A novel isoform of the B cell tyrosine kinase BTK protects breast cancer cells from apoptosis.

Tyrosine kinases orchestrate key cellular signaling pathways and their dysregulation is often associated with cellular transformation. Several recent cases in which inhibitors of tyrosine kinases have been successfully used as anticancer agents have underscored the importance of this class of proteins in the development of targeted cancer therapies. We have carried out a large-scale loss-of-function analysis of the human tyrosine kinases using RNA interference to identify novel survival factors for breast cancer cells. In addition to kinases with known roles in breast and other cancers, we identified several kinases that were previously unknown to be required for breast cancer cell survival. The most surprising of these was the cytosolic, nonreceptor tyrosine kinase, Bruton's tyrosine kinase (BTK), which has been extensively studied in B cell development. Down regulation of this protein with RNAi or inhibition with pharmacological inhibitors causes apoptosis; overexpression inhibits apoptosis induced by Doxorubicin in breast cancer cells. Our results surprisingly show that BTK is expressed in several breast cancer cell lines and tumors. The predominant form of BTK found in tumor cells is transcribed from an alternative promoter and results in a protein with an amino-terminal extension. This alternate form of BTK is expressed at significantly higher levels in tumorigenic breast cells than in normal breast cells. Since this protein is a survival factor for these cells, it represents both a potential marker and novel therapeutic target for breast cancer.

Sensitivity to splicing modulation of BCL2 family genes defines cancer therapeutic strategies for splicing modulators.

Dysregulation of RNA splicing by spliceosome mutations or in cancer genes is increasingly recognized as a hallmark of cancer. Small molecule splicing modulators have been introduced into clinical trials to treat solid tumors or leukemia bearing recurrent spliceosome mutations. Nevertheless, further investigation of the molecular mechanisms that may enlighten therapeutic strategies for splicing modulators is highly desired. Here, using unbiased functional approaches, we report that the sensitivity to splicing modulation of the anti-apoptotic BCL2 family genes is a key mechanism underlying preferential cytotoxicity induced by the SF3b-targeting splicing modulator E7107. While BCL2A1, BCL2L2 and MCL1 are prone to splicing perturbation, BCL2L1 exhibits resistance to E7107-induced splicing modulation. Consequently, E7107 selectively induces apoptosis in BCL2A1-dependent melanoma cells and MCL1-dependent NSCLC cells. Furthermore, combination of BCLxL (BCL2L1-encoded) inhibitors and E7107 remarkably enhances cytotoxicity in cancer cells. These findings inform mechanism-based approaches to the future clinical development of splicing modulators in cancer treatment.

Clinical application of a cancer genomic profiling assay to guide precision medicine decisions.

AIM: Develop and apply a comprehensive and accurate next-generation sequencing based assay to help clinicians to match oncology patients to therapies. MATERIALS & METHODS: The performance of the CANCERPLEX® assay was assessed using DNA from well-characterized routine clinical formalin-fixed paraffin-embedded (FFPE) specimens and cell lines. RESULTS: The maximum sensitivity of the assay is 99.5% and its accuracy is virtually 100% for detecting somatic alterations with an allele fraction of as low as 10%. Clinically actionable variants were identified in 93% of patients (930 of 1000) who underwent testing. CONCLUSION: The test's capacity to determine all of the critical genetic changes, tumor mutation burden, microsatellite instability status and viral associations has important ramifications on clinical decision support strategies, including identification of patients who are likely to benefit from immune checkpoint blockage therapies.

N-terminal control of small heat shock protein oligomerization: changes in aggregate size and chaperone-like function.

The small heat shock protein superfamily is composed of proteins from throughout the phylogenetic spectrum that are induced upon environmental stress. Their structural stability under stress derives in large part from the central region of the proteins, which forms two beta sheets held together by hydrophobic interactions and appears to be present in all superfamily members. The length, sequence, and amino acid composition of the N- and C-terminals, in contrast, are quite variable. The role of the N-terminal has been hypothesized to control species-specific assembly of subunits into higher level structures. To test this, a set of constructs was designed and expressed: the N-terminal sequences preceding the start of the core regions of alphaA-crystallin and HSP 16.5 from Methanococcus jannaschii were swapped; the N-terminal of each protein was removed, and replaced with a brief N-terminal extension sequence; and two nonsense N-terminal sequences of approximately the same length and hydropathicity as the original replaced the alphaA-crystallin N-terminal. All constructs, plus the original recombinant sequences, could be overexpressed except for the 16.5 N-terminal extension, and all showed chaperone-like activity except for the hybrid with the 16.5 C-terminal. Size and properties of the replacement N-terminal place limits on aggregate size. Additional restrictions are imposed by the structure of the dimer.

