ABSTRACT
The leucine zipper-like transcriptional regulator 1 (LZTR1) protein, an adaptor for cullin 3 (CUL3) ubiquitin ligase complex, is implicated in human disease, yet its mechanism of action remains unknown. We found that Lztr1 haploinsufficiency in mice recapitulates Noonan syndrome phenotypes, whereas LZTR1 loss in Schwann cells drives dedifferentiation and proliferation. By trapping LZTR1 complexes from intact mammalian cells, we identified the guanosine triphosphatase RAS as a substrate for the LZTR1-CUL3 complex. Ubiquitome analysis showed that loss of Lztr1 abrogated Ras ubiquitination at lysine-170. LZTR1-mediated ubiquitination inhibited RAS signaling by attenuating its association with the membrane. Disease-associated LZTR1 mutations disrupted either LZTR1-CUL3 complex formation or its interaction with RAS proteins. RAS regulation by LZTR1-mediated ubiquitination provides an explanation for the role of LZTR1 in human disease.
Subject(s)
Noonan Syndrome/genetics , Transcription Factors/genetics , Ubiquitination/genetics , ras Proteins/metabolism , Animals , Cell Dedifferentiation , Cell Proliferation , Cullin Proteins/metabolism , Disease Models, Animal , Female , HEK293 Cells , Haploinsufficiency , HeLa Cells , Humans , Male , Mice, Mutant Strains , Mutation , Schwann Cells/cytology , Schwann Cells/metabolismABSTRACT
Acute cellular rejection (ACR) is the adverse response of the recipient's immune system against the allogeneic graft. Using human surveillance endomyocardial biopsies (EMBs) manifesting ACR and murine allogeneic grafts, we profiled implicated microRNAs (miRs) and mRNAs. MiR profiling showed that miR-21, -142-3p, -142-5p, -146a, -146b, -155, -222, -223, and -494 increased during ACR in humans and mice, whereas miR-149-5p decreased. mRNA profiling revealed 70 common differentially regulated transcripts, all involved in immune signaling and immune-related diseases. Interestingly, 33 of 70 transcripts function downstream of IL-6 and its transcription factor spleen focus forming virus proviral integration oncogene (SPI1), an established target of miR-155, the most upregulated miR in human EMBs manifesting rejection. In a mouse model of cardiac transplantation, miR-155 absence and pharmacological inhibition attenuated ACR, demonstrating the causal involvement and therapeutic potential of miRs. Finally, we corroborated our miR signature in acute cellular renal allograft rejection, suggesting a nonorgan specific signature of acute rejection. We concluded that miR and mRNA profiling in human and murine ACR revealed the shared significant dysregulation of immune genes. Inflammatory miRs, for example miR-155, and transcripts, in particular those related to the IL-6 pathway, are promising therapeutic targets to prevent acute allograft rejection.
