RESUMO
Loss of physiological regulation of the renal thiazide-sensitive Na+-Cl- cotransporter (NCC) by mutant WNK1 or WNK4 results in pseudohypoaldosteronism type II (PHAII) characterized by arterial hypertension and hyperkalemia. WNK4 normally inhibits NCC, but this effect is lost by eliminating WNK4 catalytic activity or through PHAII-type mutations. In contrast, another member of the WNK family, WNK3, activates NCC. The positive effect of WNK3 on NCC also requires its catalytic activity. Because the opposite effects of WNK3 and WNK4 on NCC were observed in the same expression system, sequences within the WNKs should endow these kinases with their activating or inhibiting properties. To gain insight into the structure-function relationships between the WNKs and NCC, we used a chimera approach between WNK3 and WNK4 to elucidate the domain of the WNKs responsible for the effects on NCC. Chimeras were constructed by swapping the amino or carboxyl terminus domains, which flank the central kinase domain, between WNK3 and WNK4. Our results show that the effect of chimeras toward NCC follows the amino-terminal domain. Thus the amino terminus of the WNKs contains the sequences that are required for their activating or inhibiting properties on NCC.
Assuntos
Hipertensão Renal/fisiopatologia , Túbulos Renais Distais/fisiologia , Proteínas Serina-Treonina Quinases/metabolismo , Pseudo-Hipoaldosteronismo/fisiopatologia , Receptores de Droga/metabolismo , Simportadores de Cloreto de Sódio/metabolismo , Animais , Catálise , Humanos , Hipertensão Renal/metabolismo , Camundongos , Proteínas Mutantes Quiméricas , Oócitos/fisiologia , Proteínas Serina-Treonina Quinases/química , Proteínas Serina-Treonina Quinases/genética , Estrutura Terciária de Proteína , Pseudo-Hipoaldosteronismo/metabolismo , Ratos , Receptores de Droga/genética , Simportadores de Cloreto de Sódio/genética , Relação Estrutura-Atividade , Simportadores/genética , Simportadores/metabolismo , Xenopus laevis , Cotransportadores de K e Cl-RESUMO
The Na(+):K(+):2Cl(-) cotransporter (NKCC2) is the target of loop diuretics and is mutated in Bartter's syndrome, a heterogeneous autosomal recessive disease that impairs salt reabsorption in the kidney's thick ascending limb (TAL). Despite the importance of this cation/chloride cotransporter (CCC), the mechanisms that underlie its regulation are largely unknown. Here, we show that intracellular chloride depletion in Xenopus laevis oocytes, achieved by either coexpression of the K-Cl cotransporter KCC2 or low-chloride hypotonic stress, activates NKCC2 by promoting the phosphorylation of three highly conserved threonines (96, 101, and 111) in the amino terminus. Elimination of these residues renders NKCC2 unresponsive to reductions of [Cl(-)](i). The chloride-sensitive activation of NKCC2 requires the interaction of two serine-threonine kinases, WNK3 (related to WNK1 and WNK4, genes mutated in a Mendelian form of hypertension) and SPAK (a Ste20-type kinase known to interact with and phosphorylate other CCCs). WNK3 is positioned upstream of SPAK and appears to be the chloride-sensitive kinase. Elimination of WNK3's unique SPAK-binding motif prevents its activation of NKCC2, as does the mutation of threonines 96, 101, and 111. A catalytically inactive WNK3 mutant also completely prevents NKCC2 activation by intracellular chloride depletion. Together these data reveal a chloride-sensing mechanism that regulates NKCC2 and provide insight into how increases in the level of intracellular chloride in TAL cells, as seen in certain pathological states, could drastically impair renal salt reabsorption.
Assuntos
Cloretos/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Simportadores de Cloreto de Sódio-Potássio/metabolismo , Motivos de Aminoácidos , Animais , Células Cultivadas , Humanos , Camundongos , Mutação , Oócitos , Fosforilação , Ratos , Simportadores de Cloreto de Sódio-Potássio/química , Simportadores de Cloreto de Sódio-Potássio/genética , Membro 1 da Família 12 de Carreador de Soluto , Treonina/química , Treonina/genética , Treonina/metabolismo , XenopusRESUMO
Microbial flavohaemoglobins are proteins with homology to haemoglobins from higher organisms, but clearly linked to nitric oxide (NO) metabolism by bacteria and yeast. hmp mutant strains of several bacteria are hypersensitive to NO and related compounds and hmp genes are up-regulated by the presence of NO. The regulatory mechanisms involved in hmp induction by NO and the superoxide-generating agent, methyl viologen (paraquat; PQ), are complex, but progressively being resolved. Here we show for the first time that, in Salmonella enterica serovar Typhimurium, hmp transcription is increased on exposure to PQ and demonstrate that RamA, a homologue of MarA is responsible for most of the hmp paraquat regulation. In addition we demonstrate NO-dependent elevation of Salmonella hmp transcription and Hmp accumulation. In both Escherichia coli and Salmonella modest transcriptional repression of hmp is exerted by the iron responsive transcriptional repressor Fur. Finally, in contrast to previous reports, we show that in E. coli and Salmonella, hmp induction by both paraquat and sodium nitroprusside is further elevated in a fur mutant background, indicating that additional regulators are implicated in this control process.