A corticosteroid-induced gene expressing an "IsK-like" K+ channel activity in Xenopus oocytes.

Abstract

Screening a rat colon cDNA library for aldosterone-induced genes resulted in the molecular cloning of a cDNA whose corresponding mRNA is strongly induced in the colon by dexamethasone, aldosterone, and a low NaCl diet. A similar mRNA was detected in kidney papilla but not in brain, heart, or skeletal muscle. Xenopus laevis oocytes injected with cRNA synthesized from this clone, designated CHIF (channelinducing factor), express a K+-specific channel activity. The biophysical, pharmacological, and regulatory characteristics of this channel are very similar to those reported before for IsK (minK). These include: slow (T > 20 s) activation by membrane depolarization with a threshold potential above -50 mV, blockade by clofilium, inhibition by phorbol ester, and activation by 8-bromoadenosine 3',5'-cyclic monophosphate and high cytoplasmic Ca2+. The primary structure of this clone, however, shows no homology to IsK. Instead, CHIF exhibits >50%o similarity to two other short bitopic membrane proteins, phospholemman and the y subunit of Na+,K+-ATPase. The data are consistent with the possibility that CHIF is a member of a family of transmembrane regulators capable of activating endogenous oocyte transport proteins.

Hydration-optimized oriented phospholipid bilayer samples for solid-state NMR structural studies of membrane proteins

“…This was tested by preparing a sample of the uniformly 15 N-labeled membrane protein CHIF (channel inducing factor) in oriented lipid bilayers, and recording its 15 N chemical shift spectrum both before and after hydration-optimization. CHIF is a 67 amino acid, single-pass membrane protein, that is upregulated by aldosterone and corticosteroids in mammalian kidney and intestinal tracks, where it associates with the Na, K-ATPase to regulate Na + and K + homeostasis [21,22]. It is a member of the FXYD family proteins that are emerging as auxiliary, tissue-specific and physiological state-specific, subunits of the Na, K-ATPase [23].…”

NMR of membrane proteins in micelles and bilayers: The FXYD family proteins

“…FXYD1 (PLM; phospholemman) is the principal substrate of hormone-stimulated phosphorylation by cAMP-dependent protein kinase A and C in heart sarcolemma [20]. FXYD2 (gamma) and FXYD4 (CHIF; channel-inducing factor; corticosteroid hormone induced factor), are each expressed in distinct, specialized segments of the kidney, with unique expression patterns that help explain the physiological differences in Na,K-ATPase activity among the nephron segments [21][22][23][24][25]. FXYD3 (Mat8; mammary tumor protein 8 kDa) is expressed in cancers and plays a role in tumor progression [26,27].…”

Regulation of Na,K-ATPase by PLMS, the Phospholemman-like Protein from Shark

“…Cloning and Sequencing-First strand cDNA synthesis was carried out in a total reaction volume of 20 l containing 5 g of total rectal gland RNA, 75 mM Tris-HCl, pH 8.3, 3 mM MgCl 2 , 10 mM DTT, 10 M oligo(dT) [12][13][14][15][16][17][18] , 1 mM each of deoxyribonucleotide triphosphates (dNTPs; dATP, dGTP, dCTP, and dTTP), and 200 units of Superscript II (Invitrogen, Paisley, UK). The reaction was incubated at 45°C for 2 h and then stored frozen at Ϫ20°C for use in PCR.…”

“…This family includes phospholemman (PLM or FXYD1) (14), the ␥-subunit (FXYD2) (15), mammary tumor protein of 8-kDa molecular mass (MAT-8 or FXYD3) (16), channel-inducing factor (CHIF or FXYD4) (17), related to ion channel (RIC or FYXD5) (18), as well as FXYD6 and FXYD7.…”