Metabolic adaptation to the chronic loss of Ca2+ signaling induced by KO of IP3 receptors or the mitochondrial Ca2+ uniporter

Abstract

Calcium signaling is essential for regulating many biological processes. Endoplasmic reticulum inositol trisphosphate receptors (IP 3 Rs) and the mitochondrial Ca 2+ uniporter (MCU) are key proteins that regulate intracellular Ca 2+ concentration. Mitochondrial Ca 2+ accumulation activates Ca 2+ -sensitive dehydrogenases of the tricarboxylic acid (TCA) cycle that maintain the biosynthetic and bioenergetic needs of both normal and cancer cells. However, the interplay between calcium signaling and metabolism is not well understood. In this study, we used human cancer cell lines (HEK293 and HeLa) with stable KOs of all three IP 3 R isoforms (triple KO [TKO]) or MCU to examine metabolic and bioenergetic responses to the chronic loss of cytosolic and/or mitochondrial Ca 2+ signaling. Our results show that TKO cells (exhibiting total loss of Ca 2+ signaling) are viable, displaying a lower proliferation and oxygen consumption rate, with no significant changes in ATP levels, even when made to rely solely on the TCA cycle for energy production. MCU KO cells also maintained normal ATP levels but showed increased proliferation, oxygen consumption, and metabolism of both glucose and glutamine. However, MCU KO cells were unable to maintain ATP levels and died when relying solely on the TCA cycle for energy. We conclude that constitutive Ca 2+ signaling is dispensable for the bioenergetic needs of both IP 3 R TKO and MCU KO human cancer cells, likely because of adequate basal glycolytic and TCA cycle flux. However, in MCU KO cells, the higher energy expenditure associated with increased proliferation and oxygen consumption makes these cells more prone to bioenergetic failure under conditions of metabolic stress.

Calcium homeostasis and cancer: insights from endoplasmic reticulum-centered organelle communications

“…The involvement of MAM in regulating cell proliferation is exemplified by ER-resident IP3R (as discussed earlier) and additionally by mitochondrial VDAC1 in lung cancer [25] and the MCU in colorectal cancer [26,27]. Dysregulated Ca 2+ homeostasis has been shown to promote cell proliferation with a high energy expenditure, which provides potential vulnerable targets in cancer cells under metabolic stress [24,28].…”

“…The low-level, constitutive Ca 2+ transfer from ER to mitochondria is critical for cancer cell survival and proliferation [22,23]. Mitochondrial Ca 2+ accumulation activates Ca 2+ -sensitive dehydrogenases of the tricarboxylic acid cycle and is thus critical for the biosynthetic and bioenergetic needs of cancer cells [23,24]. The involvement of MAM in regulating cell proliferation is exemplified by ER-resident IP3R (as discussed earlier) and additionally by mitochondrial VDAC1 in lung cancer [25] and the MCU in colorectal cancer [26,27].…”

Shaped by leaky ER: Homeostatic Ca2+ fluxes

“…However, there is also MCU-independent Ca 2+ uptake to mitochondria ( Garbincius and Elrod, 2022 ). For instance, in MCU knockout cells, agonist-induced increase in m Ca 2+ is strongly reduced, or even abolished ( Young et al, 2022 ; Álvarez-Illera et al, 2020 ). However, m Ca 2+ oscillations can be MCU-independent, at least in C. elegans ( Álvarez-Illera et al, 2020 ).…”

The mitochondrial Ca2+channel MCU is critical for tumor growth by supporting cell cycle progression and proliferation

“…A distinction between that study and the present one is the former examined the acute effects of MCU knockdown whereas the present studies used cells with MCU stably deleted. Similarly, acute knockdown of InsP3R caused cancer cell death (Cardenas et al, 2010;Cardenas et al, 2016), whereas stable deletion of all InsP3R was associated with a significantly repressed proliferative capacity (Young et al, 2022). Compensatory mechanisms have been proposed to account for the lack of overt physiological consequences of MCU-KO in mice of mixed genetic backgrounds (Garbincius et al, 2020).…”

“…Destabilization of the interaction between MCU and MICU1 led to increased cell proliferation and tumor growth of lung cancer (Marchi et al, 2019), yet silencing of MICU1 in ovarian cancer cells enhanced sensitivity to cell-death stimuli and decreased cell migration (Chakraborty et al, 2017). Whereas genetic deletion of InsP3R in HEK293 and HeLa cells was found to generate a bioenergetic crisis associated with reduced cell proliferation, genetic deletion of MCU failed to phenocopy this effect (Young et al, 2022). Thus, the roles of ER-to-mitochondria Ca 2+ transfer in cancer remain unclear.…”