MICU2, a Paralog of MICU1, Resides within the Mitochondrial Uniporter Complex to Regulate Calcium Handling

Abstract

Mitochondrial calcium uptake is present in nearly all vertebrate tissues and is believed to be critical in shaping calcium signaling, regulating ATP synthesis and controlling cell death. Calcium uptake occurs through a channel called the uniporter that resides in the inner mitochondrial membrane. Recently, we used comparative genomics to identify MICU1 and MCU as the key regulatory and putative pore-forming subunits of this channel, respectively. Using bioinformatics, we now report that the human genome encodes two additional paralogs of MICU1, which we call MICU2 and MICU3, each of which likely arose by gene duplication and exhibits distinct patterns of organ expression. We demonstrate that MICU1 and MICU2 are expressed in HeLa and HEK293T cells, and provide multiple lines of biochemical evidence that MCU, MICU1 and MICU2 reside within a complex and cross-stabilize each other's protein expression in a cell-type dependent manner. Using in vivo RNAi technology to silence MICU1, MICU2 or both proteins in mouse liver, we observe an additive impairment in calcium handling without adversely impacting mitochondrial respiration or membrane potential. The results identify MICU2 as a new component of the uniporter complex that may contribute to the tissue-specific regulation of this channel.

The EF-Hand Ca2+ Binding Protein MICU Choreographs Mitochondrial Ca2+ Dynamics in Arabidopsis

“…This indicates that, although diversification can occur, one MICU locus is sufficient and Arabidopsis represents this minimal configuration. Furthermore, homologs of the MICU1 isoforms MICU2 and 3 that are present in vertebrates (Plovanich et al, 2013; could not be found in Arabidopsis. The amino acid sequence of Arabidopsis MICU (At-MICU; AT4G32060; predicted splicing variant 1: At-MICU.1) showed 45% similarity and 25% identity to its homolog in human.…”

“…Use of closely related models, including mouse and a variety of different human and other mammalian cell lines, can hamper a clear distinction of fundamental, conserved players and mechanisms from variation within the mammalian class, species, or even cell lines. For instance, three MICU isoforms of distinct function operate in mammalian cells, necessitating a complex working model of MCU regulation (Plovanich et al, 2013). Yet, the number of MICU homologs varies in eukaryotes, pointing to a specific situation in mammals that cannot be straightforwardly generalized to other Figure 8A for more images) to illustrate the overrepresentation of mitochondria with translucent matrices in the micu lines.…”

“…The recent identification of several protein families making up the mitochondrial Ca 2+ uniporter complex (MCUC) in mammals, including the pore-forming MCU (MCU and MCUb;Baughman et al, 2011;De Stefani et al, 2011;Raffaello et al, 2013), and the regulatory, associated MICUs (MICU1, 2, and 3; Perocchi et al, 2010;Plovanich et al, 2013), EMRE (Sancak et al, 2013), and MCUR1/CCDC90A (although potentially not directly; Mallilankaraman et al, 2012b;Paupe et al, 2015), has spurred intense research across the biomedical disciplines Mallilankaraman et al, 2012a;Csordás et al, 2013;Hoffman et al, 2013;Marchi et al, 2013;Pan et al, 2013;Raffaello et al, 2013;Kovács-Bogdán et al, 2014;Logan et al, 2014;Patron et al, 2014;Wang et al, 2014). While some genes of the complex components appear not to be present in plants (e.g., MCUb and EMRE), others have multiple homologs (six for the functional poreforming subunit MCU in Arabidopsis [Stael et al, 2012] and maize [Zea mays; Meng et al, 2015] and two for MCUR1/CCDC90A in Arabidopsis), suggesting potential functional modification and/or differentiation.…”

Ion and inhibitor binding of the double-ring ion selectivity filter of the mitochondrial calcium uniporter

“…Among them, the single-pass transmembrane (TM) protein EMRE (Essential MCU REgulator) is absolutely required for the MCU to conduct ions (8). Two soluble components in the intermembrane space, MICU1 and MICU2, are Ca 2+ -sensing proteins that gate the activity of MCU based on outside Ca 2+ concentrations through EMRE (9)(10)(11)(12). The current consensus is that the minimum requirements for uniporter-mediated Ca 2+ flux in metazoans are MCU and EMRE, whereas in lower organisms such as Dictyostelium that lack EMRE, MCU is able to operate (13).…”

Metabolic Syndrome in Aging Heart: Molecular Insights

“…The most important contributor to Mito Ca 2+ uptake is the mitochondrial calcium uniporter complex (MCUC) with the MCU serving as a highly selective channel that moves Ca 2+ ions across the IMM dependent on Mito membrane potential (ΔΨm). Recently, integrative genomics methods enabled the discovery of the molecular nature of MCU, and its regulatory subunits, MCUb, MICU1 and 2, and EMRE [22][23][24][25][26][27]. MCU is an integral membrane protein with two transmembrane domains that forms the pore through which Mito Ca 2+ currents are conducted across the IMM [22,23].…”