ABSTRACT
Despite development of markers for identification of cancer stem cells, the mechanism underlying the survival and division of cancer stem cells in breast cancer remains unclear. Here we report that PKCλ expression was enriched in basal-like breast cancer, among breast cancer subtypes, and was correlated with ALDH1A3 expression (p = 0.016, χ2-test). Late stage breast cancer patients expressing PKCλhigh and ALDH1A3high had poorer disease-specific survival than those expressing PKCλlow and ALDH1A3low (p = 0.018, log rank test for Kaplan-Meier survival curves: hazard ratio 2.58, 95% CI 1.24-5.37, p = 0.011, multivariate Cox regression analysis). Functional inhibition of PKCλ through siRNA-mediated knockdown or CRISPR-Cas9-mediated knockout in ALDH1high MDA-MB 157 and MDA-MB 468 basal-like breast cancer cells led to increases in the numbers of trypan blue-positive and active-caspase 3-positive cells, as well as suppression of tumor-sphere formation and cell migration. Furthermore, the amount of CASP3 and PARP mRNA and the level of cleaved caspase-3 protein were enhanced in PKCλ-deficient ALDH1high cells. An Apoptosis inhibitor (z-VAD-FMK) suppressed the enhancement of cell death as well as the levels of cleaved caspase-3 protein in PKCλ deficient ALDH1high cells. It also altered the asymmetric/symmetric distribution ratio of ALDH1A3 protein. In addition, PKCλ knockdown led to increases in cellular ROS levels in ALDH1high cells. These results suggest that PKCλ is essential for cancer cell survival and migration, tumorigenesis, the asymmetric distribution of ALDH1A3 protein among cancer cells, and the maintenance of low ROS levels in ALDH1-positive breast cancer stem cells. This makes it a key contributor to the poorer prognosis seen in late-stage breast cancer patients.
Subject(s)
Aldehyde Oxidoreductases/metabolism , Biomarkers, Tumor/metabolism , Breast Neoplasms/mortality , Gene Expression Regulation, Neoplastic , Isoenzymes/metabolism , Neoplastic Stem Cells/pathology , Protein Kinase C/metabolism , Adult , Aged , Aged, 80 and over , Apoptosis , Breast Neoplasms/metabolism , Breast Neoplasms/pathology , Cell Movement , Cell Proliferation , Female , Follow-Up Studies , Humans , Middle Aged , Neoplastic Stem Cells/metabolism , Prognosis , Survival Rate , Tumor Cells, CulturedABSTRACT
BACKGROUND/AIM: Co-expression of c-Met and ALDH1A3 indicates a poor prognosis in stage III-IV breast cancers and contributes to cell proliferation and tumor formation by ALDH1-positive breast CSCs. PKCλ is overexpressed and contributes to a poor prognosis in several cancers. MATERIALS AND METHODS: A breast cancer genomics data set (METABRIC, n=2509) was downloaded and analyzed, as was the effect c-Met and PKCλ inhibitors on ALDH1high cell viability and tumor-sphere formation. RESULTS: c-Met expression correlates with expression of PKCλ in breast cancer. Stage III-IV breast cancer patients with c-Methigh PKCλhigh ALDH1A3high have a poorer prognosis than patients with c-Metlow PKCλlow ALDH1A3low Foretinib and auranofin suppressed cell viability and tumor-sphere formation by ALDH1high cells. These results suggest that c-Met and PKCλ are cooperatively involved in cancer progression and contribute to poor prognoses in breast cancer. CONCLUSION: c-Met and PKCλ are potentially useful prognostic markers and therapeutic targets in late-stage breast cancer.
