Phenylalanine hydroxylase variants interact with the co‐chaperone DNAJC12

Abstract

DNAJC12, a type III member of the HSP40/DNAJ family, has been identified as the specific co‐chaperone of phenylalanine hydroxylase (PAH) and the other aromatic amino acid hydroxylases. DNAJ proteins work together with molecular chaperones of the HSP70 family to assist in proper folding and maintenance of intracellular stability of their clients. Autosomal recessive mutations in DNAJC12 were found to reduce PAH levels, leading to hyperphenylalaninemia (HPA) in patients without mutations in PAH. In this work, we investigated the interaction of normal wild‐type DNAJC12 with mutant PAH in cells expressing several PAH variants associated with HPA in humans, as well as in the Enu1/1 mouse model, homozygous for the V106A‐Pah variant, which leads to severe protein instability, accelerated PAH degradation and mild HPA. We found that mutant PAH exhibits increased ubiquitination, instability, and aggregation compared with normal PAH. In mouse liver lysates, we showed that DNAJC12 interacts with monoubiquitin‐tagged PAH. This form represented a major fraction of PAH in the Enu1/1 but was also present in liver of wild‐type PAH mice. Our results support a role of DNAJC12 in the processing of misfolded ubiquitinated PAH by the ubiquitin‐dependent proteasome/autophagy systems and add to the evidence that the DNAJ proteins are important players both for proper folding and degradation of their clients.

Pathogenic variants of DNAJC12 and evaluation of the encoded cochaperone as a genetic modifier of hyperphenylalaninemia

“…Further assays are needed to confirm this hypothesis. This highlights the major role of DNAJC12 in targeting misfolded PAH for degradation (Jung‐Kc et al, 2019). These results open up the possible use of pharmacological treatments designed to upregulate levels of molecular chaperones or cochaperones.…”

Screening of key genes associated with R‑CHOP immunochemotherapy and construction of a prognostic risk model in diffuse large B‑cell lymphoma

“…Carboxylesterases are found to hydrolyze two anticancer agents, capecitabine and irinotecan (60). DnaJ heat shock protein family member C12 ( DNAJC12 ) encodes a member of a subclass of the heat shock protein 40 kDa family that is involved in a number of important biological functions (61,62). High expression of DNAJC12 functions as a negative predictive factor for the response to neoadjuvant concurrent chemotherapy in rectal cancer (63).…”

Protein Degradation and the Pathologic Basis of Phenylketonuria and Hereditary Tyrosinemia

“…DNAJC12 is involved in PAH folding and interacts with the monoubiquitinated PAH variant, marking it for the Ub-dependent proteasomal/autophagy degradation system. Further studies are ongoing to elucidate the role of DNAJC12 in regulating PAH and PAH mutants [ 25 , 101 ]. Gene therapy and the ectopic expression of wild type chaperones might help to restore the partially functional mutant proteins [ 102 , 103 ].…”

“…The allosterically activated form of PAH is majorly responsible for the conversion of phenylalanine to tyrosine; however, stability calculations are not possible for this form as its high resolution structure is not yet available. Nonetheless, certain experimental reports suggested increased aggregation, high instability, and accelerated degradation of the PAH mutant expressed in Enu 1/1 and Enu 1/2 heteroallelic mouse model, primary hepatocytes and COS-7 cells [ 24 , 25 , 26 ]. The mutant PAH proteins (e.g., p.V106A) expressed in Enu 1/1 mouse model, are also known to be highly ubiquitinated in vitro and in vivo, targeting it for proteasome-mediated degradation and selective autophagy [ 24 ].…”