High-throughput screening of the Saccharomyces cerevisiae genome for 2-amino-3-methylimidazo [4,5-f] quinoline resistance identifies colon cancer-associated genes.

Heterocyclic aromatic amines (HAAs) are potent carcinogenic agents found in charred meats and cigarette smoke. However, few eukaryotic resistance genes have been identified. We used Saccharomyces cerevisiae (budding yeast) to identify genes that confer resistance to 2-amino-3-methylimidazo[4,5-f] quinoline (IQ). CYP1A2 and NAT2 activate IQ to become a mutagenic nitrenium compound. Deletion libraries expressing human CYP1A2 and NAT2 or no human genes were exposed to either 400 or 800 µM IQ for 5 or 10 generations. DNA barcodes were sequenced using the Illumina HiSeq 2500 platform and statistical significance was determined for exactly matched barcodes. We identified 424 ORFs, including 337 genes of known function, in duplicate screens of the "humanized" collection for IQ resistance; resistance was further validated for a select group of 51 genes by growth curves, competitive growth, or trypan blue assays. Screens of the library not expressing human genes identified 143 ORFs conferring resistance to IQ per se. Ribosomal protein and protein modification genes were identified as IQ resistance genes in both the original and "humanized" libraries, while nitrogen metabolism, DNA repair, and growth control genes were also prominent in the "humanized" library. Protein complexes identified included the casein kinase 2 (CK2) and histone chaperone (HIR) complex. Among DNA Repair and checkpoint genes, we identified those that function in postreplication repair (RAD18, UBC13, REV7), base excision repair (NTG1), and checkpoint signaling (CHK1, PSY2). These studies underscore the role of ribosomal protein genes in conferring IQ resistance, and illuminate DNA repair pathways for conferring resistance to activated IQ.

Genome Profiling for Aflatoxin B1 Resistance in Saccharomyces cerevisiae Reveals a Role for the CSM2/SHU Complex in Tolerance of Aflatoxin B1-Associated DNA Damage.

Exposure to the mycotoxin aflatoxin B1 (AFB1) strongly correlates with hepatocellular carcinoma (HCC). P450 enzymes convert AFB1 into a highly reactive epoxide that forms unstable 8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 (AFB1-N7-Gua) DNA adducts, which convert to stable mutagenic AFB1 formamidopyrimidine (FAPY) DNA adducts. In CYP1A2-expressing budding yeast, AFB1 is a weak mutagen but a potent recombinagen. However, few genes have been identified that confer AFB1 resistance. Here, we profiled the yeast genome for AFB1 resistance. We introduced the human CYP1A2 into ∼90% of the diploid deletion library, and pooled samples from CYP1A2-expressing libraries and the original library were exposed to 50 µM AFB1 for 20 hs. By using next generation sequencing (NGS) to count molecular barcodes, we initially identified 86 genes from the CYP1A2-expressing libraries, of which 79 were confirmed to confer AFB1 resistance. While functionally diverse genes, including those that function in proteolysis, actin reorganization, and tRNA modification, were identified, those that function in postreplication DNA repair and encode proteins that bind to DNA damage were over-represented, compared to the yeast genome, at large. DNA metabolism genes also included those functioning in checkpoint recovery and replication fork maintenance, emphasizing the potency of the mycotoxin to trigger replication stress. Among genes involved in postreplication repair, we observed that CSM2, a member of the CSM2(SHU) complex, functioned in AFB1-associated sister chromatid recombination while suppressing AFB1-associated mutations. These studies thus broaden the number of AFB1 resistance genes and have elucidated a mechanism of error-free bypass of AFB1-associated DNA adducts.

A model for the development of mothers' perceived vulnerability of preterm infants.

OBJECTIVE: Some mothers of preterm infants continue to view them as vulnerable after their health has improved. These exaggerated perceptions of vulnerability lead to poor parent-child interactions and, subsequently, to adverse child outcomes. However, there is no theoretical model to explain why these exaggerated perceptions develop in only some mother-child dyads. METHOD: Data for this study come from a randomized trial of an intervention to reduce distress in mothers of preterm infants. A total of 105 mothers older than 18 years of infants aged 25-34 weeks, weighing >600 g and with clinically significant anxiety, depression, or trauma symptoms, were recruited and randomized. Women were assessed at baseline, after intervention, and at 6 months after birth. The outcome for these analyses was perceptions of infant vulnerability as measured by the Vulnerable Baby Scale (VBS) at 6 months after birth. A theoretical model developed from the extant literature was tested using the MacArthur Mediator-Moderator Approach. RESULTS: A dysfunctional coping style, high depression, anxiety, or trauma symptoms in response to the preterm birth, and low social support were related to 6-month VBS scores. Maternal response to trauma was directly related to VBS, and an important precursor of maternal response to trauma was a dysfunctional coping style. CONCLUSIONS: This model suggests that maternal responses to trauma are critical in the formation of exaggerated perceptions of vulnerability as are dysfunctional coping styles and low social support. Women with these characteristics should be targeted for intervention to prevent poor parenting practices that result from exaggerated perceptions of vulnerability.

