Protein synthesis rates are commonly measured by using isotopic tracers to quantify the VX-770 incorporation of a labelled amino acid into muscle proteins. SUnSET technique and then describe our SUnSET methodology and the evidence that supports the validity and accuracy of this technique for measuring skeletal muscle protein synthesis For many years puromycin has been an important tool in molecular biology by acting as a selection agent for cultured cells that express the enzyme puromycin-N-acetyl-transferase (33). Importantly puromycin is a structural analogue of aminoacyl-transfer RNA (aminoacyl-tRNA; specifically tyrosyl-tRNA; Figure 1A) and as such can be incorporated into elongating peptide chains via the formation of a peptide bond (23). However whereas aminoacyl-tRNAs VX-770 contain a hydrolyzable ester bond between their tRNA ribose moiety and the attached amino acid molecule puromycin has a non-hydrolyzable amide bond in the equivalent position (Figure 1A). Thus the binding of puromycin to a growing peptide chain prevents a new peptide bond from being formed with the next aminoacyl-tRNA. As a consequence puromycin binding results in the termination of peptide elongation and leads to the release of the truncated puromycin bound peptide from the ribosome (Figure 1B) (34). At very high concentrations puromycin effectively shuts down the elongation phase of translation and thus inhibit protein synthesis (35); however at very low concentrations that do not inhibit the overall rate of translation the rate at which puromycin-labelled peptides are formed reflects the overall rate of protein synthesis (29). This later property makes puromycin a potential tool for the measurement of changes in protein synthesis rates. Indeed Nakano and Hara (1979) were the first to investigate the use of 3H-puromycin to measure changes in protein synthesis rates and demonstrated that puromycin could be used to effectively detect starvation- and low protein diet-induced decreases in protein synthesis rates in whole tissues including skeletal muscle (22). However it took another 30 years with the development of the SUnSET technique (29) to renew interest in the use of puromycin for detecting changes in protein synthesis. Figure 1 Puromycin structure and mechanism of action SUnSET The SUnSET or SUrface SEnsing of Translation technique specifically involves the use of an anti-puromycin antibody for the immunological detection Rabbit Polyclonal to Chk2 (phospho-Thr68). of puromycin-labelled VX-770 peptides (29). Originally developed for use in cultured cells SUnSET allows for the detection of changes in protein synthesis in whole cell lysates using western blotting (WB) in multiple live cells using fluorescence-activated cell sorting (FACS) and at the single cell level with immunohistochemistry (IHC) (29). SUnSET in cell culture has been shown to have a similar dynamic range as protein synthesis measurements performed using 35S-methionine. VX-770 Furthermore the dose of puromycin used in these cell culture studies (up to 18.4 μM) was shown to not interfere with the overall rate of protein synthesis (29). Importantly SUnSET is able to detect increases and decreases in protein synthesis that are essentially indistinguishable from those obtained using 35S-methionine (29). Thus SUnSET has been shown to be a valid alternative to the use of radioisotopes for measuring changes in protein synthesis in cell culture and provides a clear advantage in allowing for the visualization of protein synthesis at the single cell level (13 29 Using SUnSET to Measure Changes in Skeletal Muscle Protein Synthesis Due to our ongoing interest in the regulation of skeletal muscle mass and specifically the role of the mammalian target of rapamycin (mTOR) in regulating protein synthesis and muscle hypertrophy (8 15 we were very interested in determining if SUnSET could be used to detect changes in protein synthesis in whole skeletal muscles under conditions. Thus to investigate the validity and accuracy of the SUnSET technique we performed a number of experiments using WB and IHC to measure changes in protein synthesis rates at the whole muscle and single muscle fiber levels (10). Western Blot SUnSET First we set out to determine whether the VX-770 WB version of SUnSET (WB-SUnSET) could be used to detect an increase in protein synthesis induced by bilateral synergist ablation (SA) surgery and whether this increase would be similar to that detected using a traditional radioactive technique. To accomplish this mice were subjected to SA or sham surgeries and after 7 days the plantaris muscles were extracted and then incubated in an VX-770 bath for 30 min with.