From cancer genomes to oncogenic drivers, tumour dependencies and therapeutic targets.

The analysis of human cancer by genome sequencing and various types of arrays has proved that many tumours harbour hundreds of genes that are mutated or substantially altered by copy number changes. But how many of these changes are meaningful? And how can we exploit these massive data sets to yield new targets for cancer treatment? In this Opinion article, we describe emerging approaches that aim to determine which altered genes are actually contributing to cancer, as well as their potential as therapeutic targets.

An RNA interference screen identifies metabolic regulators NR1D1 and PBP as novel survival factors for breast cancer cells with the ERBB2 signature.

Overexpression of the adverse prognostic marker ERBB2 occurs in 30% of breast cancers; however, therapies targeting this gene have not proved to be as effective as was initially hoped. Transcriptional profiling meta-analyses have shown that there are approximately 150 genes co-overexpressed with ERBB2, suggesting that these genes may represent alternative factors influencing ERBB2-positive tumors. Here we describe an RNA interference-based analysis of these genes that identifies transcriptional regulators of fat synthesis and storage as being critical for the survival of these cells. These transcription factors, nuclear receptor subfamily 1, group D, member 1 (NR1D1) and peroxisome proliferator activated receptor gamma binding protein (PBP), both reside on ERBB2-containing 17q12-21 amplicons and are part of the ERBB2 expression signature. We show that NR1D1 and PBP act through a common pathway in upregulating several genes in the de novo fatty acid synthesis network, which is highly active in ERBB2-positive breast cancer cells. Malate dehydrogenase 1 and malic enzyme 1, enzymes that link glycolysis and fatty acid synthesis, are also regulated by NR1D1. The resulting high-level fat production from increased expression of these genes likely contributes to an abnormal cellular energy metabolism based on aerobic glycolysis. Together, these results show that the cells of this aggressive form of breast cancer are genetically preprogrammed to depend on NR1D1 and PBP for the energy production necessary for survival.

Global gene expression profiles associated with retinoic acid-induced differentiation of embryonal carcinoma cells.

We have evaluated the effects of retinoic acid (RA) treatment of F9 embryonal carcinoma (EC) cells, which induces differentiation into primitive endoderm, on gene expression patterns. F9 cells were exposed to RA in culture, and global expression patterns were examined with cDNA-based microarrays at early (8 hr) and later times (24 hr) after exposure. Of the 1,176 known transcripts examined, we identified 57 genes (4.8%) that were responsive to RA at 8 and/or 24 hr: 35 were induced, 20 were repressed, and 2 were differentially regulated at these time points. To determine if our results were dependent on the array technology employed, we also evaluated the response to RA at 24 hr with oligonucleotide-based arrays. With these more dense arrays (12,488 genes), we identified an additional 353 RA-regulated genes (2.8%): 173 were upregulated and 180 were downregulated. Thus, a total of 410 genes regulated by RA were identified with roughly equivalent numbers induced or repressed. Although the expression of many genes found on both array platforms was consistent, the results for some genes were disparate. Quantitative PCR studies on a subset of these genes supported the results obtained with the cDNA arrays. Our results confirmed the regulation of several known RA-responsive genes and we also identified a number of genes not previously known to be RA-responsive. Those novel genes that were induced presumably contribute to the cellular processes required for a shift from proliferation to differentiation, whereas those new genes that were downregulated may possibly contribute to the maintenance of cell proliferation.

Structural diversity in the small heat shock protein superfamily: control of aggregation by the N-terminal region.

The small heat shock protein superfamily, extending over all kingdoms, is characterized by a common core domain with variable N- and C-terminal extensions. The relatively hydrophobic N-terminus plays a critical role in promoting and controlling high-order aggregation, accounting for the high degree of structural variability within the superfamily. The effects of N-terminal volume on aggregation were studied using chimeric and truncated proteins. Proteins lacking the N-terminal region did not aggregate above the tetramers, whereas larger N-termini resulted in large aggregates, consistent with the N-termini packing inside the aggregates. Variation in an extended internal loop differentiates typical prokaryotic and plant superfamily members from their animal counterparts; this implies different geometry in the dimeric building block of high-order aggregates.