Control of lysosomal-mediated cell death by the pH-dependent calcium channel RECS1

Abstract

RECS1, a member of the TMBIM family, triggers lysosomal membrane permeabilization in cells undergoing lysosomal stress.

TMBIM5 loss of function alters mitochondrial matrix ion homeostasis and causes a skeletal myopathy

“…Ca 2+ binding of BsYetJ is inhibited by K + and Na + ions (Guo et al, 2019), suggesting that other ions may compete for Ca 2+ and might be transported by BsYetJ and therefore possibly also by TMBIM5. These findings imply nonselective ion transport properties of TMBIM proteins, a feature recently described for the lysosomal TMBIM1 (also known as RECS1 [Zhao et al, 2006]) channel that can flux Ca 2+ as well as Na + (Pih án et al, 2021). Mutation of the di-aspartyl motif abolishes the Ca 2+ flux properties of both TMBIM6 (Bultynck et al, 2012) and TMBIM1 (Pih án et al, 2021).…”

“…We mutated two highly conserved negatively charged aspartate residues in the presumed pore domain ( Fig S1 ) to neutral arginine residues. These residues were chosen because their mutation abolishes channel function in the homologous proteins TMBIM6/BI-1 ( Bultynck et al, 2012 ) and TMBIM1/RECS1 ( Pihán et al, 2021 ) as well as in the bacterial orthologue BsYetJ ( Guo et al, 2019 ). Overexpression of TMBIM5 D294R/D325R (DM) was not able to increase ATP-evoked mitochondrial Ca 2+ uptake to the same levels as overexpressing wild-type TMBIM5, implying that these aspartate residues partially disrupt TMBIM5 function, and most likely its channel activity ( Fig 2D ).…”

“…The prokaryotic TMBIM5 orthologue BsYetJ can be inhibited by K + and Na + ions within the physiological range ( Guo et al, 2019 ). In addition, another TMBIM family member, TMBIM1, can also transport Na + in addition to Ca 2+ ( Pihán et al, 2021 ). Together, these results imply that TMBIM proteins might be nonselective ion channels that gate Ca 2+ only under specific conditions and that other ions could influence their Ca 2+ transport properties.…”

“…We decided to disrupt the channel-lining di-aspartyl motif and altered the polarity of the negatively charged aspartic acid at position 326 (corresponding to human D325) which lines the presumed channel pore of TMBIM5 and all other TMBIM proteins, including the prokaryotic BsYetJ ( Chang et al, 2014 ; Lisak et al, 2015 ) ( Fig S1 ). This amino acid is essential for the Ca 2+ channel activity of TMBIM6 ( Bultynck et al, 2012 ) and BsYetJ ( Chang et al, 2014 ), as well as the Ca 2+ and Na + channel activity of TMBIM1 ( Pihán et al, 2021 ). We replaced the aspartic acid residue with a basic arginine by CRISPR/Cas9–mediated germline mutagenesis in C57BL/6 mice, generating the C57BLB/6J-Ghitm em1(D326R)LTK line, here called TMBIM5 D326R.…”

“…These findings imply nonselective ion transport properties of TMBIM proteins, a feature recently described for the lysosomal TMBIM1 (also known as RECS1 [Zhao et al, 2006]) channel that can flux Ca 2+ as well as Na + (Pih án et al, 2021). Mutation of the di-aspartyl motif abolishes the Ca 2+ flux properties of both TMBIM6 (Bultynck et al, 2012) and TMBIM1 (Pih án et al, 2021). Together these homologies suggest a role for TMBIM5 in mitochondrial Ca 2+ transport and ion homeostasis, which we decided to investigate in vitro and in vivo.…”