Does an intervention to reduce maternal anxiety, depression and trauma also improve mothers' perceptions of their preterm infants' vulnerability?

To determine if an intervention to reduce maternal distress and address maternal perceptions of infants' vulnerability also reduces perceptions of vulnerability, 105 mothers of premature infants (25- to 34-weeks' gestational age; >600 g) with depression, anxiety, or trauma were randomized to a six- or nine-session intervention or a comparison condition. The outcome was changes in a measure of perception of infant vulnerability between 4 to 5 weeks' and 6 months' postdelivery, the Vulnerability Baby Scale (VBS; B. Forsyth, S. Horwitz, J. Leventhal, & J. Burger, 1996; N. Kerruish, K. Settle, P. Campbell-Stokes, & B. Taylor, 2005). High scores on the VBS were indicative of high levels of perceived infant vulnerability. The perceptions of infants' vulnerability showed significant declines, with no differences across groups or in rate of change. Mothers reporting prior trauma at entry to the study showed much lower perceptions of infants' vulnerability scores under the intervention, Cohen's d = -0.86, p = .01. Given that women with prior trauma are very likely to view their premature infants as vulnerable, this intervention may have important implications for subsequent parenting behaviors and child development.

Prevention of traumatic stress in mothers of preterms: 6-month outcomes.

OBJECTIVE: Symptoms of posttraumatic stress disorder are a well-recognized phenomenon in mothers of preterm infants, with implications for maternal health and infant outcomes. This randomized controlled trial evaluated 6-month outcomes from a skills-based intervention developed to reduce symptoms of posttraumatic stress disorder, anxiety, and depression. METHODS: One hundred five mothers of preterm infants were randomly assigned to (1) a 6- or 9-session intervention based on principles of trauma-focused cognitive behavior therapy with infant redefinition or (2) a 1-session active comparison intervention based on education about the NICU and parenting of the premature infant. Outcome measures included the Davidson Trauma Scale, the Beck Depression Inventory II, and the Beck Anxiety Inventory. Participants were assessed at baseline, 4 to 5 weeks after birth, and 6 months after the birth of the infant. RESULTS: At the 6-month assessment, the differences between the intervention and comparison condition were all significant and sizable and became more pronounced when compared with the 4- to 5-week outcomes: Davidson Trauma Scale (Cohen's d = -0.74, P < .001), Beck Anxiety Inventory (Cohen's d = -0.627, P = .001), Beck Depression Inventory II (Cohen's d = -0.638, P = .002). However, there were no differences in the effect sizes between the 6- and 9-session interventions. CONCLUSIONS: A brief 6-session intervention based on principles of trauma-focused cognitive behavior therapy was effective at reducing symptoms of trauma, anxiety, and depression in mothers of preterm infants. Mothers showed increased benefits at the 6-month follow-up, suggesting that they continue to make use of techniques acquired during the intervention phase.

Prevention of traumatic stress in mothers with preterm infants: a randomized controlled trial.

OBJECTIVE: The current study evaluates a treatment intervention developed with the goal of reducing symptoms of posttraumatic stress, depression, and anxiety in parents of premature infants. METHODS: A total of 105 mothers of preterm infants (25-34 weeks' gestational age; >600 g) were randomized to receive a 6-session intervention developed to target parental trauma as well as facilitate infant redefinition (n = 62) or to an active comparison group (n = 43). Mothers in the intervention group received a combination of trauma-focused treatments, including psychoeducation, cognitive restructuring, progressive muscle relaxation, and development of their trauma narrative. The intervention also incorporated material targeting infant redefinition, defined as the process of changing the mother's negative perceptions of her infant and the parenting experience. RESULTS: Mothers in the intervention group reported a greater reduction in both trauma symptoms (Cohen's d = 0.41, P = .023) and depression (Cohen's d = 0.59, P < .001) compared with the comparison group. Patients under both conditions improved significantly in terms of anxiety, with no differences between groups. Results of the moderator analysis showed that mothers with higher ratings of baseline NICU stress benefited more from the intervention compared with mothers who had lower ratings (P = .036). CONCLUSIONS: This short, highly manualized intervention for mothers of preterm infants statistically significantly reduced symptoms of trauma and depression. The intervention is feasible, can be delivered with fidelity, and has high ratings of maternal satisfaction. Given that improvements in mothers' distress may lead to improved infant outcomes, this intervention has the potential for a high public health impact.