👤 Dorothy D Sears

Recreational sedentary screen time (rSST) is the most prevalent form of discretionary sedentary behavior and is strongly linked to poor health outcomes. However, the relationship between time spent in rSST and other 24-h behaviors is not well understood. The purpose of this study was to examine between- and within-day associations between rSST and other 24-h behaviors that include other non-rSST sedentary time (other-SED), standing (STAND), light physical activity (LPA), moderate-to-vigorous physical activity (MVPA), and total sleep (SLEEP). Baseline data from participants randomized to the StandUPTV study, an intervention aimed to reduce rSST in adults, were included. All 24-h behaviors were assessed continuously for 7-days. The activPAL device was used to assess rSST, other-SED, STAND, LPA, and MPVA; SLEEP was assessed using a GENEactiv accelerometer. rSST was collected using Wi-Fi plugs to capture TV time and tablet app usage. A multilevel modelling approach was used to assess bidirectional associations between rSST (total, daytime, evening) and 24-h behaviors at the between-person (across persons) and within-person (across days) levels, adjusting for age, sex, chronotype, education level, and week versus weekend day. The results were scaled hourly for interpretation. On average, 8.0 ± 1.6 days of continuous daily 24-h behavior data were included from 94 participants (age [M ± SD: 42.3 ± 11.5] years; 82% female; 78% White; BMI [M ± SD: 29.8 ± 7.8] kg/m This is the first known analysis of the bidirectional relationship between rSST and 24-h behaviors. The negative association between rSST and other-SED suggests that rSST may displace rather than contribute to more cumulative sedentary time. These findings advocate that contexts of sedentary behavior should be considered as distinct behavioral targets in intervention development. Future interventions targeting rSST reduction should also include strategies to reduce total sedentary time. NCT04464993. Show less

Fatty acids are a vital component of human milk. They influence infant neurodevelopment and immune function, and they provide ∼50% of milk's energy content. The objectives of this study were to characterize the composition of human milk fatty acids in a large Canadian birth cohort and identify factors influencing their variability. In a subset of the CHILD cohort (n = 1094), we analyzed milk fatty acids at 3-4 mo postpartum using GLC. Individual and total SFAs, MUFAs, and n-3 and n-6 PUFAs were analyzed using SD scores and principal component analysis (PCA). Maternal diet, sociodemographic, health, and environmental factors were self-reported. Single-nucleotide polymorphisms were assessed in the fatty acid desaturase 1 (FADS1-rs174556) and 2 (FADS2-rs174575) genes. Fatty acid profiles were variable, with individual fatty acid proportions varying from 2- to >30-fold between women. Using PCA, we identified 4 milk fatty acid patterns: "MUFA and low SFA," "high n-6 PUFA," "high n-3 PUFA," and "high medium-chain fatty acids." In multivariable-adjusted analyses, fish oil supplementation and fatty cold water fish intake were positively associated with DHA and the "high n-3 PUFA" pattern. Mothers carrying the minor allele of FADS1-rs174556 had lower proportions of arachidonic acid (ARA; 20:4n-6). Independent of selected dietary variables and genetic variants, Asian ethnicity was associated with higher linoleic acid (18:2n-6) and total n-3 PUFAs. Ethnic differences in ARA were explained by FADS1 genotype. Maternal obesity was independently associated with higher total SFAs, the "high medium-chain fatty acid" pattern, and lower total MUFAs. Lactation stage, season, study site, and maternal education were also independently associated with some milk fatty acids. No associations were observed for maternal age, parity, delivery mode, or infant sex. This study provides unique insights about the "normal" variation in the composition of human milk fatty acids and the contributing dietary, genetic, sociodemographic, health, and environmental factors. Further research is required to assess implications for infant health. Show less

High expression of the oncoprotein Myc has been linked to poor outcome in human tumors. Although MYC gene amplification and translocations have been observed, this can explain Myc overexpression in only a subset of human tumors. Myc expression is in part controlled by its protein stability, which can be regulated by phosphorylation at threonine 58 (T58) and serine 62 (S62). We now report that Myc protein stability is increased in a number of breast cancer cell lines and this correlates with increased phosphorylation at S62 and decreased phosphorylation at T58. Moreover, we find this same shift in phosphorylation in primary breast cancers. The signaling cascade that controls phosphorylation at T58 and S62 is coordinated by the scaffold protein Axin1. We therefore examined Axin1 in breast cancer and report decreased AXIN1 expression and a shift in the ratio of expression of two naturally occurring AXIN1 splice variants. We demonstrate that this contributes to increased Myc protein stability, altered phosphorylation at S62 and T58, and increased oncogenic activity of Myc in breast cancer. Thus, our results reveal an important mode of Myc activation in human breast cancer and a mechanism contributing to Myc deregulation involving unique insight into inactivation of the Axin1 tumor suppressor in breast cancer. Show less

Expression of the c-Myc proto-oncoprotein is tightly regulated in normal cells. Phosphorylation at two conserved residues, threonine58 (T58) and serine62 (S62), regulates c-Myc protein stability. In cancer cells, c-Myc can become aberrantly stabilized associated with altered T58 and S62 phosphorylation. A complex signalling cascade involving GSK3beta kinase, the Pin1 prolyl isomerase, and the PP2A-B56alpha phosphatase controls phosphorylation at these sites. We report here a novel role for the tumour suppressor scaffold protein Axin1 in facilitating the formation of a degradation complex for c-Myc containing GSK3beta, Pin1, and PP2A-B56alpha. Although knockdown of Axin1 decreases the association of c-Myc with these proteins, reduces T58 and enhances S62 phosphorylation, and increases c-Myc stability, acute expression of Axin1 reduces c-Myc levels and suppresses c-Myc transcriptional activity. Moreover, the regulation of c-Myc by Axin1 is impaired in several tested cancer cell lines with known stabilization of c-Myc or loss of Axin1. This study provides critical insight into the regulation of c-Myc expression, how this can be disrupted in three cancer types, and adds to our knowledge of the tumour suppressor activity of Axin1. Show less