Tumor suppressor p53 is activated by several stimuli, including DNA damage and oncogenic stress. Previous studies (Takaoka, A., S. Hayakawa, H. Yanai, D. Stoiber, H. Negishi, H. Kikuchi, S. Sasaki, K. Imai, T. Shibue, K. Honda, and T. Taniguchi. 2003. Nature. 424:516–523) have shown that p53 is also induced in response to viral infections as a downstream transcriptional target of type I interferon (IFN) signaling. Moreover, many viruses, including SV40, human papillomavirus, Kaposi's sarcoma herpesvirus, adenoviruses, and even RNA viruses such as polioviruses, have evolved mechanisms designated to abrogate p53 responses. We describe a novel p53 function in the activation of the IFN pathway. We observed that infected mouse and human cells with functional p53 exhibited markedly decreased viral replication early after infection. This early inhibition of viral replication was mediated both in vitro and in vivo by a p53-dependent enhancement of IFN signaling, specifically the induction of genes containing IFN-stimulated response elements. Of note, p53 also contributed to an increase in IFN release from infected cells. We established that this p53-dependent enhancement of IFN signaling is dependent to a great extent on the ability of p53 to activate the transcription of IFN regulatory factor 9, a central component of the IFN-stimulated gene factor 3 complex. Our results demonstrate that p53 contributes to innate immunity by enhancing IFN-dependent antiviral activity independent of its functions as a proapoptotic and tumor suppressor gene.

The success of targeting kinases in cancer with small molecule inhibitors has been tempered by the emergence of drug-resistant kinase domain mutations. In patients with chronic myeloid leukemia treated with ABL inhibitors, BCR-ABL kinase domain mutations are the principal mechanism of relapse. Certain mutations are occasionally detected before treatment, suggesting increased fitness relative to wild-type p210 BCR-ABL. We evaluated the oncogenicity of eight kinase inhibitor-resistant BCR-ABL mutants and found a spectrum of potencies greater or less than p210. Although most fitness alterations correlate with changes in kinase activity, this is not the case with the T315I BCR-ABL mutation that confers clinical resistance to all currently approved ABL kinase inhibitors. Through global phosphoproteome analysis, we identified a unique phosphosubstrate signature associated with each drug-resistant allele, including a shift in phosphorylation of two tyrosines (Tyr 253 and Tyr 257 ) in the ATP binding loop (P-loop) of BCR-ABL when Thr 315 is Ile or Ala. Mutational analysis of these tyrosines in the context of Thr 315 mutations demonstrates that the identity of the gatekeeper residue impacts oncogenicity by altered P-loop phosphorylation. Therefore, mutations that confer clinical resistance to kinase inhibitors can substantially alter kinase function and confer novel biological properties that may impact disease progression.chronic myelogenous leukemia ͉ kinase inhibitor resistance ͉ phosphoproteomics ͉ imatinib ͉ dasatinib P oint mutations in the kinase domain of BCR-ABL are primarily responsible for resistance to the ABL inhibitor imatinib (Gleevec) in chronic myelogenous leukemia (CML) patients. The majority of imatinib-resistant BCR-ABL point mutations (of Ͼ50 distinct examples now reported clinically) impair drug binding by restricting flexibility of the enzyme, precluding adoption of the inactive conformation required for imatinib binding (1-4). The second generation Abl inhibitor dasatinib is effective against imatinib-resistant CML because it binds the BCR-ABL kinase domain regardless of activation loop conformation (5-7). As a result, the number of BCR-ABL mutations capable of conferring resistance to dasatinib is small and is limited almost exclusively to direct contact sites (8, 9). One mutation, T315I, confers resistance to imatinib, dasatinib, and the imatinib-related compound nilotinib (AMN-107) (10, 11).Although discovered in the context of drug resistance, there is growing evidence that these mutations may confer other fitness advantages to BCR-ABL. First, the T315I and E255K mutants were each detected by our group in imatinib-naïve CML blast crisis patients by direct sequencing of total BCR-ABL cDNA and are therefore estimated to account for at least 20% of the CML tumor burden in these patients (1). In addition, these and other kinase domain mutations have been identified before treatment in CML patients using mutation-specific quantitative PCR (12-18). Furthermore, the analogous mutation to T315I in the...

