MCCC1 and cancer: Although post-translational modifications of 3-methylcrotonyl-CoA carboxylase, mainly the MCCC1 subunit, were found to be a key factor for the complex formation between MCCC1 and MCCC2 and for the catalytic activity in leucine metabolism and insulin secretion, which were regulated by SIRT4 7, it remains to be determined whether the dynamic regulation of post-translational modifications of MCCC in response to oncogenic signaling cues plays any roles in cancer.