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Jonathan A Cohn

Publications and source records attributed to Jonathan A Cohn.

7 recordsLinked to original sources
PubMed2004

Protein kinase A regulates ATP hydrolysis and dimerization by a CFTR (cystic fibrosis transmembrane conductance regulator) domain.

Gating of the CFTR Cl- channel is associated with ATP hydrolysis at the nucleotide-binding domains (NBD1, NBD2) and requires PKA (protein kinase A) phosphorylation of the R domain. The manner in which the NBD1, NBD2 and R domains of CFTR (cystic fibrosis transmembrane conductance regulator) interact to achieve a properly regulated ion channel is largely unknown. In this study we used bacterially expressed recombinant proteins to examine interactions between these soluble domains of CFTR in vitro. PKA phosphorylated a fusion protein containing NBD1 and R (NBD1-R-GST) on CFTR residues Ser-660, Ser-700, Ser-712, Ser-737, Ser-768, Ser-795 and Ser-813. Phosphorylation of these serine residues regulated ATP hydrolysis by NBD1-R-GST by increasing the apparent K(m) for ATP (from 70 to 250 microM) and the Hill coefficient (from 1 to 1.7) without changing the V(max). When fusion proteins were photolabelled with 8-azido-[alpha-32P]ATP, PKA phosphorylation increased the apparent k(d) for nucleotide binding and it caused binding to become co-operative. PKA phosphorylation also resulted in dimerization of NBD1-R-GST but not of R-GST, a related fusion protein lacking the NBD1 domain. Finally, an MBP (maltose-binding protein) fusion protein containing the NBD2 domain (NBD2-MBP) associated with and regulated the ATPase activity of PKA-phosphorylated NBD1-R-GST. Thus when the R domain in NBD1-R-GST is phosphorylated by PKA, ATP binding and hydrolysis becomes co-operative and NBD dimerization occurs. These findings suggest that during the activation of native CFTR, phosphorylation of the R domain by PKA can control the ability of the NBD1 domain to hydrolyse ATP and to interact with other NBD domains.

Adenosine Triphosphate↗
PubMed2003

Motion--genetic testing is useful in the diagnosis of nonhereditary pancreatic conditions: arguments against the motion.

Mutations of two genes, the cystic fibrosis transmembrane conductance regulator gene (CFTR) and the pancreatic secretory trypsin inhibitor gene (PSTI), are associated with an increase in the risk of idiopathic chronic pancreatitis. Persons who have mutations of both CFTR alleles (one severely and one mildly affected) are especially susceptible to this disease. Because these compound heterozygotes have sufficient residual CFTR function, they do not develop cystic fibrosis lung disease. One PSTI mutation, N34S, independently increases the risk of pancreatitis. Thus, the risk of pancreatitis is greatest among individuals who are CFTR compound heterozygotes and who also have the PSTI mutation. Nonetheless, most people with CFTR and PSTI mutations do not develop pancreatitis. This fact indicates that environmental influences and gene-gene interactions also affect pancreatitis risk. Although CFTR and PSTI genetic testing can identify persons at an increased risk of pancreatitis, there are several reasons why the routine screening of individuals with nonhereditary pancreatitis is not recommended at this time: most disease-associated mutations are not detected by readily available techniques, genetic counselling guidelines do not exist, most patients with mutations do not develop pancreatitis and the results of testing do not affect the clinical management of pancreatitis.

Chronic Disease↗
PubMed2003

5' exon replacement and repair by spliceosome-mediated RNA trans-splicing.

Spliceosome-mediated RNA trans-splicing (SMaRT) has been used previously to reprogram mutant endogenous CFTR and factor VIII mRNAs in human epithelial cell and tissue models and knockout mice, respectively. Those studies used 3' exon replacement (3'ER); a process in which the distal portion of RNA is reprogrammed. Here, we also show that the 5' end of mRNA can be completely rewritten by 5'ER. For proof-of-concept, and to test whether 5'ER could generate functional CFTR, we generated a mutant minigene target containing CFTR exons 10-24 (deltaF508) and a mini-intron 10, and a pretrans-splicing molecule (targeted to intron 10) containing CFTR exons 1-10 (+F508), and tested these two constructs in 293T cells for anion efflux transport. Cells cotransfected with target and PTM showed a consistent increase in anion efflux, but there was no response in control cells that received PTM or target alone. Using a LacZ reporter system to accurately quantify trans-splicing efficiency, we tested several unique PTM designs. These studies provided two important findings as follows: (1) efficient trans-splicing can be achieved by binding the PTM to different locations in the target, and (2) relatively few changes in PTM design can have a profound impact on trans-splicing activity. Tethering the PTM close to the target 3' splice site (as opposed to the donor site) and inserting an intron in the PTM coding resulted in a 65-fold enhancement of LacZ activity. These studies demonstrate that (1) SMaRT can be used to reprogram the 5' end of mRNA, and (2) efficiency can be improved substantially.

Cell Line↗
PubMed2002

Partial correction of endogenous DeltaF508 CFTR in human cystic fibrosis airway epithelia by spliceosome-mediated RNA trans-splicing.

Spliceosome-mediated RNA trans-splicing (SMaRT) was investigated as a means for functionally correcting endogenous DeltaF508 cystic fibrosis transmembrane conductance regulator (CFTR) transcripts using in vitro human cystic fibrosis (CF) polarized airway epithelia and in vivo human CF bronchial xenografts. Recombinant adenovirus (Ad.CFTR-PTM) encoding a pre-therapeutic molecule (PTM) targeted to CFTR intron 9 corrected transepithelial cyclic AMP (cAMP)-sensitive short-circuit current (Isc) in DeltaF508 homozygous epithelia to a level 16% of that observed in normal human bronchial epithelia. Molecular analyses using RT-PCR and western blotting confirmed SMaRT-mediated partial correction of endogenous DeltaF508 messenger RNA (mRNA) transcripts and protein. In an in vivo model of DeltaF508 CF airway epithelia, human CF bronchial xenografts infected with Ad.CFTR-PTM also demonstrated partial correction of CFTR-mediated Cl- permeability at a level 22% of that seen in non-CF xenografts. These results provide functional evidence for SMaRT-mediated repair of mutant endogenous CFTR mRNA in intact polarized CF airway epithelial models.

Adenoviridae↗
PubMed2002

Idiopathic pancreatitis related to CFTR: complex inheritance and identification of a modifier gene.

Idiopathic chronic pancreatitis (ICP) is the leading cause of nonalcoholic chronic pancreatitis. This study examined a series of patients with ICP to determine the prevalence and role of mutations of the cystic fibrosis gene (CFTR) and of a trypsin inhibitor gene (PSTI). Genetic testing was done in 39 patients with ICP. In this series, 17 patients had CFTR mutations and 9 had PSTI mutations. Pancreatitis risk was increased 14-fold by having the N34S PST1 mutation, 40-fold by having two abnormal copies of CFTR, and 600-fold by having both. In patients with two CFTR mutations, extrapancreatic clinical findings and nasal bioelectric responses suggested reduced residual CFTR protein function. Thus, pancreatitis risk showed complex inheritance and was highest in individuals who have abnormalities in both the pancreatic ducts (CFTR) and acini (PSTI). These findings indicate that PSTI is a modifier gene for CFTR-related ICP and have implications for the classification, diagnosis, and pathogenesis of pancreatitis.

Adolescent↗