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Background/aim: Sirtuins (SIRTs) play crucial roles in various signaling pathways that modulate differentiation and proliferation. We sought to elucidate the role of SIRTs in differentiation and proliferation of human neuroblastoma (NB)., Materials and Methods: NB cells were treated with nicotinamide (NAM), a non-specific SIRT inhibitor, SIRT-targeted short hairpin RNAs, and retinoic acid to assess cell growth and differentiation., Results: SIRTs are involved in proliferation and differentiation using NAM in BE(2)-C cells. Specifically, SIRT6 knockdown in BE(2)-C cells reduced cell proliferation, induced neurite extension, corresponding with induction of p21 CIP1 expression and G 1 cell-cycle arrest. These effects were rescued by forced re-overexpression of SIRT6. SIRT6 expression was reduced in differentiated human NB sections, and RA-induced differentiation in BE(2)-C cells., Conclusion: SIRTs have important oncogenic properties in NB beyond its established functions in aging and genome stability. SIRT6 may represent a novel target for developing future therapeutics for the treatment of aggressive NBs., (Copyright© 2018, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Pyruvate dehydrogenase E1α (PDHA1) is the first component enzyme of the pyruvate dehydrogenase (PDH) complex that transforms pyruvate, via pyruvate decarboxylation, into acetyl-CoA that is subsequently used by both the citric acid cycle and oxidative phosphorylation to generate ATP. As such, PDH links glycolysis and oxidative phosphorylation in normal as well as cancer cells. Herein we report that SIRT3 interacts with PDHA1 and directs its enzymatic activity via changes in protein acetylation. SIRT3 deacetylates PDHA1 lysine 321 (K321), and a PDHA1 mutant mimicking a deacetylated lysine (PDHA1(K321R)) increases PDH activity, compared to the K321 acetylation mimic (PDHA1(K321Q)) or wild-type PDHA1. Finally, PDHA1(K321Q) exhibited a more transformed in vitro cellular phenotype compared to PDHA1(K321R). These results suggest that the acetylation of PDHA1 provides another layer of enzymatic regulation, in addition to phosphorylation, involving a reversible acetyllysine, suggesting that the acetylome, as well as the kinome, links glycolysis to respiration., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Purpose: To identify genes whose depletion is detrimental to Pim1-overexpressing prostate cancer cells and to validate this finding in vitro and in vivo., Experimental Design: RNAi screening was used to identify genes whose depletion is detrimental to Pim1-overexpressing cells. Our finding was validated using shRNA or PLK1-specific inhibitor BI 2536. Xenograft studies were performed using both PLK1-knockdown cells and BI 2536 to investigate the effects of PLK1 inhibition on tumorigenesis in Pim1-overexpressing cells. Finally, PLK1 and PIM1 expression patterns in human prostate tumors were examined by immunohistochemistry using tissue microarrays., Results: We identified the mitotic regulator polo-like kinase (PLK1) as a gene whose depletion is particularly detrimental to the viability of Pim1-overexpressing prostate cancer. Inhibition of PLK1 by shRNA or BI 2536 in Pim1-overexpressing prostate cancer xenograft models resulted in a dramatic inhibition of tumor progression. Notably, Pim1-overexpressing cells were more prone to mitotic arrest followed by apoptosis due to PLK1 inhibition than control cells. Furthermore, inhibition of PLK1 led to the reduction of MYC protein levels both in vitro and in vivo. Our data also suggest that PIM1 and PLK1 physically interact and PIM1 might phosphorylate PLK1. Finally, PLK1 and PIM1 are frequently co-expressed in human prostate tumors, and co-expression of PLK1 and PIM1 was significantly correlated to higher Gleason grades., Conclusions: Our findings demonstrate that PIM1-overexpressing cancer cells are particularly sensitive to PLK1 inhibition, suggesting that PIM1 might be used as a marker for identifying patients who will benefit from PLK1 inhibitor treatment., (©2014 American Association for Cancer Research.)

