Suppression of OCT-1 in Metastatic Breast Cancer Cells Reduces Tumor Metastatic Potential, Hypoxia Resistance, and Drug Resistance.

OCT-1/POU2F1 is a ubiquitously expressed transcription factor. Its expression starts at the earliest stage of embryonic development. OCT-1 controls genes involved in the regulation of differentiation, proliferation, cell metabolism, and aging. High levels of OCT-1 transcription factor in tumor cells correlate with tumor malignancy and resistance to antitumor therapy. Here, we report that suppression of OCT-1 in breast cancer cells reduces their metastatic potential and drug resistance. OCT-1 knockdown in the MDA-MB231 breast cancer cells leads to a fivefold decrease (p < 0.01) in cell migration rates in the Boyden chamber. A decrease in the transcription levels of human invasion signature (HIS) genes (ARHGDIB, CAPZA2, PHACTR2, CDC42, XRCC5, and CAV1) has been also demonstrated by real-time PCR, with high expression of these genes being a hallmark of actively metastasizing breast cancer cells. Transcriptional activity of ATF6 response elements is significantly reduced in the cell lines with decreased OCT-1 expression, which results in lower levels of adaptive EPR stress response. OCT-1 knockdown more than two times increases the MDA-MB231 cell death rate in hypoxia and significantly increases the doxorubicin or docetaxel-treated MDA-MB231 cell death rate. Our findings indicate that OCT-1 may be an important therapeutic target and its selective inhibition may have significant therapeutic effects and may improve prognosis in breast cancer patients.

Triple-negative and triple-positive breast cancer cells reciprocally control their growth and migration via the S100A4 pathway.

The study's aim was to investigate the S100A4-mediated mechanisms of the regulation of tumor cell proliferation and migration in the human triple-positive breast carcinoma cell line MCF-7 (TPBC) and triple-negative breast carcinoma cell line MDA-MB-231 (TNBC). The proliferative activity of TNBC more than doubled during the incubation in the conditioned medium of TPBC. Extracellular S100A4 dose-dependently decreased the proliferative response of TPBC. TPBC negatively impacted the growth of TNBCs during their co-culturing. TPBC significantly decreased the migration activity of the TNBC cells while the S100A4 intracellular level in the TNBC was also decreasing. The decrease in the S100A4 intracellular level occurred due to the protein's monomeric form while the contribution of the dimeric form into the overall S100A4 concentration in TNBC cells increased 1.5-2-fold. The S100A4 pathway in the intercellular communication between TNBC and TPBCs also included the dexamethasone-sensitive mechanisms of S100A4 intra- and extracellular pools regulation.

Primate-specific stress-induced transcription factor POU2F1Z protects human neuronal cells from stress.

The emergence of new primate-specific genes is an essential factor in human and primate brain development and functioning. POU2F1/Oct-1 is a transcription regulator in higher eukaryotes which is involved in the regulation of development, differentiation, stress response, and other processes. We have demonstrated that the Tigger2 transposon insertion into the POU2F1 gene which occurred in the primate lineage led to the formation of an additional exon (designated the Z-exon). Z-exon-containing primate-specific Oct-1Z transcript includes a short upstream ORF (uORF) located at its 5'-end and the main ORF encoding the Oct-1Z protein isoform (Pou2F1 isoform 3, P14859-3), which differs from other Oct-1 isoforms by its N-terminal peptide. The Oct-1Z-encoding transcript is expressed mainly in human brain cortex. Under normal conditions, the translation of the ORF coding for the Oct-1Z isoform is repressed by uORF. Under various stress conditions, uORF enables a strong increase in the translation of the Oct-1Z-encoding ORF. Increased Oct-1Z expression levels in differentiating human neuroblasts activate genes controlling stress response, neural cell differentiation, brain formation, and organogenesis. We have shown that the Oct-1Z isoform of the POU2F1/Oct-1 transcription factor is an example of a primate-specific genomic element contributing to brain development and cellular stress defense.

The regulatory interplay between Oct-1 isoforms contributes to hematopoiesis and the isoforms imbalance correlates with a malignant transformation of B cells.

Oct-1(POU2F1) is a DNA-binding transcription regulator and its level being highly increased in many human cancers. Oct-1 is present in the human cells as a family of functionally different isoforms which are transcribed from alternative promoters. Here, we have demonstrated that expression patterns of Oct-1 isoforms change during differentiation of hematopoetic progenitor cells (CD34+) (HPCs) to the B (CD19+) and T (CD3+) cells. While Oct-1L is expressed at a high level in the CD34+ HPCs, its expression level drops dramatically during the T-cell differentiation, although remains nearly the same in B-cells. We have described the novel human Oct-1R isoform which is conserved in mammals and is B cell-specific. Oct-1R was found in B cells, but not in HPCs. Oct-1R is transcribed from the same promoter as Oct-1L, another lymphocyte-specific isoform. Overexpression of Oct-1R and Oct-1L in the Namalwa cells leads to the repression of many genes involved in B-lymphocyte differentiation and signal transduction. Thus these isoforms may regulate the particular stages of development of normal B cells and maintain their proper differentiation status. However the extremely high level of Oct-1L isoform observed in the B-lymphoblast tumor cell lines indicated that the excess of Oct-L seem likely to considerably decrease the differentiation ability of these cells. Oct-1 may serve as a therapeutic target for many tumors, but it should be noted that in a tumor the content of a certain isoform Oct-1, rather than the total Oct-1 protein, can be increased.

Oct-1 modifies S100A4 exchange between intra- and extracellular compartments in Namalwa cells and increases their sensitivity to glucocorticoids.

S100A4, a small intra- and extracellular Ca(2+)-binding protein, is involved in tumor progression and metastasis with S100A4 level shown to be correlated with tumor cells metastatic potential. Simultaneously, Octamer transcription factor 1 (Oct-1) regulates a wide range of genes and participates in tumor cell progression with high Oct-1 level associated with a poor prognosis for different tumors. In this study, following the establishment of Oct-1 binding site, we used Burkit lymphoma B cells (Namalwa cells) which express different isoforms of Oct-1 (Oct-1A, Oct-1L and Oct-1X) to investigate the role of Oct-1 in S100A4 expression and sustaining intra- and extra-cellular S100A4 levels. As antitumor agents, we used dexamethasone which effect is mediated by the activation of intracellular glucocorticoid receptors and camptothecin which molecular target is nuclear DNA topoisomerase I (TOP1). We established that, firstly, the most significant increase in S100A4 gene expression has been demonstrated in the cells transfected with Oct-1A. Secondly, we have established that high level of Oct-1 and decreased intracellular S100A4 level decline the survival of Namalwa cells under dexamethasone treatment. Thirdly, we have shown that the tumor cells transformation by different Oct-1 isoforms retained those cells' sensitivity to the antitumor effect of combined dexamethasone and camptothecin. In contrast, in the non-transformed Namalwa cells, dexamethasone decreased the camptothecin effect on the cells survivorship, thus, emphasizing Oct-1 role in the regulation of cell response to different antitumor agents. The results identify a necessity to consider Oct-1 level for combined chemotherapeutic drug treatment.