p53, an important tumor suppressor protein, exerts its function mostly as a sequence-specific transcription factor and is subjected to multiple posttranslational modifications in response to genotoxic stress. Recently, we discovered that lysine methylation of p53 at K372 by Set7/9 (also known as SET7 and Set9) is important for transcriptional activation and stabilization of p53. In this report we provide a molecular mechanism for the effect of p53 methylation on transcription. We demonstrate that Set7/9 activity toward p53, but not the nucleosomal histones, is modulated by DNA damage. Significantly, we show that lysine methylation of p53 is important for its subsequent acetylation, resulting in stabilization of the p53 protein. These p53 modification events can be observed on the promoter of p21 gene, a known transcriptional target of p53. Finally, we show that methylation-acetylation interplay in p53 augments acetylation of histone H4 in the promoter of p21 gene, resulting in its subsequent transcriptional activation and, hence, cell cycle arrest. Collectively, these results suggest that the cross talk between lysine methylation and acetylation is critical for p53 activation in response to DNA damage and that Set7/9 may play an important role in tumor suppression.

VX-680 is a potent inhibitor of Aurora kinases that induces the accumulation of cells with z4N DNA content, followed by cell death. Here, we define the role of p53 and p21Waf1/Cip1 in cell cycle perturbations following exposure to VX-680. Endoreduplication and apoptosis in response to VX-680 are limited in A549 and MCF-7 cells expressing wild-type p53, and markedly enhanced in cells lacking p53, including those engineered to express the HPV16-E6 oncoprotein or short interfering RNA pools targeting p53. In contrast, endoreduplication and apoptosis occur in the p53 wild-type cell lines, RKO and U2OS. The difference in response to VX-680 among these cell lines correlates with the timing of induction of p21Waf1/Cip1 and its ability to inhibit cyclin E-cdk2 activity. In A549 cells, VX-680 induces the expression of p53 and p21Waf1/Cip1 within 24 hours, with consequent inhibition of cyclin E-cdk2, and reduction of retinoblastoma protein phosphorylation, limiting endoreduplication. In RKO and U2OS cells, the induction of p21 Waf1/Cip1 is delayed and associated with higher residual cyclin E-cdk2 kinase activity and retinoblastoma protein phosphorylation, followed by progressive endoreduplication and apoptosis. Abrogation of p21Waf1/Cip1 expression by short interfering RNA targeting in A549 cells results in a substantial increase in the degree of endoreduplication, whereas inducible expression of p21Waf1/Cip1 in p53-negative NCI-H1299 cells inhibits VX-680-induced endoreduplication and cell death. These data suggest that the integrity of the p53-p21Waf1/Cip1 -dependent postmitotic checkpoint governs the response to Aurora kinase inhibition. Although cells with intact checkpoint function arrest with 4N DNA content, those with compromised checkpoint function are more likely to undergo endoreduplication followed by eventual apoptosis. (Cancer Res 2006; 66(15): 7668-77)

Therapeutic monoclonal antibodies and endogenous IgG antibodies show limited uptake into the central nervous system (CNS) due to the blood-brain barrier (BBB), which regulates and controls the selective and specific transport of both exogenous and endogenous materials to the brain. The use of natural transport mechanisms, such as receptor-mediated transcytosis (RMT), to deliver antibody therapeutics into the brain have been studied in rodents and monkeys. Recent successful examples include monovalent bispecific antibodies and mono- or bivalent fusion proteins; however, these formats do not have the capability to bind to both the CNS target and the BBB transport receptor in a bivalent fashion as a canonical antibody would. Dual-variable-domain immunoglobulin (DVD-Ig) proteins offer a bispecific format where monoclonal antibody-like bivalency to both the BBB receptor and the therapeutic target is preserved, enabling independent engineering of binding affinity, potency, valency, epitope and conformation, essential for successful generation of clinical candidates for CNS applications with desired drug-like properties. Each of these parameters can affect the binding and transcytosis ability mediated by different receptors on the brain endothelium differentially, allowing exploration of diverse properties. Here, we describe generation and characterization of several different DVD-Ig proteins, specific for four different CNS targets, capable of crossing the BBB through transcytosis mediated by the transferrin receptor 1 (TfR1). After systemic administration of each DVD-Ig, we used two independent methods in parallel to observe specific uptake into the brain. An electrochemiluminescent-based sensitive quantitative assay and a semi-quantitative immunohistochemistry technique were used for brain concentration determination and biodistribution/localization in brain, respectively. Significantly enhanced brain uptake and retention was observed for all TfR1 DVD-Ig proteins regardless of the CNS target or the systemic administration route selected.

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