Individuals with Li-Fraumeni syndrome carry inherited mutations in the p53 tumor suppressor gene and are predisposed to tumor development. To examine the mechanistic nature of these p53 missense mutations, we generated mice harboring a G-to-A substitution at nucleotide 515 of p53 (p53+/515A) corresponding to the p53R175H hot spot mutation in human cancers. Although p53+/515A mice display a similar tumor spectrum and survival curve as p53+/- mice, tumors from p53+/515A mice metastasized with high frequency. Correspondingly, the embryonic fibroblasts from the p53515A/515A mutant mice displayed enhanced cell proliferation, DNA synthesis, and transformation potential. The disruption of p63 and p73 in p53-/- cells increased transformation capacity and reinitiated DNA synthesis to levels observed in p53515A/515A cells. Additionally, p63 and p73 were functionally inactivated in p53515A cells. These results provide in vivo validation for the gain-of-function properties of certain p53 missense mutations and suggest a mechanistic basis for these phenotypes.

Disinhibition among alcoholics may precede or result from alcohol use disorders (AUDs). It remains unclear how disinhibition might contribute to AUD risk among youths with a family history of alcoholism (FHP). We used functional magnetic resonance imaging (fMRI) to explore inhibition-related neural risk factors for AUD. Participants were 12- to 14-year-old nondrinkers, including 12 FHP youths and 14 youths with no family history of alcoholism (FHN). Youths performed a go/no-go task during fMRI acquisition. At a conservative threshold, FHN youths showed less inhibitory response than FHP youths in the left middle frontal gyrus, despite similar task performance between groups. Using a more liberal threshold, FHP youths also demonstrated less response in additional frontal regions. These preliminary findings suggest that FHP youths show less inhibitory frontal response than FHN youths. Altered neural activation among FHP youths may underlie subsequent disinhibition and could be related to the AUD risk.

No abstract

The tumor suppressor protein p53 is a transcription factor that induces G 1 arrest of the cell cycle and/or apoptosis. The murine double-minute protein MDM2 and its homologue MDM4 (also known as MDMX) are critical regulators of p53. Altered transcripts of the human homologue of mdm2, MDM2, have been identified in human tumors, such as invasive carcinoma of the breast, lung carcinoma, and liposarcoma. MDM2 alternate forms act to negatively regulate the normal MDM2 gene product, thus activating p53. Although many reports have documented a plethora of tumor types characterized by MDM2 alternative transcripts, few have investigated the signals that might initiate alternative splicing. We have identified a novel role of these alternative MDM2 transcripts in the normal surveillance mechanism of the cell and in DNA damage response. We report that alternate forms of MDM2 are detected after UV irradiation. Furthermore, we show that mouse cells treated with UV are also characterized by alternative transcripts of mdm2, suggesting that this is an important and evolutionarily conserved mechanism for regulating the expression of MDM2/mdm2. An additional p53 regulator and mdm2 family member, MDM4, is likewise alternatively spliced following UV irradiation. By activating alternative splicing of both MDM2 and MDM4, yet another layer of p53 regulation is initiated by the cells in response to damage. A stepwise model for malignant conversion by which alternate forms of MDM2 and MDM4 place selective pressure on the cells to acquire additional alterations in the p53 pathway is herein proposed. (Cancer Res 2006; 66(19): 9502-8)

Adolescent alcohol involvement may affect male and female brains differently, and adolescent females may be somewhat more vulnerable to adverse alcohol effects. With continued drinking, these adolescents may be at an increased risk for behavioural deficits.

