Abid R. Mattoo

The Participation of myeloid cell leukemia‐1 (MCL‐1), an antiapoptotic protein, in DNA repair and homologous recombination (HR) is not well understood. This study tests whether MCL‐1 interacts with Males absent On First (MOF) to regulate H4K16 acetylation that promotes HR repair in response to replication stress induced by Hydroxyurea (HU) treatment. Co‐immunoprecipitation of FLAG‐MCL‐1 from cancer cells treated with HU pulls down a complex of MCL‐1, MOF and BH3‐interacting domain death agonist (BID). The same complex is pulled down in cells treated with HU that express FLAG‐MOF. MCL‐1 regulates H4K16 acetylation during HU‐induced replication stress since knockdown of MCL‐1 decreases H4K16 acetylation while re‐expression of MCL‐1 restores H4K16 acetylation. Furthermore, knockdown of BID rescues the clonogenic survival in MCL‐1 depleted cells in response to replication stress which is associated with decreased Caspase 3/7 activity compared to MCL‐1 depleted cells. Cells depleted in both MCL‐1 and BID display increased HR repair efficiency by direct repeats‐green fluorescent protein assay and in response to HU exhibit increased ATR, Chk1, and RPA phosphorylation relative to MCL‐1 depleted cells. This study uncovers that MCL‐1 cooperates with MOF and regulates HR repair through H4K16 acetylation. Further, this study determines that MCL‐1 and BID cooperate to regulate the crosstalk between HR repair and apoptosis.

Mycobacterium tuberculosis is a human pathogen that can thrive inside the host immune cells for several years and cause tuberculosis. This is due to the propensity of M. tuberculosis to synthesize a sturdy cell wall, shift metabolism and growth, secrete virulence factors to manipulate host immunity, and exhibit stringent response. These attributes help M. tuberculosis to manage the host response, and successfully establish and maintain an infection even under nutrient-deprived stress conditions for years. In this review, we will discuss the importance of mycobacterial stringent response under different stress conditions. The stringent response is mediated through small signaling molecules called alarmones “(pp)pGpp”. The synthesis and degradation of these alarmones in mycobacteria are mediated by Rel protein, which is both (p)ppGpp synthetase and hydrolase. Rel is important for all central dogma processes—DNA replication, transcription, and translation—in addition to regulating virulence, drug resistance, and biofilm formation. Rel also plays an important role in the latent infection of M. tuberculosis. Here, we have discussed the literature on alarmones and Rel proteins in mycobacteria and highlight that (p)ppGpp-analogs and Rel inhibitors could be designed and used as antimycobacterial compounds against M. tuberculosis and non-tuberculous mycobacterial infections.

NANOG is an embryonic transcription factor, which gets reexpressed in cancer stem or tumor initiating cells. NANOGP8, a retrogene belonging to the NANOG family, is predominantly expressed in cancer cells and shows very high similarity with NANOG both at the nucleotide and at the protein level. The high similarity makes it extremely challenging to distinguish between these two transcription factors. Here we describe a highly efficient restriction endonuclease-based assay, which is performed on cDNA and allows to distinguish NANOGP8 from NANOG. This assay is critical to understand the specific role of NANOGP8 in cancer stemness, which in turn helps to unravel the therapeutic potential of targeting this undruggable transcription factor through gene therapy, for treatment of various cancers.

MCL-1, a member of the antiapoptotic BCL-2 family, is a prosurvival protein with an essential DNA repair function. This study aims to test whether inhibition of protein synthesis by mTOR complex (mTORC) inhibitors depletes MCL-1, suppresses homologous recombination (HR) repair, and sensitizes cancer cells to PARP inhibitors. Treatment with everolimus decreases MCL-1 in colorectal carcinomas and small cell lung cancer (SCLC) cells but not glioblastoma multiforme (GBM) cells with a PTEN mutational background. However, AZD2014, a dual mTORC inhibitor, depletes MCL-1 in GBMs. Further, we show that everolimus decreases 4EBP1 phosphorylation only in colorectal carcinoma, whereas AZD2014 decreases 4EBP1 phosphorylation in both colorectal carcinoma and GBM cells. Combination therapy using everolimus or AZD2014 with olaparib inhibits the growth of clone A and U87-MG xenografts in in vivo and decreases clonogenic survival in in vitro compared with monotherapy. Reintroduction of MCL-1 rescues the survival of cancer cells in response to combination of everolimus or AZD2014 with olaparib. Treatment of cells with mTORC inhibitors and olaparib increases γ-H2AX and 53BP1 foci, decreases BRCA1, RPA, and Rad51 foci, impairs phosphorylation of ATR/Chk1 kinases, and induces necroptosis. In summary, mTORC inhibitors deplete MCL-1 to suppress HR repair and increase sensitivity to olaparib both in in vitro and in xenografts.Implications: Targeting the DNA repair activity of MCL-1 in in vivo for cancer therapy has not been tested. This study demonstrates that depleting MCL-1 sensitizes cancer cells to PARP inhibitors besides eliciting necroptosis, which could stimulate antitumor immunity to improve the therapeutic intervention of cancers.

