Accumulation of β_m, a structural member of X,K-ATPase β-subunit family, in nuclear envelopes of perinatal myocytes

Abstract

Zhao, Hao, Nikolay B. Pestov, Tatyana V. Korneenko, Mikhail I. Shakhparonov, and Nikolai N. Modyanov. Accumulation of ␤ m, a structural member of X,K-ATPase ␤-subunit family, in nuclear envelopes of perinatal myocytes. Am J Physiol Cell Physiol 286: C757-C767, 2004. First published December 3, 2003 10.1152/ ajpcell.00358.2003.-Recently discovered muscle-specific ␤ m protein is structurally closely related to the X,K-ATPase ␤-subunits. However, it has a number of unique properties such as predominant localization in intracellular stores and lack of association with known X,K-ATPase ␣-subunits on heterologous coexpression. In this study, the primary structure of mouse ␤ m was determined and developmental regulation of the gene (ATP1B4) was analyzed. The expression is first detected at day 14 of gestation, is sharply increased at day 16, and reaches its maximum at day 18. After birth, the expression quickly decreases and is hardly detectable in adult mice. A more detailed subcellular localization study was undertaken, and its results indicate that ␤ m not only is located in sarcoplasmic reticulum but is concentrated in nuclear envelopes of both prenatal and postnatal skeletal muscles. Immunohistochemical studies show that ␤ m is specific to myocytes and, at the subcellular level, many nuclear envelopes are intensively labeled in both fetal and newborn skeletal muscles. Accordingly, ␤ m is detected by immunoblotting in purified nuclei and nuclear membranes from neonatal skeletal muscles. On transfection of human rhabdomyosarcoma cell line RD, green fluorescent proteintagged ␤ m resides intracellularly with significant enrichment in nuclear envelopes, whereas ␤ m with transmembrane domain deleted localizes in both cytoplasm and nucleoplasm. Nuclear ␤ m apparently is not in association with Na,K-ATPase because we never detected its ␣-subunit in myonuclear membranes. These results indicate that ␤ m has a specialized function in mammalian perinatal myocytes, different from functions of other X,K-ATPase ␤-subunits. The unique temporospatial distribution of ␤ m protein expression suggests its important role in development of growing skeletal muscle.ATP1B4; sodium, potassium-adenosine 5Ј-triphosphatase; nuclear membrane; skeletal muscle development AMONG MORE THAN 200 P-ATPases identified in prokaryotes and eukaryotes (1), most enzymes have just a single catalytic subunit. However, the animal X,K-ATPases (Na,K-ATPase, gastric H,K-ATPase, and nongastric H,K-ATPase) contain, in addition to the catalytic ␣-subunit, an accessory ␤-subunit. Although major functions such as ATP binding, phosphorylation, and ion transport are performed by the ␣-subunit, the ␣-␤ interaction is required for maturation, stability, and translocation of the ATPases to plasma membrane (4, 44). Moreover, the ␤-subunit seems to be related to K transport, the unique feature of the X,K-ATPase family members (16, 45). The ␤-subunit is involved in K affinity and cardiac glycoside sensitivity (25, 45). Different ␣-and ␤-isoform combinations exhibit functiona...

Evolution of Na,K-ATPase βm-subunit into a coregulator of transcription in placental mammals

“…1a). Transmembrane and C-terminal domains, which contain all structural features of X,K-ATPase ␤-subunits (e.g., a strictly conserved YYPYYGK signature motif), exhibit 48-64% sequence identity that is similar to overall homology of other vertebrate X,K-ATPase ␤-subunit isoforms (4,7). In contrast, sequences of ␤m N-terminal domains are very divergent and specific for each vertebrate class, and only nonadecapeptides adjacent to the transmembrane segments exhibit detectable homology.…”

“…Expression of eutherian ␤m-proteins is confined to skeletal muscle and, at a lower level, to heart and skin (4,6,7) and is strictly developmentally regulated, being the highest in perinatal myocytes (7). For instance, expression of the mouse ATP1B4 gene is induced in the last quarter of pregnancy, but transcripts almost completely disappear within 14 days postpartum (7).…”

“…Eutherian ␤m has all of the structural features and signature motifs specific to X,KATPase ␤-subunits, which are type II integral membrane proteins (4,6,7), and exhibits 30-40% sequence homology with known X,K-ATPase ␤-subunits (4). However, ␤m possesses a unique N-terminal domain containing two long Glu-rich clusters (4,6,7).…”

“…Eutherian ␤m has all of the structural features and signature motifs specific to X,KATPase ␤-subunits, which are type II integral membrane proteins (4,6,7), and exhibits 30-40% sequence homology with known X,K-ATPase ␤-subunits (4). However, ␤m possesses a unique N-terminal domain containing two long Glu-rich clusters (4,6,7). Moreover, in contrast to other family members, which are located at the plasma membrane associated with X,KATPase ␣-subunits, ␤m resides in intracellular stores, being accumulated in nuclear membranes of perinatal myocytes (6)(7)(8).…”

“…However, ␤m possesses a unique N-terminal domain containing two long Glu-rich clusters (4,6,7). Moreover, in contrast to other family members, which are located at the plasma membrane associated with X,KATPase ␣-subunits, ␤m resides in intracellular stores, being accumulated in nuclear membranes of perinatal myocytes (6)(7)(8). Finally, ␤m does not assemble with any of the X,K-ATPase ␣-subunits, thus indicating that it does not function as a subunit of X,K-ATPase in placental mammals (8,9).…”