KPT-330 Prevents Aortic Valve Calcification via a Novel C/EBPß Signaling Pathway.

[Figure: see text].

Tgfß1-Cthrc1 Signaling Plays an Important Role in the Short-Term Reparative Response to Heart Valve Endothelial Injury.

OBJECTIVE: Aortic valve disease is a common worldwide health burden with limited treatment options. Studies have shown that the valve endothelium is critical for structure-function relationships, and disease is associated with its dysfunction, damage, or injury. Therefore, therapeutic targets to maintain a healthy endothelium or repair damaged endothelial cells could hold promise. In this current study, we utilize a surgical mouse model of heart valve endothelial cell injury to study the short-term response at molecular and cellular levels. The goal is to determine if the native heart valve exhibits a reparative response to injury and identify the mechanisms underlying this process. Approach and Results: Mild aortic valve endothelial injury and abrogated function was evoked by inserting a guidewire down the carotid artery of young (3 months) and aging (16-18 months) wild-type mice. Short-term cellular responses were examined at 6 hours, 48 hours, and 4 weeks following injury, whereas molecular profiles were determined after 48 hours by RNA-sequencing. Within 48 hours following endothelial injury, young wild-type mice restore endothelial barrier function in association with increased cell proliferation, and upregulation of transforming growth factor beta 1 (Tgfß1) and the glycoprotein, collagen triple helix repeat containing 1 (Cthrc1). Interestingly, this beneficial response to injury was not observed in aging mice with known underlying endothelial dysfunction. CONCLUSIONS: Data from this study suggests that the healthy valve has the capacity to respond to mild endothelial injury, which in short term has beneficial effects on restoring endothelial barrier function through acute activation of the Tgfß1-Cthrc1 signaling axis and cell proliferation.

SAMHD1 suppresses innate immune responses to viral infections and inflammatory stimuli by inhibiting the NF-κB and interferon pathways.

Sterile alpha motif and HD-domain-containing protein 1 (SAMHD1) blocks replication of retroviruses and certain DNA viruses by reducing the intracellular dNTP pool. SAMHD1 has been suggested to down-regulate IFN and inflammatory responses to viral infections, although the functions and mechanisms of SAMHD1 in modulating innate immunity remain unclear. Here, we show that SAMHD1 suppresses the innate immune responses to viral infections and inflammatory stimuli by inhibiting nuclear factor-κB (NF-κB) activation and type I interferon (IFN-I) induction. Compared with control cells, infection of SAMHD1-silenced human monocytic cells or primary macrophages with Sendai virus (SeV) or HIV-1, or treatment with inflammatory stimuli, induces significantly higher levels of NF-κB activation and IFN-I induction. Exogenous SAMHD1 expression in cells or SAMHD1 reconstitution in knockout cells suppresses NF-κB activation and IFN-I induction by SeV infection or inflammatory stimuli. Mechanistically, SAMHD1 inhibits NF-κB activation by interacting with NF-κB1/2 and reducing phosphorylation of the NF-κB inhibitory protein IκBα. SAMHD1 also interacts with the inhibitor-κB kinase ε (IKKε) and IFN regulatory factor 7 (IRF7), leading to the suppression of the IFN-I induction pathway by reducing IKKε-mediated IRF7 phosphorylation. Interactions of endogenous SAMHD1 with NF-κB and IFN-I pathway proteins were validated in human monocytic cells and primary macrophages. Comparing splenocytes from SAMHD1 knockout and heterozygous mice, we further confirmed SAMHD1-mediated suppression of NF-κB activation, suggesting an evolutionarily conserved property of SAMHD1. Our findings reveal functions of SAMHD1 in down-regulating innate immune responses to viral infections and inflammatory stimuli, highlighting the importance of SAMHD1 in modulating antiviral immunity.

Regulation of deoxynucleotide metabolism in cancer: novel mechanisms and therapeutic implications.

Regulation of intracellular deoxynucleoside triphosphate (dNTP) pool is critical to genomic stability and cancer development. Imbalanced dNTP pools can lead to enhanced mutagenesis and cell proliferation resulting in cancer development. Therapeutic agents that target dNTP synthesis and metabolism are commonly used in treatment of several types of cancer. Despite several studies, the molecular mechanisms that regulate the intracellular dNTP levels and maintain their homeostasis are not completely understood. The discovery of SAMHD1 as the first mammalian dNTP triphosphohydrolase provided new insight into the mechanisms of dNTP regulation. SAMHD1 maintains the homeostatic dNTP levels that regulate DNA replication and damage repair. Recent progress indicates that gene mutations and epigenetic mechanisms lead to downregulation of SAMHD1 activity or expression in multiple cancers. Impaired SAMHD1 function can cause increased dNTP pool resulting in genomic instability and cell-cycle progression, thereby facilitating cancer cell proliferation. This review summarizes the latest advances in understanding the importance of dNTP metabolism in cancer development and the novel function of SAMHD1 in regulating this process.

