Down-regulation Of C-myc Gene Research Articles

The anticancer effects of pharmacological inhibition of autophagy in acute erythroid leukemia cells.

Although recent studies have reported different aspects of autophagy, from pro-survival to pro-death roles of this process in malignant cells, the underlying mechanisms by which autophagy inhibitors contribute toward the induction of programmed cell death in cancerous cells are still unclear. In the present study, we have attempted to explore some of the molecular features of pharmacological inhibition of autophagy in TF-1 cells (an acute erythroid leukemia model). Our findings indicated that ara-C induces autophagy (with alteration of LC3B, p62, and Beclin-1) in the cells; however, targeting autophagy by 3-methyladenine and chloroquine significantly increased caspase-dependent apoptosis and the sub-G1 compartment in ara-C-treated cells. Moreover, cell cycle analysis showed that 3-MA, as an early-stage autophagy inhibitor, could elevate the cell population in the G0/G1 cell cycle phase, which was associated with upregulation of p21 and p27 expressions. Interestingly, autophagy inhibition was also accompanied by downregulation of c-Myc gene and protein expression levels and upregulated levels of Bax and Bak gene expressions. In addition, following inhibition of autophagy, the levels of tumor-suppressive miRNA (i.e. miR-204) increased, whereas the values of oncogenic miRNAs (including miR-21, miR-221, miR-30a, and miR-17) decreased. Overall, our experiments indicate that autophagy inhibitors (especially chloroquine) seem to be promising agents for combination therapy in acute erythroid leukemia.

Potential tumor suppressive function of miR-196b in B-cell lineage acute lymphoblastic leukemia

Keeping in view the fact that genes coding microRNAs (miRNAs) have been found to be localized in chromosomal regions susceptible to genetic translocations, this study was addressed to identify and characterize the miRNAs that are present near/within the regions involved in genetic translocations characteristic of B-cell acute lymphoblastic leukemia (B-cell ALL). Out of six such identified miRNAs miR-196b was not only found to be significantly down-regulated in both EB-3 cell line as well as B-cell ALL patients as compared to that found in the corresponding controls, but also had the inherent capacity to down-regulate the highly expressed c-myc gene, a consequence of genetic translocation characteristic of EB-3 cells at both transcriptional and translational level. This phenomenon was in conformity with the observed reciprocal relationship between the expressed genes coding for miR-196b and c-myc in B-cells derived from ALL patients as well as c-myc gene was found to be a putative target of miR-196b as predicted by bioinformatic algorithms. Also down-regulation of c-myc gene was accompanied by decreased expressions of c-myc effector genes coding for hTERT, Bcl-2, and AATF. Based upon these results, we propose for the first time that miR-196b has the inherent capacity to down-regulate the overamplified c-myc gene recognized as a common pathognomonic feature leading to cancer in general and B-cell ALL in particular. Hence miR-196b can be assigned with the tumor suppressor function and can be of therapeutic importance in paving the way toward the treatment of B-cell ALL.

Functional characterization of AATF transcriptome in human leukemic cells

The study, addressed to explore the transcriptional expression and regulation of Apoptosis-antagonizing transcription factor (AATF) gene within various types of human leukemic cell lines, revealed that AATF gene was overexpressed ubiquitously in all the leukemic cell lines studied and this upregulation was accompanied by c-myc gene overamplification in these cells. Downregulation of AATF gene transcription within leukemic cells not only resulted in the downregulation of c-myc gene and vice-versa but also contributed to apoptosis leading to cell death. Further, the link between AATF expression and leukemic cellular apoptosis involved PI3K/Akt pathway. Based on these results we propose that AATF gene may be of crucial importance in maintaining the leukemic state of a cell compartment through its ability to initiate cell proliferation coupled with repression of cellular apoptosis.

Apoptosis and Mitotic Arrest Are Two Independent Effects of the Protein Phosphatases Inhibitor Okadaic Acid in K562 Leukemia Cells

Treatment of human myeloid leukemia K562 cells with the serine/threonine protein phosphatases inhibitor okadaic acid induced mitotic arrest followed by apoptosis in a synchronized manner. The effect was observed at drug concentrations that inhibited the protein phosphatase type 2A but not type 1. We investigated whether apoptosis was a consequence of the preceding mitosis arrest or was induced independently by okadaic acid. We found that (1) apoptosis, but not mitotic arrest, was inhibited in cells with constitutive expression of Bcl-2; (2) pretreatment of cells with the DNA synthesis inhibitor hydroxyurea blocked the mitotic arrest but not the apoptosis mediated by okadaic acid; (3) down-regulation of c-myc gene was associated with apoptosis, but not with mitotic arrest; and (4) inhibition of protein synthesis abrogated mitotic arrest, but not apoptosis. The results suggest that inhibition of protein phosphatase 2A by okadaic acid provokes mitotic arrest and apoptosis of leukemia cells by independent mechanisms.

Transforming Growth Factor-β1 Induces Apoptosis through Down-Regulation of c-mycGene and Overexpression of p27Kip1Protein in Cervical Carcinoma

Transforming growth factor-β1 (TGF-β1) is known to be a potent growth inhibitor for many cell types, including most epithelial cells. In skin keratinocytes, TGF-β1 has been shown to inhibit growth and to rapidly reduce c-mycexpression. However, the molecular mechanism of TGF-β1 action on cell growth of cervical carcinoma has not yet been elucidated. We thus assessed the effect of TGF-β1 on the growth of cervical carcinoma cell lines. Two cervical squamous carcinoma cell lines, CUMC-3 and CUMC-6, were incubated with varying concentrations of TGF-β1, and growth inhibition was evaluated with tetrazolium-based colorimetric assay. After culture in TGF-β1 for 24 h, inhibition of growth was detected in a dose-dependent manner at concentrations of 0.1–10 ng/ml in both cell lines. This effect of TGF-β1 on cultured carcinoma cells was associated with apoptotic process including oligonucleosomal ladder DNA and apoptotic body formations. Northern blot analysis revealed c-mycmRNA expression was suppressed by 10 ng/ml of TGF-β1 following 3 h of treatment in both cell lines. Western blot analysis showed that the level of p27Kip1protein was increased after TGF-β1 treatment in both cell lines. These results suggest that the mechanisms by which TGF-β1 inhibits the growth of cervical carcinoma are complex and may include effects on down-regulation of c-mycgene, and overexpression of p27Kip1protein.