A human T lymphotropic virus type I (HTLV-I) long terminal repeat-directed antisense c-myc construct with an Epstein-Barr virus replicon vector inhibits cell growth in a HTLV-I-transformed human T cell line

Loss of FBXW7-mediated degradation of BRAF elicits resistance to BET inhibitors in adult T cell leukemia cells

Background

Human T cell leukemia virus type 1 (HTLV-1)-associated adult T cell leukemia (ATL) has a very poor prognosis with a median survival of 8 months and a 4-year overall survival of 11% for acute ATL. Present treatment options are limited and there is no curative therapy for ATL. Ubiquitin ligase FBXW7 is commonly mutated or functionally inactivated in human cancers. Consistent with the notion that FBXW7 controls the degradation of many oncoproteins, loss of FBXW7 has been linked to increased drug resistance or sensitivity in cancer cells.

Method

In this study, we have characterized FBXW7 mutants previously identified in HTLV-I-infected ATL patient samples. TET-inducible ATL cells carrying wild type or mutated FBXW7 were analyzed for target degradation and for drug sensitivity.

Results

Our results demonstrate that mutations in FBXW7 can selectively disrupt ubiquitination and proteasome degradation of target proteins: c-MYC, cyclin E and MCL1. Both c-MYC and MYCN were highly expressed in uncultured ATL patient’s samples and ATL-derived cell lines; and ATL cells demonstrated sensitivity to BET inhibitors in vitro and in vivo. High-throughput reverse phase protein array revealed BRAF as a novel target of FBXW7 and further experiments showed that mutations in FBXW7 preventing degradation of BRAF provided resistance to BET inhibitors. In contrast to R465, hot spot FBXW7 mutations at R505C retained degradation of BRAF but not NOTCH1, c-MYC, cyclin E, or MCL1. Finally, a combination therapy using BET inhibitors along with a BRAF or an ERK inhibitor prevented tumor cell resistance and growth.

Conclusion

Our results suggest that FBXW7 status may play an important role in drug therapy resistance of cancer cells. Genetic characterization of FBXW7 may be one factor included in future personalized cancer treatment identification.

Tissue-selective expression of dominant-negative proteins for the regulation of vascular smooth muscle cell proliferation

The transcription factors c-myb and c-myc are essential for vascular smooth muscle cell (VSMC) replication and are rapidly induced following mitogenic stimulation of quiescent VSMCs in vitro and in vivo following balloon catheter injury. Consequently, interference with c-myb and c-myc function provides a possible avenue for the prevention of VSMC proliferation associated with intimal hyperplasia. We have carried out studies focused on the inhibition of VSMC proliferation using dominant-negative gene constructs incorporating the DNA-binding domains of the c-myb or c-myc genes fused to the repressor domain of the Drosophila engrailed gene. Transient transfection of rat, rabbit and human vascular SMCs results in a dramatic inhibition of proliferation for at least 72 h after transfection. Furthermore, this inhibition of cellular proliferation was found to be due, at least in part, to the induction of apoptosis. Coupling expression of the chimeric dominant-negative proteins to transcriptional regulatory elements of the human vascular smooth muscle alpha-actin gene allows specific targeting of vascular smooth muscle cells.

Analysis of Tax-expressing cell lines generated from HTLV-I tax-transgenic mice: correlation between c-myc overexpression and neoplastic potential

Human T-cell leukemia/lymphotropic virus type I (HTLV-I) infection causes a variety of human diseases, including adult T-cell leukemia/lymphoma. The viral transactivator Tax has been implicated as a key factor in the HTLV-I-induced transformation pathway. To investigate the components of this pathway, we derived fibroblast-like cell lines, designated T6 and T9, from tail biopsies of tax-transgenic C57BL/6 mice that do not develop tumors. Phenotypic characterization of T6 and T9 cells and T6-derived subclones revealed that they differ in their abilities to form foci in vitro and tumors in vivo. The observed differences in the levels of Tax expression did not correlate with their degree of neoplastic potential. However, a control cell line derived from a nontransgenic C57BL/6 mouse did not form foci in vitro or tumors in vivo, indicating that Tax was required for the transformation process. Results of Northern analyses showed that the T9 cells and the highly malignant derivatives of T6 cells expressed elevated levels of c-myc mRNA. These findings suggest that progression of the tax-transgenic cells toward a more malignant phenotype might involve c-myc deregulation.

Antisense inhibition of virus infections

This chapter summarizes the new approaches to identify novel antiviral drug targets and to develop novel antiviral strategies. The chapter also reviews genetic pharmacology as it relates to antiviral antisense research and drug development. Antisense oligonucleotides are selective compounds by virtue of their interaction with specific segments of RNA. For potential antivirals, identification of appropriate target RNA sequences for antisense oligonucleotides is performed at two levels: the optimal gene within the virus, and the optimal sequence within the RNA. The importance of these oligonucleotide modifications in designing effective drugs is just now being evaluated, both in animal model systems and in the clinic. The first generation of widely used antisense oligonucleotides has been the phosphorothioate (PS) compounds and a body of data on biodistribution, pharmacokinetics, and metabolism in animals and in humans is now available. Since the identification and sequencing of human immunodeficiency virus (HIV), there has been a strong interest in identifying a potent oligonucleotide inhibitor that would have the potential for development as a therapy for acquired immunodeficiency syndrome (AIDS). Numerous phosphorothioate oligonucleotides, with no apparent antisense sequence specificity, can have an anti-herpes simplex virus (HSV) effect. Oligonucleotides can be effective anti-influenza agents in cell culture assays. Hepatitis B virus (HBV) X protein that is a transactivator has been also reported to be targeted successfully by antisense oligonucleotides in vivo. Several of picornaviruses have been targets for antisense oligonucleotide inhibition, and the studies demonstrate the versatility of the antisense approach. However, the fact that oligonucleotides may contribute numerous mechanisms toward the antiviral activity, in addition to the antisense mechanism, may in some cases be an asset in the pursuit of clinically useful antiviral drugs.