Myeloid cell leukemia-1 (MCL-1) is a pro-survival BCL-2 protein family member highly expressed in hematopoietic stem cells (HSCs) and regulated by growth factor signals that manifest anti-apoptotic activity. Here we report that depletion of MCL-1, but not its isoform MCL1S, increases genomic instability and cell sensitivity to ionizing radiation (IR) induced death. MCL-1 association with genomic DNA increased post-irradiation and it co-localized with 53BP1 in foci. Post-irradiation, MCL-1 depleted cells exhibited decreased γ-H2AX foci, decreased phosphorylation of ATR and higher levels of residual 53BP1 and RIF1 foci, suggesting DNA DSB repair by homologous recombination (HR) was compromised. Consistent with this model, MCL-1 depleted cells have a reduced frequency of IR-induced BRCA1, RPA and Rad51 foci formation, decreased DNA end resection and decreased HR repair in the DR-GFP DSB repair model. Similarly, after HU induction of stalled replication forks in MCL-1 depleted cells there was a decreased ability to subsequently restart DNA synthesis, which is normally dependent upon HR mediated resolution of collapsed forks. Therefore, the present data support a model whereby MCL-1 depletion increases 53BP1 and RIF1 co-localization at DSBs, which inhibits BRCA1 recruitment, and sensitizes cells to DSBs from IR or stalled replication forks that require HR for repair.

β2-spectrin depletion impairs DNA damage repair

Purpose: High levels of BCL-2 family members in colorectal carcinoma cause resistance to treatment. Inhibition of NANOG or its paralog NANOGP8 reduces the proliferation, stemness, and tumorigenicity of colorectal carcinoma cells. Our hypothesis was that inhibition of NANOG/NANOGP8 enhances the cytotoxic effect of BH3 mimetics targeting BCL-2 family members in colorectal carcinoma cells through reducing expression of MCL-1, a prosurvival BCL-2 protein. Experimental Design: Lentiviral vector (LV) shRNA to NANOG (shNG-1) or NANOGP8 (shNp8-1) transduced colorectal carcinoma cells that were also exposed to the BH3 mimetics ABT-737 or ABT-199 in vivo in colorectal carcinoma xenografts and in vitro where proliferation, protein and gene expression, and apoptosis were measured. Results: Clone A and CX-1 were sensitive to ABT-737 and ABT-199 at IC_50s of 2 to 9 μmol/L but LS174T was resistant with IC_50s of 18 to 30 μmol/L. Resistance was associated with high MCL-1 expression in LS174T. LVshNG-1 or LVshNp8-1 decreased MCL-1 expression, increased apoptosis, and decreased replating efficiency in colorectal carcinoma cells treated with either ABT-737 or ABT-199 compared with the effects of either BH3 mimetic alone. Inhibition or overexpression of MCL-1 alone replicated the effects of LVshNG-1 or LVshNp8-1 in increasing or decreasing the apoptosis caused with the BH3 mimetic. The combination therapy inhibited the growth of LS174T xenografts in vivo compared with untreated controls or treatment with only LV shRNA or ABT-737. Conclusions: Inhibition of NANOGP8 or NANOG enhances the cytotoxicity of BH3 mimetics that target BCL-2 family members. Gene therapy targeting the NANOGs may increase the efficacy of BH3 mimetics in colorectal carcinoma. Clin Cancer Res; 20(21); 5446–55. ©2014 AACR.