Phospholipid Scramblase 1, an interferon-regulated gene located at 3q23, is regulated by SnoN/SkiL in ovarian cancer cells.

BACKGROUND: Treatment of advanced stage ovarian cancer continues to be challenging due to acquired drug resistance and lack of early stage biomarkers. Genes identified to be aberrantly expressed at the 3q26.2 locus (i.e. SnoN/SkiL) have been implicated in ovarian cancer pathophysiology. We have previously shown that SnoN expression is increased in advanced stage ovarian cancers and alters cellular response to arsenic trioxide (As2O3). FINDINGS: We now demonstrate increased DNA copy number levels (TCGA data) of phospholipid scramblase 1 (PLSCR1, located at 3q23) whose transcript expression in ovarian cell lines is highly correlated with SnoN mRNA. Interestingly, SnoN can modulate PLSCR1 mRNA levels in the absence/presence of interferon (IFN-2α). Both IFN-2α and As2O3 treatment can modulate PLSCR1 mRNA levels in ovarian carcinoma cells. However, SnoN siRNA does not lead to altered PLSCR1 protein implicating other events needed to modulate its protein levels. In addition, we report that PLSCR1 can modulate aspects of the As2O3 cellular response. CONCLUSIONS: Our findings warrant further investigation into the role of PLSCR1 in ovarian cancer development and chemoresistance.

Studies on the antimicrobial properties of N-acylated ciprofloxacins.

Fluoroquinolone antibiotics have been a mainstay in the treatment of bacterial diseases. The most notable representative, ciprofloxacin, possesses potent antimicrobial activity; however, a rise in resistance to this agent necessitates development of novel derivatives to prolong the clinical lifespan of these antibiotics. Herein we have synthesized and analyzed the antimicrobial properties of a library of N-acylated ciprofloxacin analogues. We find that these compounds are broadly effective against Gram-positive and Gram-negative bacteria, with many proving more effective than the parental drug, and several possessing MICs ≤1.0 µg/ml against methicillin-resistant Staphylococcus aureus and Bartonella species. An analysis of spontaneous mutation frequencies reveals very low potential for resistance in MRSA compared to existing fluoroquinolones. Mode of action profiling reveals that modification of the piperazinyl nitrogen by acylation does not alter the effect of these molecules towards their bacterial target. We also present evidence that these N-acylated compounds are highly effective at killing intracellular bacteria, suggesting the suitability of these antibiotics for therapeutic treatment.

Single-cell transcriptomic profiling unveils dysregulation of cardiac progenitor cells and cardiomyocytes in a mouse model of maternal hyperglycemia.

Congenital heart disease (CHD) is the most prevalent birth defect, often linked to genetic variations, environmental exposures, or combination of both. Epidemiological studies reveal that maternal pregestational diabetes is associated with ~5-fold higher risk of CHD in the offspring; however, the causal mechanisms affecting cardiac gene-regulatory-network (GRN) during early embryonic development remain poorly understood. In this study, we utilize an established murine model of pregestational diabetes to uncover the transcriptional responses in key cell-types of the developing heart exposed to maternal hyperglycemia (matHG). Here we show that matHG elicits diverse cellular responses in E9.5 and E11.5 embryonic hearts compared to non-diabetic hearts by single-cell RNA-sequencing. Through differential-gene-expression and cellular trajectory analyses, we identify perturbations in genes, predominantly affecting Isl1+ second heart field progenitors and Tnnt2+ cardiomyocytes with matHG. Using cell-fate mapping analysis in Isl1-lineage descendants, we demonstrate that matHG impairs cardiomyocyte differentiation and alters the expression of lineage-specifying cardiac genes. Finally, our work reveals matHG-mediated transcriptional changes in second heart field lineage that elevate CHD risk by perturbing Isl1-GRN during cardiomyocyte differentiation. Gene-environment interaction studies targeting the Isl1-GRN in cardiac progenitor cells will have a broader impact on understanding the mechanisms of matHG-induced risk of CHD associated with diabetic pregnancies.

miR-145 transgenic mice develop cardiopulmonary complications leading to postnatal death.

