Previous reports showed that FBXW7 is involved in the ubiquitination and degradation of mTOR in cancer cells (Mao et al, 2008), while in the current study, we examined major components of the mTOR signaling via mass spectrum and found that FBXW7 specifically targeted S6K1 in BAT, suggesting FBXW7 targets feature tissue selectivity for ubiquitination. This evidence concerns the gene RPS6KB1 and cancer.