lls compared to their ALDH2 counterparts. KLF4 belongs to zinc finger family of transcription factors, which has been reported to be critical for the maintenance of breast cancer stem cells and their aggressive behavior such as migration and invasion ad resistance to cisplatin . However, other stem cell mediators like BMI1, c-myc, Oct3/4 and S100A1 did not show any noticeable changes in their expression compared with ALDH2 phenotypes . ALDH1A1 isotype PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19672638 Celgosivir promotes ovarian cancer stem-like cells’ properties Consistent with the CSC literature, our data revealed elevated expression of ALDH1A1 isozyme in the platinum resistant A2780/CP70 cells. To further evaluate the role of ALDH1A1 in maintenance of cancer stem-like cells properties of platinum resistant ovarian cancer cells, we have downregulated ALDH1A1 specific isozyme using shRNAs. Contrary to its high expression, downregulation of ALDH1A1 has not shown any considerable differences in invasive properties of these cells. However, ALDH1A1 knockdown affected their ALDH1A1 Maintains Stem-Like Properties by Altered DNA Repair Networks ability to form colonies in soft agar, demonstrating a 2.5-fold decrease in the colonies . Similarly, downregulation of ALDH1A1 alone significantly sensitized inherently PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19673983 platinum resistant A2780/CP70 cells to carboplatin. Considering IC50 doses required for these cells, about 50% reduction in carboplatin dose is evident for ALDH1A1 knockdown cells . Together, these data suggests that ALDH1A1 status is one of the critical factors in maintaining stemlike cell properties and platinum resistance in ovarian 
cancer. ALDH1A1 controls cell cycle checkpoints by regulation of KLF4 and p21 proteins Increased expression of KLF4 in ALDH+ cells led us to evaluate any functional relationship between ALDH1A1 and KLF4. Although ALDH1A1 knockdown did not affect the level of KLF4 mRNA, a significant decrease in KLF4 protein levels was evidenced in these cells. Considering that the functional status of the cell cycle regulator p21 is intimately related to KLF4’s function, the mRNA and protein levels of p21 were also assessed. As expected, both ALDH1A1 transcript and ALDH1A1 Maintains Stem-Like Properties by Altered DNA Repair Networks protein levels of p21 were dramatically decreased in ALDH1A1 deficient A2780/CP70 cells. Since ALDH1A1 status influenced expression of cell cycle checkpoint proteins p21/ CDK4, we further analyzed the cell cycle profiles of these cells. The flow cytometric data clearly indicate decreased G1 cell population and a compensatory increase in accumulation of cells in S and G2 phases. Due to the fact that cells in active replication are more vulnerable to genotoxic stress compared to their non-dividing or other restive phases, the re-sensitization of ALDH1A1 deficient cells may be in part attributable to the changes in cell cycle distribution. Furthermore, we have also confirmed that KLF4 status affects p21 expression levels in A2780/CP70 cells. However, evaluation of ALDH activity and ALDH1A1 expression in cells did not exhibit any noticeable changes, suggesting KLF4 likely serves downstream to ALDH1A1. To further evaluate the genes responsible for chemoresistance and cell cycle regulation based on the status of ALDH1A1, we have used RT2 Profiler PCR Array for the human Cancer Drug Resistance & Cell Cycle. The comparative expression profiles of genes in ALDH1A1 knockdown vs. control cells revealed a significant decrease in expression of the cell cycle regula
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