Chemically Induced Degradation of the Oncogenic Transcription Factor BCL6.

The transcription factor BCL6 is a known driver of oncogenesis in lymphoid malignancies, including diffuse large B cell lymphoma (DLBCL). Disruption of its interaction with transcriptional repressors interferes with the oncogenic effects of BCL6. We used a structure-based drug design to develop highly potent compounds that block this interaction. A subset of these inhibitors also causes rapid ubiquitylation and degradation of BCL6 in cells. These compounds display significantly stronger induction of expression of BCL6-repressed genes and anti-proliferative effects than compounds that merely inhibit co-repressor interactions. This work establishes the BTB domain as a highly druggable structure, paving the way for the use of other members of this protein family as drug targets. The magnitude of effects elicited by this class of BCL6-degrading compounds exceeds that of our equipotent non-degrading inhibitors, suggesting opportunities for the development of BCL6-based lymphoma therapeutics.

Ultraviolet-A and -B differentially modify the tyrosine-kinase profile of human keratinocytes and induce the expression of Arg+.

To investigate the expression profile of protein tyrosine kinases (PTKs) in normal human epidermal keratinocytes (NHEK) in response to UVA and UVB we employed a reversed transcriptase polymerase chain reaction (PCR) approach using degenerate primers derived from the conserved catalytic domain of PTKs. Quantitative real-time PCR with specific primers was used to confirm the influence of UV on the expression of the identified PTKs. Arg (Abelson-related gene, Abl2) was the PTK with the highest prevalence (30% of all PTKs) and UVA led to a further induction of Arg expression reaching nine-fold mRNA baseline expression at 17 h after irradiation. UVB was followed by an initial downregulation and a subsequent increase in Arg mRNA reaching five-fold baseline levels after 24 h. We conclude that UVA and UVB differentially modify the expression of PTKs in NHEK, and that Arg appears to have a major role in the response of keratinocytes to UV. These results provide a basis for further studies of PTK in UV-induced signaling that regulates protective responses, cell growth and carcinogenesis in the skin.

Impact of constitutive IGF1/IGF2 stimulation on the transcriptional program of human breast cancer cells.

Insulin-like growth factor (IGF) signaling is a key regulator of breast development and breast cancer. We have analyzed the expression of the IGF signaling cascade in 17 human breast cancer and 4 mammary epithelial cell lines. Five cell lines expressed high levels of IGF1 receptor, insulin (INS)/IGF receptor substrate 1, IGF-binding proteins 2 and 4, as well as the estrogen receptor (ESR), indicating a co-activation of IGF and ESR signaling. Next, we stably overexpressed IGF1 and IGF2 in MCF7 breast cancer cells, which did not affect their epithelial characteristics and the expression and localization of the epithelial marker genes E-cadherin and beta-catenin. Conversely, IGF1 and IGF2 overexpression potently increased cellular proliferation rates and the efficiency of tumor formation in mouse xenograft experiments, whereas the resistance to chemotherapeutic drugs such as taxol was unaltered. Expression profiling of overexpressing cells with whole-genome oligonucleotide microarrays revealed that 21 genes were upregulated >2-fold by both IGF1 and IGF2, 9 by IGF1, and 9 by IGF2. Half of the genes found to be upregulated are involved in transport and biosynthesis of amino acids, including several amino acid transport proteins, argininosuccinate and asparagine synthetases, and methionyl-tRNA synthetase. Upregulation of these genes constitutes a novel mechanism apparently contributing to the stimulatory effects of IGF signaling on the global protein synthesis rate. We conclude that the induction of cell proliferation and tumor formation by long-term IGF stimulation may primarily be due to anabolic effects, in particular increased amino acid production and uptake.