The infiltration of monocytes into the CNS represents one of the early steps to inflammatory events in AIDS-related encephalitis and dementia. Increased activity of selected matrix metalloproteinases (MMPs) such as MMP-9 impairs the integrity of blood-brain barrier leading to enhanced monocyte infiltration into the CNS. In this study, we examined the effect of HIV-1 Tat on the expression of MMP-9 in CRT-MG human astroglioma cells. Treatment of CRT-MG cells with HIV-1 Tat protein significantly increased protein levels of MMP-9, as measured by Western blot analysis, zymography and an ELISA. Treatment of CRT-MG cells with HIV-1 Tat protein markedly increased mRNA levels of MMP-9, as analyzed by RT-PCR. Pretreatment of CRT-MG cells with NF-kappaB inhibitors led to decrease in Tat-induced protein and mRNA expression of MMP-9. Pretreatment of CRT-MG cells with MAPK inhibitors suppressed Tat-induced MMP-9 expression. Furthermore, HIV-1 Tat-induced expression of MMP-9 was significantly inhibited by neutralization of TNF-alpha, but not IL-1beta and IL-6. Taken together, our results indicate that HIV-1 Tat can up-regulate expression of MMP-9 via MAPK-NF-kappaB-dependent mechanisms as well as Tat-induced TNF-alpha production in astrocytes.

One of characteristic features of AIDS-related encephalitis and dementia is the infiltration of monocytes into the CNS. HIV-1 Tat was demonstrated to facilitate monocyte entry into the CNS. In this study, we examined the effect of HIV-1 Tat on the expression of adhesion molecules, generation of reactive oxygen species (ROS) and NF-kappaB activation in CRT-MG human astroglioma cells. Treatment of CRT-MG cells with HIV-1 Tat protein significantly increased protein and mRNA levels of ICAM-1 and VCAM-1, as measured by Western blot analysis and RT-PCR, indicating that Tat increases these protein levels at an mRNA level. In addition, Tat induced the activation of NF-kappaB in astrocytes. Treatment of CRT-MG with NF-kappaB inhibitors led to decrease in Tat-induced protein and mRNA expression of ICAM-1 and VCAM-1. Furthermore, HIV-1 Tat protein increased ROS generation. Inhibition of Tat-induced ROS generation by N-acetyl cysteine, vitamin C and diphenyl iodonium suppressed Tat-induced NF-kappaB activation, ICAM-1 and VCAM-1 expression, and monocyte adhesion in CRT-MG. These data indicate that HIV-1 Tat can modulate monocyte adhesiveness by increasing expression of adhesion molecules such as ICAM-1 and VCAM-1 via ROS- and NF-kappaB-dependent mechanisms in astrocytes.

The infiltration of both monocyte and activated T cells in the skin is one of critical steps in the development of UVB-induced inflammation. Upregulation of adhesion molecules such as intercellular adhesion molecule 1 (ICAM-1) on the surface of keratinocytes plays an important role in this process. In this study, we examined the molecular mechanism responsible for UVB-induced expression of ICAM-1 and subsequent monocyte adhesion by keratinocyte. We observed that (1) UVB induced protein and mRNA expression of ICAM-1 in a dose- and time-dependent manner in human keratinocyte cell HaCaT; (2) UVB induced the translocation of NF-kappaB and inhibition of NF-kappaB by NF-kappaB inhibitors suppressed UVB-induced mRNA and protein expression of ICAM-1; (3) UVB increased the intracellular level of reactive oxygen species (ROS) by HaCaT cells; (4) UVB-induced increase of intracellular ROS level was suppressed by pretreatment with diphenyl iodonium (DPI) and N-acetyl cysteine (NAC); and (5) inhibition of UVB-induced ROS production by DPI or NAC suppressed UVB-mediated translocation of NF-kappaB, expression of ICAM-1 and subsequent monocyte adhesion in HaCaT cells. These results suggest that UVB-induced ROS is involved in the translocation of NF-kappaB which is responsible for expression of ICAM-1 and subsequent increased monocyte adhesion in human keratinocyte.