[show abstract][hide abstract] ABSTRACT: To examine the ocular malformations and identify the molecular genetic basis for autosomal recessive ectopia lentis et pupillae in five Norwegian families.
Ten affected persons and 11 first-degree relatives of five Norwegian families underwent ophthalmic and general medical examination. Molecular genetic studies included homozygosity mapping with SNP markers, DNA sequencing, and RT-PCR analysis.
Ocular signs in affected persons were increased median corneal thickness and astigmatism, angle malformation with prominent iris processes, displacement of the pupil and lens, lens coloboma, spherophakia, loss of zonular threads, early cataract development, glaucoma, and retinal detachment. No cardiac or metabolic abnormalities known to be associated with ectopia lentis were detected. Affected persons shared a 0.67 cM region of homozygosity on chromosome 1. DNA sequencing revealed a novel mutation in ADAMTSL4, c.767_786del20. This deletion of 20 base pairs (bp) results in a frameshift and an introduction of a stop codon 113 bp downstream, predicting a C-terminal truncation of the ADAMTSL4 protein (p.Gln256ProfsX38). Expression of truncated ADAMTSL4 mRNA was confirmed by RT-PCR analysis. Three of 190 local blood donors were carriers of this mutation.
Ectopia lentis et pupillae is associated with a number of malformations primarily in the anterior segment of the eye. The causative mutation, which is the first to be described in ectopia lentis et pupillae, disrupts the same gene function previously shown to cause isolated ectopia lentis. The mutation is ancient and may, therefore, be spread to a much larger population than the investigated one.
[show abstract][hide abstract] ABSTRACT: To investigate the diverse clinical manifestations, identify the causative mutation and explain the association with red hair in a family with brittle cornea syndrome (BCS).
Eight family members in three generations underwent ophthalmic, dental, and general medical examinations, including radiologic examination of the spine. Bone mineral density (BMD) and serum levels of vitamin D, parathyroid hormone, and biochemical markers for bone turnover were measured. Skin biopsies were examined by light and transmission electron microscopy. Molecular genetic studies included homozygosity mapping with SNP markers, DNA sequencing, and MC1R genotyping.
At 42 and 48 years of age, respectively, both affected individuals were blind due to retinal detachment and secondary glaucoma. They had extremely thin and bulging corneas, velvety skin, chestnut colored hair, scoliosis, reduced BMD, dental anomalies, hearing loss, and minor cardiac defects. The morphologies of the skin biopsies were normal except that in some areas slightly thinner collagen fibrils were seen in one of the affected individuals. Molecular genetic analysis revealed a novel missense mutation of ZNF469, c.10016G>A, that was predicted to affect the fourth of the five zinc finger domains of ZNF469 by changing the first cysteine to a tyrosine (p.Cys3339Tyr). Both affected individuals were homozygous for the common red hair variant R151C at the MC1R locus.
BCS is a disorder that affects a variety of connective tissues. Reduced BMD and atypical dental crown morphology have not been reported previously. The results confirm that BCS is associated with mutations in ZNF469. The association with red hair in some individuals with BCS is likely to occur by chance.
[show abstract][hide abstract] ABSTRACT: The cAMP-dependent protein kinase (PKA I and II) and the cAMP-stimulated GDP exchange factors (Epac1 and -2) are major cAMP effectors. The cAMP affinity of the PKA holoenzyme has not been determined previously. We found that cAMP bound to PKA I with a K(d) value (2.9 microM) similar to that of Epac1. In contrast, the free regulatory subunit of PKA type I (RI) had K(d) values in the low nanomolar range. The cAMP sites of RI therefore appear engineered to respond to physiological cAMP concentrations only when in the holoenzyme form, whereas Epac can respond in its free form. Epac is phylogenetically younger than PKA, and its functional cAMP site has presumably evolved from site B of PKA. A striking feature is the replacement of a conserved Glu in PKA by Gln (Epac1) or Lys (Epac2). We found that such a switch (E326Q) in site B of human RIalpha led to a 280-fold decreased cAMP affinity. A similar single switch early in Epac evolution could therefore have decreased the high cAMP affinity of the free regulatory subunit sufficiently to allow Epac to respond to physiologically relevant cAMP levels. Molecular dynamics simulations and cAMP analog mapping indicated that the E326Q switch led to flipping of Tyr-373, which normally stacks with the adenine ring of cAMP. Combined molecular dynamics simulation, GRID analysis, and cAMP analog mapping of wild-type and mutated BI and Epac1 revealed additional differences, independent of the Glu/Gln switch, between the binding sites, regarding space (roominess), hydrophobicity/polarity, and side chain flexibility. This helped explain the specificity of current cAMP analogs and, more importantly, lays a foundation for the generation of even more discriminative analogs.