Mdm2 inhibits the function of the p53 tumor suppressor. Mdm2 is overexpressed in many tumors with wild-type p53 suggesting an alternate mechanism of loss of p53 activity in tumors. An Mdm2-binding protein (MTBP) was identified using a yeast two-hybrid screen. In tissue culture, MTBP inhibits Mdm2 self-ubiquitination, leading to stabilization of Mdm2 and increased degradation of p53. To address the role of MTBP in the regulation of the p53 pathway in vivo, we deleted the Mtbp gene in mice. Homozygous disruption of Mtbp resulted in early embryonic lethality, which was not rescued by loss of p53. Mtbp þ /À mice were not tumor prone. When mice were sensitized for tumor development by p53 heterozygosity, we found that the Mtbp þ /À p53 Introduction p53 is a transcription factor that activates numerous downstream genes with roles in cell cycle arrest, apoptosis, DNA repair and senescence (Levine et al., 2004). As such, disruption of the p53 pathway is a critical event in human cancer. Mutations or deletions in the p53 gene occur in approximately 50% of cancers (Bartek et al., 1991;Levine, 1993;Vogelstein et al., 2000). The p53 pathway is also inactivated by overexpression of the p53 inhibitor, Mdm2. Overexpression of Mdm2 by several mechanisms occurs in about 30% of sarcomas and many other types of tumors (Iwakuma and Lozano, 2003). ARF (alternative reading frame of the Ink 4a locus), another important regulator of this pathway, binds and inhibits Mdm2 by relocating Mdm2 from nucleus to nucleolus (Sharpless and DePinho, 1999;Weber et al., 1999). Therefore, ARF loss in tumors releases Mdm2, leading to increased binding to and inactivation of p53. Thus, the ARF-Mdm2-p53 pathway is a key pathway that must be bypassed in tumor development.Experiments using genetically engineered mice have provided direct evidence for the importance of these factors in tumorigenesis. Mice with homozygous or heterozygous deletion of p53 develop tumors (Donehower et al., 1992;Tsukada et al., 1993;Jacks et al., 1994;Purdie et al., 1994). Mice with missense mutations identical to those found in humans with Li-Fraumeni syndrome develop a variety of tumors with frequent metastasis (Lang et al., 2004;Olive et al., 2004 MTBP was isolated as a novel Mdm2-binding protein (Boyd et al., 2000). The MTBP-Mdm2 interaction was observed using purified proteins in vitro and by overexpression in cells. Overexpression of MTBP protects Mdm2 from self-ubiquitination, leading to Mdm2 stabilization and p53 degradation (Brady et al., 2005). We therefore hypothesized that MTBP affects tumor development through modulation of p53 activity. To test this hypothesis and examine the in vivo physiological function of MTBP, we generated mice with disruption of the Mtbp gene. Our results show that Mtbp-null mice were embryonic lethal, and this phenotype was p53 independent. Mtbp þ /À mice were normal, but when crossed with p53 þ /À mice, Mtbpþ /À mice developed significantly more metastatic tumors compared to p53 þ /À mice. In vitro invasion assays clearly supported the in ...

We previously demonstrated that mesenchymal stem/stromal cells (MSC) are recruited to tumors and that IFN-β produced by MSC inhibited tumor growth in xenograft models. Because of a deficient immune system, murine xenograft models cannot fully recapitulate tumor and immune cell interactions during progression. Therefore we investigated the capacity of MSC to migrate to and engraft into primary breast tumor sites and subsequently explore mechanisms of tumor inhibition by MSC-delivered IFN-β in a syngeneic, immunocompetent murine model. Herein we report that 1) systemically administrated MSC migrate to established 4 T1 breast cancer sites and localize among the tumor-stroma border and throughout the tumor mass; 2) high levels of IFN-β secreted by MSC are detectable in the tumor microenvironment but not in circulation; 3) intratumorally produced IFN-β inactivates constitutive phosphorylation of signal transducer activator transcription factor 3 (Stat3), Src, and Akt and down-regulates cMyc and MMP2 expression in 4 T1 cells, and 4) in mice with established breast cancer IFN-β expressing MSC administered systemically resulted in inhibition of primary cancer growth and in dramatic reduction of pulmonary and hepatic metastases. 5) MSC-IFN-β treated, but not control mice, maintained normal levels of splenic mature dendritic (DC), CD8+ T cells and CD4+/Foxp3+ regulatory T-cells (Treg). Our findings suggest that MSC are capable of migrating to tumor sites in an immunocompetent environment, that IFN-β produced by MSC suppresses breast cancer growth through inhibition of Stat3 signaling, and dramatically reduces pulmonary and hepatic metastases.

Childhood obesity is among the leading health concerns in the United States. The relationship between unmet physical activity needs in young children is of particular interest as the trend in childhood obesity continues to rise and unmet physical activity needs are identified. The preschool years are an influential time in promoting healthful lifestyle habits and early childhood interventions may help establish lifelong healthful behaviors which could help prevent obesity later in life. The Food Friends®: Get Movin' with Mighty Moves® is a preschool physical activity program which aims to improve children's gross motor skills and physical activity levels. The home environment and parental modeling are critical factors related to child physical activity in this population. The parent component, Mighty Moves®: Fun Ways to Keep Families Active and Healthy, was designed to address barriers in the home environment that lead to unmet physical activity needs in preschoolers and their families. The program and materials were designed based on Social Marketing tenets and Social Learning Theory principles. Four Colorado Head Start centers were assigned to an experimental group as part of the Mighty Moves® group randomized trial. Quantitative and qualitative evaluation methods were used to determine what messages and materials reached and motivated the target audience to increase physical activity levels. Results of the study indicated the program's materials helped families and children to be more physically active. Additionally, materials and material dissemination were revised to enhance program goals.