Chromatin nucleoprotein complexes containing tightly bound c-abl, p53 and bcl-2 gene sequences: correlation with progression of chronic myelogenous leukemia

Effects of a Particular Heptapeptide on the IFN-α-Sensitive CML Cells

Using the phage display biopanning technique, we have previously identified a heptapeptide KLWVIPQ which specifically binds to the surface of the IFN-α-sensitive but not the IFN-α-resistant CML cells. The effects of this heptapeptide on the IFN-α-sensitive CML cells were investigated in the present study. IFN-α-sensitive KT-1/A3 and IFN-α-resistant KT-1/A3R CML cells were transfected by pEGFP-KLWVIPQ expression vector and/or induced by IFN-α. WST-1 cell proliferation assay, flow cytometry, and western blotting were performed to determine the effects of this heptapeptide and/or IFN-α on CML cells. The viability of the KT-1/A3 cells was inhibited and apoptosis was induced by either expression of the heptapeptide KLWVIPQ or IFN-α treatment with concurrent upregulation of P53 and downregulation of P210^bcr/abl. However, these effects were not observed in the IFN-α-resistant KT-1/A3R cells. These results suggest that the heptapeptide KLWVIPQ shares a similar mechanism with IFN-α in the regulation of CML cell growth and apoptosis, implying that the heptapeptide KLWVIPQ could be a novel target to go further into mechanisms of IFN-α sensitivity and/or resistance in CML.

Intracellular protein trafficking kinetics in chronic myeloid leukemia stem cells using a microfluidic platform

The oncogenic fusion protein BCR-ABL is produced by chronic myeloid leukemia (CML) cells and functions as an abnormal, constitutively active tyrosine kinase that interferes with normal migratory and apoptotic behaviour of cells. Small molecule tyrosine kinase inhibitors (TKIs), such as dasatinib, eliminate CML progenitor cells, but fail to target the stem cell fraction resulting in persistent disease. In order to achieve a cure for CML in the majority of patients, we need an improved understanding of intracellular signalling dynamics, including the shuttling of BCR-ABL between cytosolic and nuclear compartments. In the past, the instability of BCR-ABL in assays using conventional immunohistochemical techniques has made this difficult and has not allowed for reliable analysis at the single cell level. Here we show how the utilization of rapid on-chip cell fixation within a microfluidic platform provides a means to immunofluorescently analyze the spatiotemporal localization of both BCR-ABL and c-ABL, as well as the linked apoptosis mediator, BCL-XL, in arrays of single CD34+ CML stem/progenitor cells, without cell loss. We demonstrate this proceeds up to 4 times faster than benchtop methods. Our results indicate that whilst both BCR-ABL and c-ABL shuttle from the cytoplasm to the nucleus following dasatinib treatment, the temporal dynamics are not synchronized. The microfluidic platform has the potential to provide insights into the intracellular signalling events in single cells. The ability to examine signalling events and assess BCR-ABL expression/activity in isolated cells in "real-time" may help elucidate the characteristics of rare CML stem cell events, which lead to the resistance of CML stem cells to TKIs.

Inhibition of Bcl-2 expression by a novel tumor-specific RNA interference system increases chemosensitivity to 5-fluorouracil in Hela cells

AIM

RNA interference (RNAi) has been proposed as a potential treatment for cancer, but the lack of cellular targets limits its use in cancer gene therapy. No current technology has achieved direct tumor-specific gene silencing using RNAi. In the present study we attempt to develop a tumor-specific RNAi system using the human telomerase reverse transcriptase (hTERT) promoter; furthermore, we analyzed its inhibitive effect on Bcl-2 expression.

METHODS

The vectors containing a small hairpin RNA (shRNA) to target exogenous reporters [firefly luciferase and enhanced green fluorescent protein (EGFP)] and endogenous gene (Bcl-2) were constructed. Luciferase expression was determined by dual luciferase assay. Reverse transcription-polymerase chain reaction (RT-PCR), fluorescence microscopy and fluorescence-activated cell sorting (FACS) were used to measure EGFP expression. Inhibition of Bcl-2 was evaluated by RT-PCR and Western blotting. Cell proliferation and viability were measured by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. FACS was used to analyze the cell cycle distribution profile.

RESULTS

We showed that with the hTERT promoter directly driving shRNA transcription, expression of the exogenous reporters (LUC and EGFP) in tumor cells, but not normal cells, was specifically inhibited in vitro. The hTERT promoter-driven shRNA also depressed the expression of Bcl-2. Inhibition of Bcl-2 did not affect cell proliferation, but increased the chemosensitivity of HeLa cells to 5-fluorouracil.

CONCLUSION

The present study describes an efficient RNAi system for gene silencing that is specific to tumor cells using the hTERT promoter. Suppression of Bcl-2 by using this system sensitized HeLa cells to 5-fluorouracil. This system may be useful for RNAi therapy.

Nucleoprotein gene tracking: localization of specific HIV-1 genes to subchromatin nucleoprotein complexes containing endonuclease activity in HIV-1-infected human cells

We developed a technique with which to isolate specific subchromatin deoxyribonucleoprotein/ribonucleoprotein precursor complexes containing discrete genes from intact mammalian nuclei by direct restriction enzyme treatment with MspI. These nucleoprotein complexes can be further fractionated and purified by two-dimensional isoelectric focusing/sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After electroelution and removal of detergent, virtually thousands of nucleoprotein complexes can be examined for the presence of tightly bound genes and enzymatic activities. Nucleoprotein gene tracking procedures were applied to study the acidic nucleoprotein complexes from steady-state human H9 cells uninfected or infected with human immunodeficiency virus type 1 (HIV-1) virus. The purified nucleoprotein complexes were screened for the presence of loosely and tightly associated HIV-1 gene sequences (pol, env, tat, and rev) using a DNA hybridization protocol. In HIV-1-infected cells, four specific nucleoprotein complexes out of several hundred were found to contain tightly bound HIV-1 pol gene sequences after purification. By contrast, the other HIV-1 gene sequences (env, tat, and rev) were not tightly bound to any of the nucleoprotein complexes in HIV-infected cells. The observations suggest that certain HIV-1 genes associate with specific chromatin nucleoprotein complexes, regardless of their pattern of DNA integration into the human genome. At least two of the HIV-1 pol-containing nucleoprotein complexes of apparent M(r) approximately 94,000, pI approximately 6.5, and M(r) approximately 47,000, pI approximately 5.1 contain DNA endonuclease activity. This was confirmed in the present study, using linearized pUC19 plasmid substrate. The technique can be used to study a variety of problems concerning the association of specific genes and enzymes with specific nucleoprotein complexes J. Cell. Biochem. Suppls. 32/33:158-165, 1999.