Journal of Biological Chemistry 08/2006; 281(30):21500-11. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: The functional significance of the presence of two major (types I and II) isoforms of the cAMP-dependent protein kinase (PKA) is still enigmatic. The present study showed that peptide substrate enhanced the activation of PKA type I at low, physiologically relevant concentrations of cAMP through competitive displacement of the regulatory RI subunit. The effect was similar whether the substrate was a short peptide or the physiological 60-kDa protein tyrosine hydroxylase. In contrast, substrate failed to affect the cAMP-sensitivity of PKA type II. Size exclusion chromatography confirmed that substrate acted to physically enhance the dissociation of the RIalpha and Calpha subunits of PKA type I, but not the RIIalpha and Calpha subunits of PKA type II. Substrate availability can therefore fine-tune the activation of PKA type I by cAMP, but not PKA type II. The cAMP-dissociated RII and C subunits of PKA type II reassociated much faster than the PKA type I subunits in the presence of substrate peptide. This suggests that only PKA type II is able to rapidly reverse its activation after a burst of cAMP when exposed to high substrate concentration. We propose this as a possible reason why PKA type II is preferentially found in complexes with substrates undergoing rapid phosphorylation cycles.
Journal of Biological Chemistry 05/2005; 280(14):13279-84. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: It is unclear by which receptor cyclic adenosine monophosphate (cAMP) acts to promote neutrophil survival. We found that 8-(4-chlorophenylthio)-2'-O-methyl-cAMP, a specific activator of the recently discovered cAMP receptor, cAMP-regulated guanosine 5'-triphosphate exchange protein directly activated by cAMP, failed to protect human neutrophils from cell death. In contrast, specific activators of cAMP-dependent protein kinase type I (cA-PKI) could protect against death receptor [tumor necrosis factor receptor 1 (TNFR-1), Fas]-mediated apoptosis as well as cycloheximide-accelerated "spontaneous" apoptosis. A novel "caged" cA-PK-activating analog, 8-bromo (8-Br)-acetoxymethyl-cAMP, was more than 20-fold more potent than 8-Br-cAMP to protect neutrophils challenged with TNF-alpha against apoptosis. This analog acted more rapidly than forskolin (which increases the endogenous cAMP production) and allowed us to demonstrate that cA-PK must be activated during the first 10 min after TNF-alpha challenge to protect against apoptosis. The protective effect was mediated solely through cA-PK activation, as it was abolished by the cA-PKI-directed inhibitor Rp-8-Br-cAMPS and the general cA-PK inhibitor H-89. Neutrophils not stimulated by cAMP-elevating agents showed increased apoptosis when exposed to the cA-PK inhibitors Rp-8-Br-cAMPS and H-89, suggesting that even moderate activation of cA-PK is sufficient to enhance neutrophil longevity and thereby contribute to neutrophil accumulation in chronic inflammation.
Journal of Leukocyte Biology 10/2004; 76(3):641-7. · 4.57 Impact Factor
[show abstract][hide abstract] ABSTRACT: The recent discovery of the exchange protein directly activated by cyclic AMP (Epac), an additional and obviously quite common cyclic AMP receptor, leads to a clear demand for suitable tools to discriminate between the well-known protein kinase A (PKA) signalling system, and effects mediated by Epac, in order to allow for independent modulation, and for re-evaluation of systems, formerly potentially misjudged as “PKA-dependent”. As a consequence, experimental setups designed to increase cAMP levels (forskolin, IBMX, etc.) and the use of common cyclic AMP analogs such as 8-bromo-cAMP or 8-CPT-cAMP can no longer considered to be a sufficient prove for phosphorylation via PKA. We present a number of structural analogs of cyclic nucleotides, that respect the even more complex system of cyclic AMP signalling after the discovery of Epac, and give a help for picking out suitable tools for selective modulation of cAMP and cGMP signalling systems.
12th International Conference on Second Messengers and Phosphoproteins; 08/2004
[show abstract][hide abstract] ABSTRACT: Little is known about the relative role of cAMP-dependent protein kinase (cAPK) and guanine exchange factor directly activated by cAMP (Epac) as mediators of cAMP action. We tested cAMP analogs for ability to selectively activate Epac1 or cAPK and discriminate between the binding sites of Epac and of cAPKI and cAPKII. We found that commonly used cAMP analogs, like 8-Br-cAMP and 8-pCPT-cAMP, activate Epac and cAPK equally as well as cAMP, i.e. were full agonists. In contrast, 6-modified cAMP analogs, like N6-benzoyl-cAMP, were inefficient Epac activators and full cAPK activators. Analogs modified in the 2'-position of the ribose induced stronger Epac1 activation than cAMP but were only partial agonists for cAPK. 2'-O-Alkyl substitution of cAMP improved Epac/cAPK binding selectivity 10-100-fold. Phenylthio substituents in position 8, particularly with MeO- or Cl- in p-position, enhanced the Epac/cAPK selectivity even more. The combination of 8-pCPT- and 2'-O-methyl substitutions improved the Epac/cAPK binding selectivity about three orders of magnitude. The cAPK selectivity of 6-substituted cAMP analogs, the preferential inhibition of cAPK by moderate concentrations of Rp-cAMPS analogs, and the Epac selectivity of 8-pCPT-2'-O-methyl-cAMP was also demonstrated in intact cells. Using these compounds to selectively modulate Epac and cAPK in PC-12 cells, we observed that analogs selectively activating Epac synergized strongly with cAPK specific analogs to induce neurite outgrowth. We therefore conclude that cAMP-induced neurite outgrowth is mediated by both Epac and cAPK.
