BackgroundPersistent pulmonary hypertension of the newborn (PPHN) is characterized by elevated pulmonary vascular resistance. Endogenous nitric oxide is critical for regulation of pulmonary vascular r Show more
BackgroundPersistent pulmonary hypertension of the newborn (PPHN) is characterized by elevated pulmonary vascular resistance. Endogenous nitric oxide is critical for regulation of pulmonary vascular resistance. Nitric oxide is generated from L-arginine, supplied by the urea cycle (UC). We hypothesized that polymorphisms in UC enzyme genes and low concentrations of UC intermediates are associated with PPHN.MethodsWe performed a family-based candidate gene analysis to study 48 single-nucleotide polymorphisms (SNPs) in six UC enzyme genes. Genotyping was carried out in 94 infants with PPHN and their parents. We also performed a case-control analysis of 32 cases with PPHN and 64 controls to identify an association between amino-acid levels on initial newborn screening and PPHN.ResultsThree SNPs (rs41272673, rs4399666, and rs2287599) in carbamoyl phosphate synthase 1 gene (CPS1) showed a significant association with PPHN (P=0.02). Tyrosine levels were significantly lower (P=0.003) and phenylalanine levels were significantly higher (P=0.01) in cases with PPHN. There was no difference in the arginine or citrulline levels between the two groups.ConclusionsThis study suggests an association (P<0.05) between SNPs in CPS1 and PPHN. These findings warrant further replication in larger cohorts of patients. Show less
START-dependent transcription in Saccharomyces cerevisiae is regulated by two transcription factors SBF and MBF, whose activity is controlled by the binding of the repressor Whi5. Phosphorylation and Show more
START-dependent transcription in Saccharomyces cerevisiae is regulated by two transcription factors SBF and MBF, whose activity is controlled by the binding of the repressor Whi5. Phosphorylation and removal of Whi5 by the cyclin-dependent kinase (CDK) Cln3-Cdc28 alleviates the Whi5-dependent repression on SBF and MBF, initiating entry into a new cell cycle. This Whi5-SBF/MBF transcriptional circuit is analogous to the regulatory pathway in mammalian cells that features the E2F family of G1 transcription factors and the retinoblastoma tumor suppressor protein (Rb). Here we describe genetic and biochemical evidence for the involvement of another CDK, Pcl-Pho85, in regulating G1 transcription, via phosphorylation and inhibition of Whi5. We show that a strain deleted for both PHO85 and CLN3 has a slow growth phenotype, a G1 delay, and is severely compromised for SBF-dependent reporter gene expression, yet all of these defects are alleviated by deletion of WHI5. Our biochemical and genetic tests suggest Whi5 mediates repression in part through interaction with two histone deacetylases (HDACs), Hos3 and Rpd3. In a manner analogous to cyclin D/CDK4/6, which phosphorylates Rb in mammalian cells disrupting its association with HDACs, phosphorylation by the early G1 CDKs Cln3-Cdc28 and Pcl9-Pho85 inhibits association of Whi5 with the HDACs. Contributions from multiple CDKs may provide the precision and accuracy necessary to activate G1 transcription when both internal and external cues are optimal. Show less