Brca1 Is Expressed And Binds To Phosphorylated Acetyl Coa Carboxylase In Skeletal Muscle

Abstract

Breast cancer early onset type 1 (BRCA1) is an estrogen sensitive gene known to play a critical role in the prevention breast tumorigenesis and is also thought to contribute to DNA damage repair. Recently in breast tissue, BRCA1 was identified as a binding partner and regulator of acetyl CoA carboxylase (ACC) activity suggesting BRCA1 may act as a regulator of lipid metabolism. Currently, the role of BRCA1 has yet to be characterized in skeletal muscle. The purpose of this study was to determine if BRCA1 was expressed in skeletal muscle and if it could be immunoprecipated with the phosphorylated form of ACC (ACC-p). BRCA1 mRNA and protein was identified in skeletal muscle with the highest levels being detected in more oxidative muscles (i.e. soleus and gastrocnemius) and lower levels detected in glycolytic muscles (i.e. tibialis anterior). Further, our data suggest that BRCA1 expression in skeletal muscle is estrogen sensitive, in that BRCA1 mRNA expression was higher in female mice compared to both male and surgically ovariectomized female mice. To determine if BRCA1 could be immunoprecipated with ACC-p, acute treadmill running was utilized to induce increases in ACC-p content through exercise-induced activation of AMP-kinase. In preliminary experiments we found that female mice running at treadmill speeds of ∼27m/min for 25-30 min elicited significant increases in AMPK phosphorylation (Thr-172) and ACC-p (Ser79) content. Female C57/BL6 mice were acclimated to treadmill exercise and were then subjected to an acute bout of exercise (26.5±0.3 m/min for 28.3±2.2min). Immediately after the exercise bout, the gastrocnemius muscle was removed and snap frozen in liquid nitrogen. In response to an acute bout of treadmill exercise ACC phosphorylation (Ser 79) was increased significantly by 43% compared to the sedentary mice. No changes in total ACC were detected between groups. After samples underwent immunoprecipation with an antibody specific to BRCA1, we detected significantly more ACC-p bound to BRCA1 (176%) in the exercised group compared to the sendentary group. There were no differences detected in the total amount of BRCA1 immunoprecipitated between groups. These data indicate that in similar fashion to breast tissue, BRCA1 can bind to the phosphorylated form of ACC in skeletal muscle. These results suggest that BRCA1 is expressed in skeletal muscle and is potentially acting as a novel regulator of ACC in skeletal muscle in response to an acute bout of exercise.