BACKGROUND: Both downregulation and elevation of microRNA miR-145 has been linked to an array of cardiopulmonary phenotypes, and a host of studies suggest that it is an important contributor in governing the differentiation of cardiac and vascular smooth muscle cell types. METHODS AND RESULTS: To better understand the role of elevated miR-145 in utero within the cardiopulmonary system, we utilized a transgene to overexpress miR-145 embryonically in mice and examined the consequences of this lineage-restricted enhanced expression. Overexpression of miR-145 has detrimental effects that manifest after birth as overexpressor mice are unable to survive beyond postnatal day 18. The miR-145 expressing mice exhibit respiratory distress and fail to thrive. Gross analysis revealed an enlarged right ventricle, and pulmonary dysplasia with vascular hypertrophy. Single cell sequencing of RNA derived from lungs of control and miR-145 transgenic mice demonstrated that miR-145 overexpression had global effects on the lung with an increase in immune cells and evidence of leukocyte extravasation associated with vascular inflammation. CONCLUSIONS: These data provide novel findings that demonstrate a pathological role for miR-145 in the cardiopulmonary system that extends beyond its normal function in governing smooth muscle differentiation.

Biology and Biomechanics of the Heart Valve Extracellular Matrix.

Heart valves are dynamic structures that, in the average human, open and close over 100,000 times per day, and 3 × 109 times per lifetime to maintain unidirectional blood flow. Efficient, coordinated movement of the valve structures during the cardiac cycle is mediated by the intricate and sophisticated network of extracellular matrix (ECM) components that provide the necessary biomechanical properties to meet these mechanical demands. Organized in layers that accommodate passive functional movements of the valve leaflets, heart valve ECM is synthesized during embryonic development, and remodeled and maintained by resident cells throughout life. The failure of ECM organization compromises biomechanical function, and may lead to obstruction or leaking, which if left untreated can lead to heart failure. At present, effective treatment for heart valve dysfunction is limited and frequently ends with surgical repair or replacement, which comes with insuperable complications for many high-risk patients including aged and pediatric populations. Therefore, there is a critical need to fully appreciate the pathobiology of biomechanical valve failure in order to develop better, alternative therapies. To date, the majority of studies have focused on delineating valve disease mechanisms at the cellular level, namely the interstitial and endothelial lineages. However, less focus has been on the ECM, shown previously in other systems, to be a promising mechanism-inspired therapeutic target. Here, we highlight and review the biology and biomechanical contributions of key components of the heart valve ECM. Furthermore, we discuss how human diseases, including connective tissue disorders lead to aberrations in the abundance, organization and quality of these matrix proteins, resulting in instability of the valve infrastructure and gross functional impairment.

SAMHD1 modulates in vitro proliferation of acute myeloid leukemia-derived THP-1 cells through the PI3K-Akt-p27 axis.

Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) is a mammalian dNTP hydrolase that acts as a negative regulator in the efficacy of cytarabine treatment against acute myeloid leukemia (AML). However, the role of SAMHD1 in AML development and progression remains unknown. We have reported that SAMHD1 knockout (KO) in the AML-derived THP-1 cells results in enhanced proliferation and reduced apoptosis, but the underlying mechanisms are unclear. Here we show that SAMHD1 KO in THP-1 cells increased PI3K activity and reduced expression of the tumor suppressor PTEN. Pharmacological inhibition of PI3K activity reduced cell proliferation specifically in SAMHD1 KO cells, suggesting that SAMHD1 KO-induced cell proliferation is mediated via enhanced PI3K signaling. However, PI3K inhibition did not significantly affect SAMHD1 KO-reduced apoptosis, implicating the involvement of additional mechanisms. SAMHD1 KO also led to enhanced phosphorylation of p27 at residue T157 and its mis-localization to the cytoplasm. Inhibition of PI3K activity reversed these effects, indicating that SAMHD1 KO-induced changes in p27 phosphorylation and localization is mediated via PI3K-Akt signaling. While SAMHD1 KO significantly enhanced THP-1 cell migration in vitro, SAMHD1 KO attenuated the ability of THP-1 cells to form subcutaneous tumors in xenografted immunodeficient mice. This effect correlated with significantly increased expression of tumor necrosis factor α (TNF-α) in tumors, which may suggest that TNF-α-mediated inflammation could account for the decreased tumorigenicity in vivo. Our findings implicate that SAMHD1 can regulate AML cell proliferation via modulation of the PI3K-Akt-p27 signaling axis, and that SAMHD1 may affect tumorigenicity by downregulating inflammation.

