PARP-1 regulates DNA repair factor availability.

PARP-1 holds major functions on chromatin, DNA damage repair and transcriptional regulation, both of which are relevant in the context of cancer. Here, unbiased transcriptional profiling revealed the downstream transcriptional profile of PARP-1 enzymatic activity. Further investigation of the PARP-1-regulated transcriptome and secondary strategies for assessing PARP-1 activity in patient tissues revealed that PARP-1 activity was unexpectedly enriched as a function of disease progression and was associated with poor outcome independent of DNA double-strand breaks, suggesting that enhanced PARP-1 activity may promote aggressive phenotypes. Mechanistic investigation revealed that active PARP-1 served to enhance E2F1 transcription factor activity, and specifically promoted E2F1-mediated induction of DNA repair factors involved in homologous recombination (HR). Conversely, PARP-1 inhibition reduced HR factor availability and thus acted to induce or enhance BRCA-ness . These observations bring new understanding of PARP-1 function in cancer and have significant ramifications on predicting PARP-1 inhibitor function in the clinical setting

Identification of NF-kB-like Transcription Factor In Arabidopsis Thaliana

NF-kB is a transcription factor that plays an important role in innate and adaptive immune responses. Dysregulation of this factor leads to many anti-apoptotic as well as pro-inflammatory disorders. Although NF-kB is present in animal cells, it has not been positively identified in plant cells. Circumstantial evidence, however, leads us to speculate on the presence of a NF-kB-like transcription factor in plants. It has been shown that the NIM1 protein from the plant Arabidopsis thaliana shares significant identity with IkB, an inhibitor of the NF-kB protein. Similarly, the presence of putative kB DNA sequences upstream of some genes in the Arabidopsis genome also indicates the possible presence of an NF-kB like factor in plants. This study was conducted to identify an NF-kB-like transcription factor in plants. We used consensus animal NF-kB sequences and five different Arabidopsis putative kB-like sequences and used a bioinformatic approach to examine their presence and location around Arabidopsis genes, upstream of their transcription start sites. We also determined if plant proteins interact with these sequences in order to identify plant protein(s) that bind to any of these sequences using electrophoretic mobility shift assays. We found that protein(s) in the extract from Arabidopsis showed binding interaction with putative kB-like sequences in vitro, indicating the possible presence of NF-kB like-proteins in plants. Given the known importance of NFkB pathway in animal cells, identification of NFkB-like proteins in plant cells will deepen our insights into mechanistic basis of immune regulation in plants. Findings of this study will help to further dissect the defense mechanism in plants, including A. thaliana

MAPK Reliance via Acquired CDK4/6 Inhibitor Resistance in Cancer.

Purpose: Loss of cell-cycle control is a hallmark of cancer, which can be targeted with agents, including cyclin-dependent kinase-4/6 (CDK4/6) kinase inhibitors that impinge upon the G1-S cell-cycle checkpoint via maintaining activity of the retinoblastoma tumor suppressor (RB). This class of drugs is under clinical investigation for various solid tumor types and has recently been FDA-approved for treatment of breast cancer. However, development of therapeutic resistance is not uncommon. Experimental Design: In this study, palbociclib (a CDK4/6 inhibitor) resistance was established in models of early stage, RB-positive cancer. Results: This study demonstrates that acquired palbociclib resistance renders cancer cells broadly resistant to CDK4/6 inhibitors. Acquired resistance was associated with aggressive in vitro and in vivo phenotypes, including proliferation, migration, and invasion. Integration of RNA sequencing analysis and phosphoproteomics profiling revealed rewiring of the kinome, with a strong enrichment for enhanced MAPK signaling across all resistance models, which resulted in aggressive in vitro and in vivo phenotypes and prometastatic signaling. However, CDK4/6 inhibitor-resistant models were sensitized to MEK inhibitors, revealing reliance on active MAPK signaling to promote tumor cell growth and invasion. Conclusions: In sum, these studies identify MAPK reliance in acquired CDK4/6 inhibitor resistance that promotes aggressive disease, while nominating MEK inhibition as putative novel therapeutic strategy to treat or prevent CDK4/6 inhibitor resistance in cancer

Suppression of Adaptive Responses to Targeted Cancer Therapy by Transcriptional Repression

Acquired drug resistance is a major factor limiting the effectiveness of targeted cancer therapies. Targeting tumors with kinase inhibitors induces complex adap- tive programs that promote the persistence of a fraction of the original cell population, facilitating the eventual outgrowth of inhibitor-resistant tumor clones. We show that the addition of a newly identified CDK7/12 inhibitor, THZ1, to targeted therapy enhances cell killing and impedes the emergence of drug-resistant cell populations in diverse cellular and in vivo cancer models. We propose that targeted therapy induces a state of transcriptional dependency in a subpopulation of cells poised to become drug tolerant, which THZ1 can exploit by blocking dynamic transcriptional responses, promoting remodeling of enhancers and key signaling outputs required for tumor cell survival in the setting of targeted therapy. These findings suggest that the addition of THZ1 to targeted therapies is a promising broad-based strategy to hinder the emergence of drug-resistant cancer cell populations. SIGNIFICANCE: CDK7/12 inhibition prevents active enhancer formation at genes, promoting resistance emergence in response to targeted therapy, and impedes the engagement of transcriptional programs required for tumor cell survival. CDK7/12 inhibition in combination with targeted cancer therapies may serve as a therapeutic paradigm for enhancing the effectiveness of targeted therapies