The importance of calcium in the body has been stressed to many of us from childhood, and for good reason. Calcium is the most abundant mineral in the body, and its functions range from promoting tooth and bone health to enabling muscle contraction, neuron signaling, blood clotting, and hormone release. Calcium is a crucial intermediate for compartmentalized signaling pathways that control cell growth and viability. For example, calcium activates the tricarboxylic acid (TCA) cycle, an important cascade of energy-producing reactions in the mitochondria. This function and others keep cells healthy and growing, but sudden influxes of calcium to the mitochondria can also trigger cell death. Thus, to balance the calcium-controlled energy production and signaling reactions necessary for life with the looming threat of calcium-induced cell death, mitochondrial calcium abundance must be tightly regulated.
Fibrolamellar carcinoma (FLC) is a rare liver cancer that primarily affects young people. Currently, the only way to cure FLC is to surgically remove the tumor, but this is only effective if the cancer has not spread to distant sites. In advanced cases where surgery is not an option, no standard of care currently exists, highlighting the need for more effective FLC treatments. One way in which FLC cells differ from normal liver cells is their higher mitochondrial content. This unique phenotype drew Dr. Yasemin Sancak, a mitochondrial biologist, to more closely interrogate what could be happening with FLC mitochondria. “Beyond [the high mitochondrial content], I also noticed that the mitochondria in the cancer have a lot of calcium deposits,” says Sancak of the early stages of the project, “so…this is actually interesting.” Basically, researchers might be able to exploit the extra mitochondria and calcium deposits to develop new treatments for FLC patients—but first, they have to figure out why they are in FLC cells in the first place.
Changes in mitochondrial calcium levels are associated with metabolic disorders, neurodegeneration, and cancers, but the precise reasons for these changes have eluded researchers. To fill this knowledge gap, Sancak and her team set off to investigate how mitochondrial calcium could impact cancer progression. Calcium is imported into mitochondria through a channel called the uniporter, so the team created a uniporter knockout (KO) cell line to test how inhibiting calcium import would affect cancer cells. They found that uniporter KO cells proliferated much slower than cells with intact uniporters. To figure out why the lack of mitochondrial calcium would lead to slow proliferation, Sancak and her team analyzed the proteins and RNA transcripts that were different between cells with and without the uniporter. They found that genes and proteins involved in branched-chain amino acid (BCAA) catabolism were enriched in the uniporter-KO cells. BCAA catabolism is a metabolic pathway that breaks down specific types of amino acids to be converted into energy. When cells perform less BCAA catabolism, they can conserve their BCAAs as materials for proteins to build new cells. For cancers like FLC, the group hypothesized that the high calcium levels observed in FLC cells could lead to less BCAA catabolism, leaving more building blocks so that the cancer cells can divide and propagate disease.
To test this hypothesis, they measured the expression of the previously identified BCAA catabolism genes in normal liver tissue and FLC tumors. Unsurprisingly, the FLC tumor samples showed a significant decrease in BCAA catabolism gene expression. This suggests that increased mitochondrial calcium metabolically reprograms FLC cells to decrease BCAA catabolism and promote cancer growth, but still the precise link between calcium and BCAA catabolism gene transcription remained unclear.
In the liver, the transcription factor KLF15 controls the expression of many metabolic pathways, including BCAA catabolism. The group found that FLC tumors express much less KLF15 compared to normal liver samples. When the group knocked down the calcium uniporter in mouse liver cells, they found that KLF15 levels increased significantly. Together, these results indicate that mitochondrial calcium levels control KLF15 levels. In turn, KLF15 abundance controls the expression of BCAA catabolism genes.
“FLC has one of the extreme [cancer metabolic signatures] where you see this strong inhibition of BCAA catabolism,” notes Sancak, “and I think calcium is all linked to it.” Before the work of Sancak and her colleagues, no group had previously identified a link between calcium signaling and BCAA catabolism. While this work is focused on FLC, the authors highlight that roughly 70% of cancers exhibit reduced BCAA catabolism. KLF15 abundance is also associated with cancer growth and poor patient outcomes across cancer types. In the future, the group plans to explore how these mechanisms apply to other types of liver cancer and explore ways to therapeutically exploit increased mitochondrial calcium.
This work was supported by the National Institutes of Health, the National Science Foundation, the Department of Defense, the Pew Charitable Trusts, the Fibrolamellar Foundation, and the University of Washington EDGE Center.
Fred Hutch/UW/Seattle Children’s Cancer Consortium members Drs. Yasemin Sancak, Lucas Sullivan, Shao-En Ong, John D. Scott, and Raymond S. Yeung contributed to this work.
Marsh NM, MacEwen MJS, Chea J, Kenerson HL, Kwong AA, Locke TM, Miralles FJ, Sapre T, Gozali N, Hart ML, Bammler TK, MacDonald JW, Sullivan LB, Atilla-Gokcumen GE, Ong S, Scott JD, Yeung RS, Sancak Y. 2025. Mitochondrial calcium signaling regulates branched-chain amino acid catabolism in fibrolamellar carcinoma. Sci Adv. 11(22):eadu9512. doi: 10.1126/sciadv.adu9512
Kelsey Woodruff is a PhD candidate in the Termini Lab at Fred Hutch Cancer Center. She studies how acute myeloid leukemia cells remodel the sugars on their membranes to reprogram cancer cell signaling. Originally from Indiana, she holds a bachelor's degree in Biochemistry from Ball State University. Outside of lab, you can find her crocheting and enjoying the Seattle summers.
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