SAMHD1 inhibits epithelial cell transformation in vitro and affects leukemia development in xenograft mice.

Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) is a mammalian dNTP hydrolase (dNTPase) and functions as a negative regulator in the efficacy of cytarabine treatment of acute myeloid leukemia (AML). We have reported that SAMHD1 knockout (KO) increased the activity of phosphoinositide 3-kinase (PI3K) in AML-derived THP-1 cells and attenuated their ability to form subcutaneous tumors in xenografted immunodeficient mice. However, the functional significance of SAMHD1 in controlling AML leukemogenesis remains unclear. Previous studies show that in vitro transformation of Madin-Darby canine kidney (MDCK) epithelial cells by the Jaagsiekte sheep retrovirus (JSRV) envelope protein requires activation of the PI3K/Akt oncogenic signaling pathway. Using this cell transformation model, we demonstrated that ectopic expression of wild-type human SAMHD1 or a dNTPase-defective SAMHD1 mutant (HD/AA) significantly inhibited MDCK cell transformation, but did not affect cell proliferation. To visualize and quantify THP-1 cell growth and metastasis in xenografted immunodeficient mice, we generated luciferase-expressing stable SAMHD1 KO THP-1 cells and control THP-1 cells, which were injected intravenously into immunodeficient mice. Bioluminescence imaging and quantification analysis of xenografted mice revealed that SAMHD1 KO cell-derived tumors had similar growth and metastatic potential compared with control cells at 35 days post-injection. However, mice xenografted with SAMHD1 KO cells showed greater survival compared with mice injected with control cells. Our data suggest that exogenous SAMHD1 expression suppresses in vitro cell transformation independently of its dNTPase activity, and that endogenous SAMHD1 affects AML tumorigenicity and disease progression in vivo.

MicroRNA-181 contributes to downregulation of SAMHD1 expression in CD4+ T-cells derived from Sèzary syndrome patients.

Sézary syndrome (SS) is a rare subtype of cutaneous T-cell lymphoma (CTCL) that is characterized by aggressive spread of neoplastic CD4+ T-cells from the skin into the bloodstream with metastasis to visceral organs. The deoxynucleoside triphosphohydrolase SAMHD1 is highly expressed in normal CD4+ T-cells, while its expression is down-regulated in CD4+ T-cells from SS patients. MicroRNA (miR) dysregulation is an important epigenetic mechanism in the pathogenesis and progression of SS. MiR-181 has been shown to inhibit SAMHD1 expression in cell lines and was identified as an important prognostic biomarker in CTCL. However, whether SAMHD1 is down-regulated by miR-181 in primary CD4+ T-cells of SS patients is unknown. Compared to normal CD4+ T-cells, SAMHD1 protein expression is significantly reduced in transformed CD4+ T-cell lines and CD4+ T-cells from SS patients, which inversely correlates with increased miR-181 levels in these cells. Over-expression of miR-181b in primary CD4+ T-cells from healthy donors significantly decreased SAMHD1 protein level, but not mRNA level. In contrast, inhibition of miR-181 in a CD4+ T-cell line significantly increased the level of SAMHD1 protein expression. Our results demonstrate that miR-181 is an important regulator of SAMHD1 protein expression in neoplastic CD4+ T-cells, likely through a mechanism of translational inhibition.

Exogenous expression of SAMHD1 inhibits proliferation and induces apoptosis in cutaneous T-cell lymphoma-derived HuT78 cells.

Sterile α motif and HD domain-containing protein 1 (SAMHD1) is a mammalian dNTP hydrolase (dNTPase) that regulates intracellular dNTP balance. We have previously reported that SAMHD1 mRNA and protein levels are significantly downregulated in CD4+ T-cells of patients with cutaneous T-cell lymphoma (CTCL), a disease characterized by infiltration of neoplastic CD4+ T-lymphocytes into the skin. However, functional significance of SAMHD1 in CTCL development and progression remains unknown. Here we investigate the mechanism by which SAMHD1 induces apoptosis in CTCL-derived CD4+ T-cells. We stably expressed exogenous SAMHD1 in the CTCL-derived HuT78 T-cell line containing a very low level of endogenous SAMHD1 protein. We found that low-level exogenous expression of SAMHD1 led to a significant reduction in HuT78 cell growth, proliferation, and colony formation. Exogenous SAMHD1 expression in HuT78 cells also resulted in increased spontaneous and Fas ligand (Fas-L)-induced apoptosis levels via activation of the extrinsic pathway, including caspase-8, -3 and -7. Additionally, increased SAMHD1 significantly reduced the protein and mRNA expression of the short isoform of cFLIP (cFLIPS), an important negative regulator of Fas-L-mediated apoptotic signaling. Our results indicate that exogenous SAMHD1 expression inhibits HuT78 cell growth and proliferation in part by increasing apoptosis. These findings implicate that SAMHD1 acts as an inhibitor in CTCL cell growth, suggesting that downregulation of SAMHD1 expression in neoplastic T-cells can facilitate uncontrolled cell proliferation.

