Multifunctional calcium/calmodulin-dependent protein kinase (CaM kinase) is an enzyme mediating calcium-dependent signal transduction pathways. CaM kinase exists in a variety of isoforms, each with a distinct tissue-specific expression pattern, that enables the kinase to regulate multiple functions in mammalian systems. Here we report the chromosomal localization of the previously cloned human gamma-CaM kinase gene (CAMKG). By using a mapping panel of human x Chinese hamster somatic cell hybrid lines and fluorescence in situ hybridization, we have assigned human CAMKG to chromosome 10q22. We have partially cloned the murine gamma-CaM kinase gene and mapped it Camkg to mouse chromosome 14 by analyzing a panel of mouse x rodent somatic cell hybrid lines. A recessive gene, asa, implicated in the control of autoimmune response, is located within the predicted region for Camkg.
Multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase) is a mediator of calcium signals in diverse signaling pathways. In human lymphocytes and epithelial tissues, CaM kinase activates a chloride channel via a Ca(2+)-dependent pathway which is preserved in cystic fibrosis. To characterize the CaM kinase present in these tissues we have cloned an isoform of this kinase from human T lymphocytes. We show the cDNA structure of two variants of this human CaM kinase, gamma B and gamma C, which are predicted to translate to 518 and 495 amino acids, respectively. Amino acid differences between these isoforms and the rat brain gamma isoform (which we refer to as gamma A) are localized to the variable domain. We used RNase protection of this variable region to reveal the level of expression of gamma B and gamma C CaM kinase mRNAs in nine human tissues and cell lines. When transfected into Jurkat T cells, the gamma B cDNA encoded a functional kinase which cosedimented on sucrose gradients with endogenous T cell CaM kinase activity and formed a large multimeric enzyme. The recombinant gamma B isoform displayed two phases of autophosphorylation characteristic of CaM kinases, including the phase which converts it to a partially Ca(2+)-independent species. Site-directed mutagenesis of the predicted autoinhibitory domain yielded a mutant which was approximately 37% active in the absence of Ca2+/calmodulin, confirming the region as critical for autoregulation, and suggesting this mutant as a tool for studying the role of CaM kinase in nonneuronal tissues.
Phosphorylation of the cystic fibrosis transmembrane conductance regulator (CFTR) by cAMP-dependent protein kinase leads to chloride flux in epithelial cells. Is CFTR also required for the calcium-dependent activation of chloride channels? We used antisense oligodeoxynucleotides to CFTR to reduce the expression of CFTR in colonic and tracheal epithelial cells. The antisense oligomers were a pair of adjacent 18-mers complementary to nucleotides 1-18 and 19-36 of CFTR mRNA. Sense and misantisense oligomers served as controls. A 48-h antisense treatment reduced the expression of CFTR protein as assayed by immunoprecipitation and autoradiography to 26% of the level in sense-treated T84 cells. Whole-cell patch clamp revealed that a 48-h antisense treatment of T84 and 56FHTE-8o- fetal tracheal epithelial cells reduced the cAMP-activated chloride current to approximately 10% of that in sense-treated cells. The half-life of functional CFTR is less than 24 h in these cells. In contrast, the calcium-activated chloride current was not affected by antisense treatment. Hence, the cAMP and calcium pathways are separate. CFTR is required for the cAMP pathway but not for the calcium pathway.
Cystic fibrosis (CF) is the most common lethal genetic disease among Caucasians, primarily affecting epithelial tissues of the lung and gut. Mutations in a single gene, the cystic fibrosis transmembrane conductance regulator (CFTR), are responsible for this disease. Whether a physiological defect exists in the immune system of CF patients has remained controversial. A chloride ion transport defect has been described in human CF-derived lymphocytes; however, it has not been possible to detect CFTR mRNA in lymphocytes. We report here that normal human B-lymphoblasts display whole cell Cl- conductances induced by calcium-mediated pathways, volume regulation, and cAMP which are equivalent to currents described in epithelial cells. B-lymphoblasts from CF-affected humans demonstrated defective Cl- conductance regulation by cAMP but preserved regulation by calcium-mediated and volume regulation mechanisms. CFTR involvement in cAMP regulation of Cl- conductance in lymphocytes is further supported by our demonstration of the presence of appropriately spliced CFTR mRNA segments in human B and T lymphocytes as detected by an optimized reverse-transcription and polymerase chain reaction approach. The identity of the amplified products was confirmed by hybridization to CFTR-specific probes and DNA sequencing. Furthermore, the 3′-end of the gene was found in a T cell cDNA library. We conclude that CFTR mRNA is expressed in lymphocytes, consistent with the cAMP regulation of chloride transport present in normal lymphocytes but defective in CF-derived lymphocytes.
Patch-clamp studies have identified a cAMP-dependent Cl- conductance in lymphocytes that is defectively regulated in cystic fibrosis. In this study we used 125I efflux and whole-cell patch-clamp studies to investigate whether prostaglandin E1 (PGE1), an agonist that generates intracellular cAMP in Jurkat T lymphocytes, activates a Cl- conductance. Stimulation of T cells by externally applied PGE1 stimulated 125I efflux and activated a slowly developing membrane current. When external and internal Cl- were about equal, the current reversed at about zero mV, but when external Cl- was lowered from 157 to 7 mM the reversal potential shifted 75 mV in the positive direction, demonstrating that the current carrier was Cl-. In addition, the current was blocked by 10 microM 5-nitro-2(3-phenylpropylamino) benzoic acid (NPPB), a potent Cl- channel blocker. A membrane-permeable cAMP analog mimicked the effect of PGE1, whereas intracellular application of a cAMP antagonist Rp-cAMP blocked the effect of PGE1. Addition of purified catalytic subunit of cAMP-dependent protein kinase (PKA) plus ATP to the recording pipette also activated a similar current, whereas internally applied Walsh inhibitor, the synthetic peptide inhibitor of PKA, blocked the PGE1 effect. These results suggest that PGE1, acting through PKA, activates a Cl- current in Jurkat T cells.