MELK expression correlates with tumor mitotic activity but is not required for cancer growth

Abstract

The Maternal Embryonic Leucine Zipper Kinase (MELK) has been identified as a promising therapeutic target in multiple cancer types. MELK over-expression is associated with aggressive disease, and MELK has been implicated in numerous cancer-related processes, including chemotherapy resistance, stem cell renewal, and tumor growth. Previously, we established that triple-negative breast cancer cell lines harboring CRISPR/Cas9-induced null mutations in MELK proliferate at wild-type levels in vitro (Lin et al., 2017). Here, we generate several additional knockout clones of MELK and demonstrate that across cancer types, cells lacking MELK exhibit wild-type growth in vitro, under environmental stress, in the presence of cytotoxic chemotherapies, and in vivo. By combining our MELK-knockout clones with a recently described, highly specific MELK inhibitor, we further demonstrate that the acute inhibition of MELK results in no specific anti-proliferative phenotype. Analysis of gene expression data from cohorts of cancer patients identifies MELK expression as a correlate of tumor mitotic activity, explaining its association with poor clinical prognosis. In total, our results demonstrate the power of CRISPR/Cas9-based genetic approaches to investigate cancer drug targets, and call into question the rationale for treating patients with anti-MELK monotherapies.

Inhibition of MELK produces potential anti‐tumour effects in bladder cancer by inducing G1/S cell cycle arrest via the ATM/CHK2/p53 pathway

“…In addition, in accordance with bioinformatics analyses of GSE13507, MELK was involved in the cell cycle, G1/S transition of the mitotic cell cycle, DNA repair and replication, which was similar to previous reports 6,26,33,[39][40][41][42][43]. A, The expression of MELK was up-regulated at transcription level with MELK plasmid; it was down-regulated by OTSSP167.…”

Maternal embryonic leucine zipper kinase: A novel biomarker and a potential therapeutic target of cervical cancer

“…27 Kohler et al 14 found that the use of MELK inhibitor OTSSP167 can induce G2/M cell cycle arrest, inhibit proliferation and colony formation, and induce apoptosis of HGSOC cell lines. Another two studies reported that MELK expression is associated with tumor cell mitosis 28 and promotes tumor cell proliferation. 29 MELK also plays an important role in the P53-P21 apoptotic pathway.…”

Generating Single Cell–Derived Knockout Clones in Mammalian Cells with CRISPR/Cas9

“…experiments to confirm knockout of the MELK kinase from cancer cell lines (Giuliano, Lin, Smith, Palladino, & Sheltzer, 2018;Lin, Giuliano, Sayles, & Sheltzer, 2017).…”

“…Rederiving a cell line from a single cell represents a significant genetic bottleneck, and experiments may be confounded if a single cellderived clone captures only a subset of the diversity present within the starting cell population. Indeed, some established cell lines are well known to exhibit significant interclonal heterogeneity; for instance, we and others have observed sizeable variation in proliferative capacity among clones derived from the widely used MDA-MB-231 breast cancer cell line (Giuliano et al, 2018;Khan, Kim, Shin, & Lee, 2017;Lin et al, 2017). Because of the possibility of parental heterogeneity, it is absolutely crucial that researchers analyze multiple independent knockout cell lines in order to ensure that any unexpected result is not a clonal artifact.…”