Induction of PLSCR1 in a STING/IRF3-dependent manner upon vector transfection in ovarian epithelial cells.

Toll-like receptors (TLRs) are the primary sensors of the innate immune system that recognize pathogenic nucleic acids including double-stranded plasmid DNA (dsDNA). TLR signaling activates multiple pathways including IRF3 which is involved in transcriptional induction of inflammatory cytokines (i.e. interferons (IFNs)). Phospholipid scramblase 1, PLSCR1, is a highly inducible IFN-regulated gene mediating anti-viral properties of IFNs. Herein, we report a novel finding that dsDNA transfection in T80 immortalized normal ovarian surface epithelial cell line leads to a marked increase in PLSCR1 mRNA and protein. We also noted a comparable response in primary mammary epithelial cells (HMECs). Similar to IFN-2α treated cells, de novo synthesized PLSCR1 was localized predominantly to the plasma membrane. dsDNA transfection, in T80 and HMEC cells, led to activation of MAPK and IRF3. Although inhibition of MAPK (using U0126) did not modulate PLSCR1 mRNA and protein, IRF3 knockdown (using siRNA) significantly ablated the PLSCR1 induction. In prior studies, the activation of IRF3 was shown to be mediated by cGAS-STING pathway. To investigate the contribution of STING to PLSCR1 induction, we utilized siRNA to reduce STING expression and observed that PLSCR1 protein was markedly reduced. In contrast to normal T80/HMECs, the phosphorylation of IRF3 as well as induction of STING and PLSCR1 were absent in ovarian cancer cells (serous, clear cell, and endometrioid) suggesting that the STING/IRF3 pathway may be dysregulated in these cancer cells. However, we also noted induction of different TLR and IFN mRNAs between the T80 and HEY (serous epithelial ovarian carcinoma) cell lines upon dsDNA transfection. Collectively, these results indicate that the STING/IRF3 pathway, activated following dsDNA transfection, contributes to upregulation of PLSCR1 in ovarian epithelial cells.

Roles and regulation of phospholipid scramblases.

Phospholipid scramblase activity is involved in the collapse of phospholipid (PL) asymmetry at the plasma membrane leading to externalization of phosphatidylserine. This activity is crucial for initiation of the blood coagulation cascade and for recognition/elimination of apoptotic cells by macrophages. Efforts to identify gene products associated with this activity led to the characterization of PL scramblase (PLSCR) and XKR family members which contribute to phosphatidylserine exposure in response to apoptotic stimuli. Meanwhile, TMEM16 family members were identified to externalize phosphatidylserine in response to elevated calcium in Scott syndrome platelets, which is critical for activation of the coagulation cascade. Herein, we report their mechanisms of gene regulation, molecular functions independent of their scrambling activity, and their potential roles in pathogenic conditions.

SnoN/SkiL expression is modulated via arsenic trioxide-induced activation of the PI3K/AKT pathway in ovarian cancer cells.

SnoN/SkiL (TGFß regulator) is dysregulated in ovarian cancer, a disease associated with acquired drug-resistance. Arsenic trioxide (As2O3, used in treating APL) induces SnoN to oppose the apoptotic response in ovarian cancer cells. We now report that As2O3 increases phosphorylation of EGFR/p66ShcA and EGFR degradation. As2O3 activates Src(Y416) whose activity (inhibited by PP2) modulates EGFR activation, its interaction with Shc/Grb2, and p-AKT. Inhibition of PI3K reduces SnoN and cell survival. Although EGFR or MAPK1 siRNA did not alter SnoN expression, As2O3-induced cleaved PARP was reduced together with increased XIAP. Collectively, As2O3 mediates an initial rise in pY-Src(416) to regulate the PI3K/AKT pathway which increases SnoN and cell survival; these early events may counter the cell death response associated with increased pY-EGFR/MAPK activation.