Protein phosphatase 2Cm is a critical regulator of branched-chain amino acid catabolism in mice and cultured cells

Abstract

The branched-chain amino acids (BCAA) are essential amino acids required for protein homeostasis, energy balance, and nutrient signaling. In individuals with deficiencies in BCAA, these amino acids can be preserved through inhibition of the branched-chain-α-ketoacid dehydrogenase (BCKD) complex, the rate-limiting step in their metabolism. BCKD is inhibited by phosphorylation of its E1α subunit at Ser293, which is catalyzed by BCKD kinase. During BCAA excess, phosphorylated Ser293 (pSer293) becomes dephosphorylated through the concerted inhibition of BCKD kinase and the activity of an unknown intramitochondrial phosphatase. Using unbiased, proteomic approaches, we have found that a mitochondrial-targeted phosphatase, PP2Cm, specifically binds the BCKD complex and induces dephosphorylation of Ser293 in the presence of BCKD substrates. Loss of PP2Cm completely abolished substrate-induced E1α dephosphorylation both in vitro and in vivo. PP2Cm-deficient mice exhibited BCAA catabolic defects and a metabolic phenotype similar to the intermittent or intermediate types of human maple syrup urine disease (MSUD), a hereditary disorder caused by defects in BCKD activity. These results indicate that PP2Cm is the endogenous BCKD phosphatase required for nutrient-mediated regulation of BCKD activity and suggest that defects in PP2Cm may be responsible for a subset of human MSUD.

Tissue-specific and Nutrient Regulation of the Branched-chain α-Keto Acid Dehydrogenase Phosphatase, Protein Phosphatase 2Cm (PP2Cm)

“…1, A and B). These results confirmed the original report from our previous study on tissue-specific distribution of the PP2Cm mRNA (25) and demonstrated that the LacZ expression faithfully reflected the endogenous PP2Cm expression pattern. A similar pattern of tissue distribution for PP2Cm was also observed at protein level by immunoblotting (Fig.…”

“…PP2Cm Expression during Development-PP2Cm expression is critical for normal fish development (27) although PP2Cm-deficient mice can develop to term (25). To evaluate the potential role of BCAA catabolic regulation during early development, we examined the LacZ expression at different stages of development in the PP2Cm knock-out mouse.…”

“…Therefore, it is conceivable that pathological stresses down-regulate PP2Cm, leading to impaired BCAA catabolism. However, whether BCAA and BCKA accumulation in turn affect disease progression still remains unknown, although BCKA induces oxidative stress in cells (25). Meanwhile, it remains unclear how PP2Cm gene expression is regulated under pathological conditions.…”

“…PP2Cm has high specificity for phosphor-E1␣. Genetic ablation of the PP2Cm gene in mice leads to hyperphosphorylation of the E1␣ subunit and BCAA catabolic defect associated with a mild form of maple syrup urine disease (25), thus implicating a critical role for PP2Cm as a key regulator of BCAA catabolism. However, the physiological and the molecular bases of PP2Cm function in BCAA catabolic regulation remain poorly understood.…”

Structure-based design and mechanisms of allosteric inhibitors for mitochondrial branched-chain α-ketoacid dehydrogenase kinase

“…Because BDK requires the E2 core for the bulk of kinase activity (11), abrogating BDK binding to LBD from the E2 core will deactivate the kinase. In support of this mechanism, the presence of KIC in HEK293T cells (13,37) or the dietary supplementation of BCAA in type 2 diabetes rat models (38) promotes the dissociation of BDK from the E2 core, resulting in the dephosphorylation of BCKDC.…”