Francisella tularensis is a highly virulent facultative intracellular bacterium and is considered a potential biological warfare agent. Inhalation tularemia can lead to the development of bronchopneumonia, which is frequently fatal without medical intervention. Treatment strategies that directly target the respiratory mucosa may extend the efficacy of therapy, particularly for the medical management of acute aerosol exposure. To this end, we describe an intranasal (i.n.) strategy for the treatment of pulmonary Francisella infection in mice that uses a combinatorial approach with the conventional antibiotic gentamicin and interleukin 12 (IL-12). The i.n. administration of IL-12 alone promoted bacterial clearance and extended the time to death but did not prevent mortality against lethal pulmonary challenge with Francisella tularensis subsp. novicida. However, i.n. treatment with gentamicin and IL-12 therapeutically at 8 and 24 h after challenge markedly enhanced the rate of survival (70 to 100%) against pulmonary infection compared to the rates of survival for animals treated with antibiotic alone (17%) or IL-12 alone (0%). A delay in combinatorial therapy over a span of 4 days progressively decreased the efficacy of this treatment regimen. This combinatorial treatment was shown to be highly dependent upon the induction of endogenous gamma interferon and may also involve the activation of natural killer cells. Together, these findings suggest that IL-12 may be a potent adjunct for chemotherapy to enhance drug effectiveness against pulmonary Francisella infection.

During DNA polymerase switching, the Xenopus laevis Cip/Kip-type cyclin-dependent kinase inhibitor Xic1 associates with trimeric proliferating cell nuclear antigen (PCNA) and is recruited to chromatin, where it is ubiquitinated and degraded. In this study, we show that the predominant E3 for Xic1 in the egg is the Cul4-DDB1-XCdt2 (Xenopus Cdt2) (CRL4 Cdt2 ) ubiquitin ligase. The addition of full-length XCdt2 to the Xenopus extract promotes Xic1 turnover, while the N-terminal domain of XCdt2 (residues 1 to 400) cannot promote Xic1 turnover, despite its ability to bind both Xic1 and DDB1. Further analysis demonstrated that XCdt2 binds directly to PCNA through its C-terminal domain (residues 401 to 710), indicating that this interaction is important for promoting Xic1 turnover. We also identify the cis-acting sequences required for Xic1 binding to Cdt2. Xic1 binds to Cdt2 through two domains (residues 161 to 170 and 179 to 190) directly flanking the Xic1 PCNA binding domain (PIP box) but does not require PIP box sequences (residues 171 to 178). Similarly, human p21 binds to human Cdt2 through residues 156 to 161, adjacent to the p21 PIP box. In addition, we identify five lysine residues (K180, K182, K183, K188, and K193) immediately downstream of the Xic1 PIP box and within the second Cdt2 binding domain as critical sites for Xic1 ubiquitination. Our studies suggest a model in which both the CRL4 Cdt2 E3-and PIP box-containing substrates, like Xic1, are recruited to chromatin through independent direct associations with PCNA.The eukaryotic cell cycle is positively regulated by cyclindependent kinases (CDKs) and negatively regulated by CDK inhibitors (CKIs) (22,25,27,28). A complete knockout of all CDK inhibitor function, although as yet not attained in mammalian cells, has been accomplished in Saccharomyces cerevisiae and is shown to result in genomic instability due to premature entry into S phase (19). Conversely, the overexpression of cyclin E in mammalian cells has also been observed to induce chromosome instability (31). These studies suggest that CDK inhibitor function can play a critical role in maintaining genomic stability through the proper regulation of DNA replication initiation. Mammalian Cip/Kip-type CDK inhibitors p27 and p21 are stoichiometric inhibitors of CDK2-cyclins that regulate the entry into S phase and are targeted by ubiquitinand proteasome-dependent proteolysis during the G 1 -to-Sphase transition (4,5,33,35). In the frog, Xenopus laevis, three types of CDK inhibitors have been identified that share sequence and functional similarities with mammalian p27 and p21. The first type of CDK inhibitor includes the Xenopus inhibitor of CDK (p27 Xic1 or Xic1) and kinase inhibitor from Xenopus (p28 Kix1 or Kix1), which share ϳ90% amino acid sequence identity with each other, preferentially inhibit the activity of CDK2-cyclin E or A and bind all CDK-cyclins and proliferating cell nuclear antigen (PCNAs) (30, 32). The second and third types of Xenopus CDK inhibitors are p16 Xic2 and p17Xic3 , which sh...

E2F1 is a eukaryotic transcription factor that is known to regulate various cellular pathways such as cell cycle progression, DNA replication, DNA damage responses and induction of apoptosis. Given its versatile roles, a precise and tight regulation of E2F1 is very critical to maintain genomic stability. E2F1 is regulated both at transcriptional and posttranslational levels during cell cycle and upon DNA damage. After S phase, E2F1 is targeted for degradation and is kept at low levels or in an inactive state until the next G 1/S phase transition. Our studies show that APC/C ubiquitin ligase in conjunction with its co-activator Cdh1 (APC/C (Cdh1) ) can downregulate E2F1. We also identify an APC/C subunit APC5 that binds to E2F1 and is essential for E2F1 ubiquitination. We confirm an interaction between E2F1 and Cdh1 as well as an interaction between E2F1 and APC5 both in vivo and in vitro. In vitro GST pull-down assays have mapped the C-terminal 79 a.a. of E2F1 as Cdh1 interacting residues. Ectopically expressed Cdh1 downregulates the expression of E2F1-4. Our studies have also shown for the first time that E2F1 can be modified by K11-linkage specific ubiquitin chain formation (Ub-K11). The formation of Ub-K11 chains on E2F1 is increased in the presence of Cdh1 and accumulated in the presence of proteasome inhibitor, suggesting that APC/C (Cdh1) targets E2F1 for degradation by forming Ub-K11 chains. We also show that the effect of Cdh1 on E2F1 degradation is blocked upon DNA damage. Interestingly, Ub-K11-linked E2F1 accumulates after treatment of DNA damaging agents. The data suggest that DNA damage signaling processes do not inhibit APC/C (Cdh1) to ubiquitinate E2F1. Instead, they block the proteasomal degradation of Ub-K11-linked E2F1, and therefore lead to its accumulation.

DNA replication is a highly conserved process that accurately copies the genetic information from one generation to the next. The processes of chromatin disassembly and reassembly during DNA replication also have to be precisely regulated to ensure that the genetic material is compactly packaged to fit into the nucleus while also maintaining the epigenetic information that is carried by the histone proteins bound to the DNA, through cell divisions. Half of the histones that are deposited during replication are from the parental chromatin and carry the parental epigenetic information, while the other half of the histones are newly-synthesized. It has been of growing interest to understand how the parental pattern of epigenetic marks is re-established on the newly-synthesized histones, in a DNA sequence-specific manner, in order to maintain the epigenetic information through cell divisions. In this review we will discuss how histone chaperone proteins precisely coordinate the chromatin assembly process during DNA replication. We also discuss the recent evidence that histone-modifying enzymes, rather than the parental histones, are themselves epigenetic factors that remain associated with the DNA through replication to re-establish the epigenetic information on the newly-assembled chromatin.