Journal of Biological Chemistry 10/2003; 278(37):35394-402. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: cAMP is involved in a wide variety of cellular processes that were thought to be mediated by protein kinase A (PKA). However, cAMP also directly regulates Epac1 and Epac2, guanine nucleotide-exchange factors (GEFs) for the small GTPases Rap1 and Rap2 (refs 2,3). Unfortunately, there is an absence of tools to discriminate between PKA- and Epac-mediated effects. Therefore, through rational drug design we have developed a novel cAMP analogue, 8-(4-chloro-phenylthio)-2'-O-methyladenosine-3',5'-cyclic monophosphate (8CPT-2Me-cAMP), which activates Epac, but not PKA, both in vitro and in vivo. Using this analogue, we tested the widespread model that Rap1 mediates cAMP-induced regulation of the extracellular signal-regulated kinase (ERK). However, both in cell lines in which cAMP inhibits growth-factor-induced ERK activation and in which cAMP activates ERK, 8CPT-2Me-cAMP did not affect ERK activity. Moreover, in cell lines in which cAMP activates ERK, inhibition of PKA and Ras, but not Rap1, abolished cAMP-mediated ERK activation. We conclude that cAMP-induced regulation of ERK and activation of Rap1 are independent processes.
[show abstract][hide abstract] ABSTRACT: The present invention relates to novel compounds for modulating the activity of exchange proteins directly activated by cAMP (Epacs). In particular, the present invention relates to cAMP analogues that specifically modulate the activity of Epacs. Examples of the compounds of the invention are substituted deoxyadenosine-cyclic monosphosphates. The invention further relates to pharmaceutical compositions comprising the novel compounds, and the use of the compounds in the treatment of diseases like cancer, chronic inflammation, thrombosis and/or type-2 diabetes mellitus in humans and/or animals.
[show abstract][hide abstract] ABSTRACT: The present invention relates to novel compounds for modulating the activity
of exchange proteins directly activated by cAMP (Epacs). In particular, the
present invention relates to cAMP analogues that specifically modulate the
activity of Epacs. The invention further relates to pharmaceutical
compositions comprising the novel compounds, and the use of the compounds in
the treatment of humans and/or animals.
Ref. No: Canadian Patent CA 2488611, Year: 06/2002
[show abstract][hide abstract] ABSTRACT: The complex of the subunits (RIalpha, Calpha) of cAMP-dependent protein kinase I (cA-PKI) was much more stable (K(d) = 0.25 microm) in the presence of excess cAMP than previously thought. The ternary complex of C subunit with cAMP-saturated RIalpha or RIIalpha was devoid of catalytic activity against either peptide or physiological protein substrates. The ternary complex was destabilized by protein kinase substrate. Extrapolation from the in vitro data suggested about one-fourth of the C subunit to be in ternary complex in maximally cAMP-stimulated cells. Cells overexpressing either RIalpha or RIIalpha showed decreased CRE-dependent gene induction in response to maximal cAMP stimulation. This could be explained by enhanced ternary complex formation. Modulation of ternary complex formation by the level of R subunit may represent a novel way of regulating the cAMP kinase activity in maximally cAMP-stimulated cells.
Journal of Biological Chemistry 05/2002; 277(16):13443-8. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: cAMP analogues, systematically substituted at position 8 of the adenine moiety (C8), were tested quantitatively for binding to each cAMP interaction site (A and B) of the regulatory subunits of cAMP-dependent protein kinase type I (RI) and II (RII). Site AII did not accommodate cAMP analogues with any bulk at position 8, whereas site AI accepted even bulky 8-substituents. This implies that the narrow, buried pocket of site AI facing position C8 of cAMP in the RI-cAMP crystal [Su, Y., Dostmann, W. R., Herberg, F. W., Durick, K., Xuong, N. H., Ten Eyck, L., Taylor, S. S., and Varughese, K. I. (1995) Science 269, 807-813] must undergo considerable conformational change and still support high-affinity cAMP analogue binding. The B sites of RI and RII differed in three respects. First, site BI had a lower affinity than site BII for cAMP analogues with hydrophobic, bulky 8-substituents. Second, site BI had a preference for substituents with hydrogen bonding donor potential close to C8, whereas site BII had a preference for substituents with hydrogen bonding acceptor potential. This implies that Tyr(371) of RI and the homologous Tyr(379) of RII differ in their hydrogen bonding preference. Third, site BI preferred analogues with a positively charged amino group that was an extended distance from C8, whereas site BII discriminated against a positive charge. The combined results allow refinement of the cAMP binding site geometry of RI and RII in solution, and suggest design of improved isozyme-specific cAMP analogues.