold-change and the Y-axis denotes the –log10-transformed P value. The log2 fold-change was calculated as Cas9-p15 control cell fold-change/MELK KO MDA-MB-231 cell fold-change, resulting in positive values for genes overexpressed in the WT condition and negative values for genes overexpressed in the KO condition. The nominal P value threshold at 5% is indicated by a dashed blue horizontal line. The 10 most differentially expressed genes by P value are labeled using their gene symbol. B, Differences in the hallmark enrichment pattern are shown in a modified volcano plot format, where the X-axis denotes the normalized enrichment score and the Y-axis denotes the –log10-transformed P value. The normalized enrichment score was calculated as Cas9-p15 control cell score/MELK KO MDA-MB-231 cell score, resulting in positive values for hallmarks enriched in the WT condition and negative values for hallmarks enriched in the KO condition, as indicated at the top of the plot. The nominal P value threshold at 5% is indicated by a dashed blue horizontal line. Significant hallmarks are labeled using their gene set name. C, Pathway enrichment profile of the MELK-centered PPI network. In the left part of the plot, significantly enriched pathways, listed along the Y-axis, are represented in dot plot format; the X-axis represents the –log10-transformed P value; and the size of the dots reflects the number of pathway genes contained in the network. To the right of the dot plot, overlaps between enriched pathways and three gene sets defined after analyzing the MELK-centered protein–protein interaction network are indicated in heat map format. The gene sets of interest are indicated in the X-axis underneath the heat map, where dark blue denotes the presence of pathway genes and light blue denotes the absence of pathway genes in these gene sets.
UT | University of Texas MD Anderson Cancer Center (MD Anderson)
Cancer Prevention and Research Institute of Texas (CPRIT)
HHS | National Institutes of Health (NIH)
Triple-negative breast cancer (TNBC) has high relapse and metastasis rates and a high proportion of cancer stem-like cells (CSC), which possess self-renewal and tumor initiation capacity. MELK (maternal embryonic leucine zipper kinase), a protein kinase of the Snf1/AMPK kinase family, is known to promote CSC maintenance and malignant transformation. However, the role of MELK in TNBC metastasis is unknown; we sought to address this in the current study. We found that MELK mRNA levels were higher in TNBC tumors [8.11 (3.79–10.95)] than in HR+HER2− tumors [6.54 (2.90–9.26)]; P < 0.001]. In univariate analysis, patients with breast cancer with high-MELK–expressing tumors had worse overall survival (P < 0.001) and distant metastasis-free survival (P < 0.01) than patients with low-MELK–expressing tumors. In a multicovariate Cox regression model, high MELK expression was associated with shorter overall survival after adjusting for other baseline risk factors. MELK knockdown using siRNA or MELK inhibition using the MELK inhibitor MELK-In-17 significantly reduced invasiveness, reversed epithelial-to-mesenchymal transition, and reduced CSC self-renewal and maintenance in TNBC cells. Nude mice injected with CRISPR MELK-knockout MDA-MB-231 cells exhibited suppression of lung metastasis and improved overall survival compared with mice injected with control cells (P < 0.05). Furthermore, MELK-In-17 suppressed 4T1 tumor growth in syngeneic BALB/c mice (P < 0.001). Our findings indicate that MELK supports metastasis by promoting epithelial-to-mesenchymal transition and the CSC phenotype in TNBC.
These findings indicate that MELK is a driver of aggressiveness and metastasis in TNBC.