Acute lymphoblastic leukemia (ALL) is the most common childhood malignancy, and implementation of risk-adapted therapy has been instrumental in the dramatic improvements in clinical outcomes. A key to risk-adapted therapies includes the identification of genomic features of individual tumors, including chromosome number (for hyper- and hypodiploidy) and gene fusions, notably ETV6-RUNX1, TCF3-PBX1, and BCR-ABL1 in B-cell ALL (B-ALL). RNA-sequencing (RNA-seq) of large ALL cohorts has expanded the number of recurrent gene fusions recognized as drivers in ALL, and identification of these new entities will contribute to refining ALL risk stratification. We used RNA-seq on 126 ALL patients from our clinical service to test the utility of including RNA-seq in standard-of-care diagnostic pipelines to detect gene rearrangements and IKZF1 deletions. RNA-seq identified 86% of rearrangements detected by standard-of-care diagnostics. KMT2A (MLL) rearrangements, although usually identified, were the most commonly missed by RNA-seq as a result of low expression. RNA-seq identified rearrangements that were not detected by standard-of-care testing in 9 patients. These were found in patients who were not classifiable using standard molecular assessment. We developed an approach to detect the most common IKZF1 deletion from RNA-seq data and validated this using an RQ-PCR assay. We applied an expression classifier to identify Philadelphia chromosome–like B-ALL patients. T-ALL proved a rich source of novel gene fusions, which have clinical implications or provide insights into disease biology. Our experience shows that RNA-seq can be implemented within an individual clinical service to enhance the current molecular diagnostic risk classification of ALL.

An abundance of evidence exists that shows calcium channel blockade promotes injury in cultured neurons. However, few studies have addressed the in vivo toxicity of such agents. We now show that the L-type calcium channel antagonist nimodipine promotes widespread and robust injury throughout the neonatal rat brain, in an age-dependent manner. Using both isolated neuronal as well as brain slice approaches, we address mechanisms behind such injury. These expanded studies show a consistent pattern of injury using a variety of agents that lower intracellular calcium. Collectively, these observations indicate that postnatal brain development represents a transitional period for still developing neurons, from being highly sensitive to reductions in intracellular calcium to being less vulnerable to such changes. These observations directly relate to current therapeutic strategies targeting neonatal brain injury.

The effect of ERK, p38, and JNK signaling on p53-dependent apoptosis and cell cycle arrest was investigated using a Friend murine erythroleukemia virus (FVP)-transformed cell line that expresses a temperature-sensitive p53 allele, DP16.1/p53ts. In response to p53 activation at 32°C, DP16.1/p53ts cells undergo p53-dependent G 1 cell cycle arrest and apoptosis. As a result of viral transformation, these cells express the spleen focus forming env-related glycoprotein gp55, which can bind to the erythropoietin receptor (EPO-R) and mimics many aspects of EPO-induced EPO-R signaling. We demonstrate that ERK, p38 and JNK mitogen-activated protein kinases (MAPKs) are constitutively active in DP16.1/p53ts cells. Constitutive MEK activity contributes to p53-dependent apoptosis and phosphorylation of p53 on serine residue 15. The pro-apoptotic effect of this MAPK kinase signal likely reflects an aberrant Ras proliferative signal arising from FVP-induced viral transformation. Inhibition of MEK alters the p53-dependent cellular response of DP16.1/p53ts from apoptosis to G 1 cell cycle arrest, with a concomitant increase in p21 WAF1 , suggesting that the Ras/MEK pathway may influence the cellular response to p53 activation. p38 and JNK activity in DP16.1/p53ts cells is anti-apoptotic and capable of limiting p53-dependent apoptosis at 32°C. Moreover, JNK facilitates p53 protein turnover, which could account for the enhanced apoptotic effects of inhibiting this MAPK pathway in DP16.1/p53ts cells. Overall, these data show that intrinsic MAPK signaling pathways, active in transformed cells, can both positively and negatively influence p53-dependent apoptosis, and illustrate their potential to affect cancer therapies aimed at reconstituting or activating p53 function.The p53 tumor suppressor protein is activated in response to DNA damage and abnormal proliferative signals and can induce apoptosis through the activation of death-promoting gene targets (e.g. Bax, p53AIP1, Pidd/Lrdd, Puma, and Noxa), and cell cycle arrest through the activation of p21 WAF1 , GADD45,. Apoptosis and arrest are believed to be important mechanisms of p53 tumor suppression, and are capable of preventing the expansion of cancer-prone cells (e.g. harboring mutations and/or under the influence of inappropriate growth signals). The factors and mechanisms underlying the decision to undergo apoptosis or growth arrest in response to p53 are not fully understood. This decision is likely complex and governed by multiple factors that depend on extrinsic factors (e.g. the presence of soluble growth factors) and intrinsic factors (e.g. hyperactive survival signaling pathways, defective death-signaling pathways) that are additionally cell type-specific.We and others have shown that p53-induced apoptosis in hematopoietic cells can be suppressed in the presence of cytokines or mitogenic factors such as phorbol 12-myristate 13-acetate and that cells remain in a viable growth-arrested state (2-7). Survival pathways, commonly activated in transformed cells independently of...