MAGE-A cancer/testis antigens inhibit MDM2 ubiquitylation function and promote increased levels of MDM4

Melanoma antigen A (MAGE-A) proteins comprise a structurally and biochemically similar sub-family of Cancer/Testis antigens that are expressed in many cancer types and are thought to contribute actively to malignancy. MAGE-A proteins are established regulators of certain cancer-associated transcription factors, including p53, and are activators of several RING finger-dependent ubiquitin E3 ligases. Here, we show that MAGE-A2 associates with MDM2, a ubiquitin E3 ligase that mediates ubiquitylation of more than 20 substrates including mainly p53, MDM2 itself, and MDM4, a potent p53 inhibitor and MDM2 partner that is structurally related to MDM2. We find that MAGE-A2 interacts with MDM2 via the N-terminal p53-binding pocket and the RING finger domain of MDM2 that is required for homo/hetero-dimerization and for E2 ligase interaction. Consistent with these data, we show that MAGE-A2 is a potent inhibitor of the E3 ubiquitin ligase activity of MDM2, yet it does not have any significant effect on p53 turnover mediated by MDM2. Strikingly, however, increased MAGE-A2 expression leads to reduced ubiquitylation and increased levels of MDM4. Similarly, silencing of endogenous MAGE-A expression diminishes MDM4 levels in a manner that can be rescued by the proteasomal inhibitor, bortezomid, and permits increased MDM2/MDM4 association. These data suggest that MAGE-A proteins can: (i) uncouple the ubiquitin ligase and degradation functions of MDM2; (ii) act as potent inhibitors of E3 ligase function; and (iii) regulate the turnover of MDM4. We also find an association between the presence of MAGE-A and increased MDM4 levels in primary breast cancer, suggesting that MAGE-A-dependent control of MDM4 levels has relevance to cancer clinically

Activation During Observed Parent–Child Interactions with Anxious Youths: A Pilot Study

Parent–child interaction paradigms are often used to observe dysfunctional family processes; however, the influence of such tasks on a participant’s level of activation remain unclear. The aim of this pilot project is to explore the stimulus value of interaction paradigms that have been commonly used in child anxiety research. Twenty-nine parent–child dyads with clinically anxious (n = 16) and non-anxious (n = 13) youths engaged in a series of tasks (threat and non-threat) used in previous studies of parenting and youth anxiety. Heart rate (HR) data, as an indicator of physiological activation, were collected across tasks, and participants rated the perceived representativeness of their interactions in the laboratory to their usual behavior at home. Significant HR changes were observed for both parent and child. Change in child HR from baseline to non-threat task was smaller than change in HR from baseline to threat tasks. Change in parent HR from baseline to ambiguous situations tasks was smaller than changes from baseline to other threat tasks. Differences in HR change between anxious and non-anxious children were explored. Participants rated laboratory interactions as similar to those experienced in the home. Results suggest that presumably emotionally-charged discussion tasks may produce increased activation compared to tasks that were designed to be more neutral. Implications for future research and limitations are discussed

Reactive oxygen species in phagocytic leukocytes

Phagocytic leukocytes consume oxygen and generate reactive oxygen species in response to appropriate stimuli. The phagocyte NADPH oxidase, a multiprotein complex, existing in the dissociated state in resting cells becomes assembled into the functional oxidase complex upon stimulation and then generates superoxide anions. Biochemical aspects of the NADPH oxidase are briefly discussed in this review; however, the major focus relates to the contributions of various modes of microscopy to our understanding of the NADPH oxidase and the cell biology of phagocytic leukocytes

Mitochondria, hydrogenosomes and mitosomes: products of evolutionary tinkering!

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