Glyoxalase 1 (GLO1) is a ubiquitous enzyme involved in the detoxification of methylglyoxal, a cytotoxic byproduct of glycolysis that induces apoptosis. In this study, we found that GLO1 gene expression correlates with neoplasm histologic grade (χ2 test, p = 0.002) and is elevated in human basal-like breast cancer tissues. Approximately 90% of basal-like cancers were grade 3 tumors highly expressing both GLO1 and the cancer stem cell marker ALDH1A3. ALDH1high cells derived from the MDA-MB 157 and MDA-MB 468 human basal-like breast cancer cell lines showed elevated GLO1 activity. GLO1 inhibition using TLSC702 suppressed ALDH1high cell viability as well as the formation of tumor-spheres by ALDH1high cells. GLO1 knockdown using specific siRNAs also suppressed ALDH1high cell viability, and both TLSC702 and GLO1 siRNA induced apoptosis in ALDH1high cells. These results suggest GLO1 is essential for the survival of ALDH1-positive breast cancer stem cells. We therefore conclude that GLO1 is a potential therapeutic target for treatment of basal-like breast cancers.

c-Met is a receptor-type tyrosine kinase, which is involved in a wide range of cellular responses such as proliferation, motility, migration and invasion. It has been reported to be overexpressed in various cancers. However, the role of c-Met in breast cancer stem cells (CSCs) still remains unclear. We herein, show that c-Met expression is significantly elevated in Basal-like type of breast cancer in comparison with other subtypes. High expression of c-Met strongly correlated with the expression of two CSC markers, ALDH1A3 and CD133 in breast cancers. In addition, breast cancers at tumor stage III-IV expressing both c-Methigh and ALDH1A3high had poor prognosis. Furthermore, treatment with c-Met inhibitors (Crizotinib, Foretinib, PHA-665752 and Tivantinib) in MDA-MB157 cells with high c-Met protein expression resulted in significant suppression in cell viability, contrary to MDA-MB468 cells with low c-Met protein expression. These c-Met inhibitors also suppressed cell viability and tumor-sphere formation of ALDH1high breast cancer cells with high c-Met expression. These results suggest that c-Met in ALDH1 positive CSCs seems to play an important role in breast cancer repopulation. Therefore, we conclude that c-Met is a potential therapeutic target in ALDH1 positive breast CSCs.

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Only few orthologs of animal apoptosis regulators have been found in plants. Recently, the ectopic expression of mammalian inhibitor of apoptosis proteins (IAPs) has been shown to affect plant programmed cell death. Here, we identified two novel proteins homologous to Arabidopsis thaliana IAP-like protein (AtILP) 1 and 2 by applying an improved motif searching method. Furthermore, homologs of AtILP1 were found to occur as a novel gene family in other organisms such as fungi and animals including Homo sapiens (HsILP1). Like baculovirus IAP repeats (BIRs) in IAPs, ILPs contain two highly conserved BIR-like domains (BLDs) with a putative C2HC-type zinc finger. Phylogenetic analyses indicated that ILPs are putative paralogs of IAPs. Homology modeling revealed that the three-dimensional structure of BLD in HsILP1 is similar to that of BIR. Transient expression of HsILP1 resulted in inhibition of etoposide-induced apoptosis in HEK293 and HeLaS3 cells. These findings suggest that ILPs are conserved in a wide range of eukaryotes including plants, and that their functions are closely related to those of IAPs.