Role of AUF1 and HuR in the pH-responsive stabilization of phosphoenolpyruvate carboxykinase mRNA in LLC-PK1-F⁺ cells.

Onset of metabolic acidosis leads to a rapid and pronounced increase in expression of phosphoenolpyruvate carboxykinase (PEPCK) in rat renal proximal convoluted tubules. This adaptive response is modeled by treating a clonal line of porcine LLC-PK(1)-F(+) cells with an acidic medium (pH 6.9, 9 mM HCO(3)(-)). Measurement of the half-lives of PEPCK mRNA in cells treated with normal (pH 7.4, 26 mM HCO(3)(-)) and acidic medium established that the observed increase is due in part to stabilization of the PEPCK mRNA. The pH-responsive stabilization was reproduced in a Tet-responsive chimeric reporter mRNA containing the 3'-UTR of PEPCK mRNA. This response was lost by mutation of a highly conserved AU sequence that binds AUF1 and is the primary element that mediates the rapid turnover of PEPCK mRNA. However, siRNA knockdown of AUF1 had little effect on the basal levels and the pH-responsive increases in PEPCK mRNA and protein. Electrophoretic mobility shift assays established that purified recombinant HuR, another AU element binding protein, also binds with high affinity and specificity to multiple sites within the final 92-nucleotides of the 3'-UTR of the PEPCK mRNA, including the highly conserved AU-rich element. siRNA knockdown of HuR caused pronounced decreases in basal expression and the pH-responsive increases in PEPCK mRNA and protein. Therefore, basal expression and the pH-responsive stabilization of PEPCK mRNA in LLC-PK(1)-F(+) cells, and possibly in the renal proximal tubule, may require the remodeling of HuR and AUF1 binding to the elements that mediate the rapid turnover of PEPCK mRNA.

Does foot placement affect the reliability of static foot posture measurements?

BACKGROUND: Previous studies have reported conflicting results on whether different foot placements in standing can affect static measurements of foot posture. We sought to determine whether three measurements of static foot posture could be consistently measured in three different foot placements while standing. METHODS: Twenty individuals, 12 women and eight men, with a mean age of 24.8 years consented to participate. Two raters assessed the dorsal arch height, midfoot width, and heel width of each foot while the participant stood in the following three foot placements: a standardized placement, a participant-determined placement after marching in place, and a rater-determined foot placement based on observation of the participant's angle of gait and base of support while walking. RESULTS: All three measurements of static foot posture were shown to have high levels of intrarater and interrater reliability. Significant differences in the measurements of dorsal arch height, midfoot width, and heel width were found among all three of the foot placements. There were no differences between the two raters for any of the three measurements of foot posture. CONCLUSIONS: Based on these findings, we recommend that clinicians perform measurements of static foot posture using the same standing foot placement between sessions to ensure a high level of measurement consistency.

The consistency of individual-selected versus rater-determined angle and base of gait.

BACKGROUND: Several studies have reported the necessity of using a standardized foot placement to improve reliability when performing standing foot posture measurements. The intent of this study was to determine whether individuals can reliably place their feet in the same standing position after marching in place or whether the standing position must be determined by a rater observing the angle and base of gait during walking to ensure the consistency of foot placement. METHODS: Twenty individuals (12 women and 8 men; mean age, 24.8 years) consented to participate. All of the participants were asked to march in place for 10 sec and then to stop in their preferred angle and base foot placement. Participants then walked over an 8-m walkway so that one of two raters could observe the participant's angle and base while walking. An angle and base of gait tracing was then made for each participant's foot placement. RESULTS: The two raters and all of the participants demonstrated high levels of reliability for foot placement between the two sessions. The results indicate that asking the participant to march in place provides a more consistent angle and base foot placement between two sessions compared with having a rater determine the angle and base of gait foot placement after observing the participant while walking. CONCLUSIONS: Based on these findings, we recommend using marching in place to position a patient in his or her angle and base foot placement when the measurement or visual assessment of foot posture must be performed for more than one clinical visit.