ABSTRACT
The female hormone progesterone (P4) promotes the expansion of stem-like cancer cells in estrogen receptor (ER)- and progesterone receptor (PR)-positive breast tumors. The expanded tumor cells lose expression of ER and PR, express the tumor-initiating marker CD44, the progenitor marker cytokeratin 5 (CK5) and are more resistant to standard endocrine and chemotherapies. The mechanisms underlying this hormone-stimulated reprogramming have remained largely unknown. In the present study, we investigated the role of microRNAs in progestin-mediated expansion of this dedifferentiated tumor cell population. We demonstrate that P4 rapidly downregulates miR-29 family members, particularly in the CD44(+) cell population. Downregulation of miR-29 members potentiates the expansion of CK5(+) and CD44(+) cells in response to progestins, and results in increased stem-like properties in vitro and in vivo. We demonstrate that miR-29 directly targets Krüppel-like factor 4 (KLF4), a transcription factor required for the reprogramming of differentiated cells to pluripotent stem cells, and for the maintenance of breast cancer stem cells. These results reveal a novel mechanism, whereby progestins increase the stem cell-like population in hormone-responsive breast cancers, by decreasing miR-29 to augment PR-mediated upregulation of KLF4. Elucidating the mechanisms whereby hormones mediate the expansion of stem-like cells furthers our understanding of the progression of hormone-responsive breast cancers.
Subject(s)
Breast Neoplasms/genetics , Cell Differentiation/genetics , Kruppel-Like Transcription Factors/genetics , MicroRNAs/genetics , Progestins/pharmacology , 3' Untranslated Regions , Animals , Breast Neoplasms/drug therapy , Breast Neoplasms/pathology , Cell Differentiation/drug effects , Cell Line, Tumor , Female , Gene Expression Regulation, Neoplastic/drug effects , Humans , Hyaluronan Receptors/metabolism , Kruppel-Like Factor 4 , Kruppel-Like Transcription Factors/metabolism , Mice , Mice, SCID , MicroRNAs/metabolism , Progesterone/pharmacology , Up-Regulation , Xenograft Model Antitumor AssaysABSTRACT
A novel extreme alkaliphile was isolated from a mine water containment dam at 3.2 km below land surface in an ultra-deep gold mine near Carletonville, South Africa. The cells of this bacterium were straight to slightly curved rods, motile by flagella and formed endospores. Growth was observed over the temperature range 20-50 degrees C (optimum 40 degrees C; 45 min doubling time) and pH range 8.5-12.5 (optimum pH 10.0). The novel isolate, one of the most alkaliphilic micro-organisms yet described, was a strictly anaerobic chemo-organotroph capable of utilizing proteinaceous substrates such as yeast extract, peptone, tryptone and casein. Elemental sulfur, thiosulfate or fumarate, when included as accessory electron acceptors, improved growth. The G+C content of genomic DNA was 36.4 mol %. Phylogenetic analysis based on the 16S rDNA sequence indicated that the isolate is a member of cluster XI within the low G+C gram-positive bacteria, but only distantly related to previously described members. On the basis of physiological and molecular properties, the isolate represents a novel species, for which the name Alkaliphilus transvaalensis gen. nov., sp. nov. is proposed (type strain SAGM1T = JCM 10712T = ATCC 700919T). The mechanism of generation of the highly alkaline microbial habitat and the possible source of the alkaliphile are discussed.