Jakoube, P. | bioRxiv Science

bioRxiv2026

TRANSSULFURATION LINKS ASPARTATE-ASPARAGINE METABOLISM AND REDOX HOMEOSTASIS TO DRIVE TUMOR GROWTH

Cytosolic redox balance is tightly coupled to aspartate synthesis through the malate-aspartate shuttle, and limiting the malate-aspartate shuttle has been proposed to constrain tumor growth by restricting aspartate availability. Here we show that tumors derived from cancer cells lacking GOT1 and GOT2, the cytosolic and mitochondrial aspartate aminotransferases essential for as-partate production and malate-aspartate shuttle function, grow despite impaired canonical as-partate synthesis. This is because cytosolic redox state, not aspartate supply, is the primary metabolic bottleneck in GOT1/GOT2 knockout cells. Using single-cell transcriptomics, metabo-lite tracing, and a loss-of-function CRISPR screen, we find that these tumors engage an adaptive bypass in which availability of asparagine, a product of aspartate, enables serine- and methio-nine-dependent transsulfuration to generate -ketobutyrate, whose reduction regenerates cy-tosolic NAD and restores redox homeostasis. Pharmacological inhibition or genetic ablation of transsulfuration abrogates this asparagine-driven rescue. These findings define asparagine as a regulator of cytosolic NAD/NADH balance and reveal a link between amino acid metabolism and redox control that suggests transsulfuration as a targetable vulnerability in tumor redox maintenance. Significance statementAspartate synthesis and cytosolic redox balance are both coupled through the malate-aspartate shuttle. We show that the cytosolic NAD/NADH ratio, not aspartate supply, is a critical output of the malate-aspartate shuttle for tumor growth. Availability of asparagine, a product of aspar-tate, enables serine- and methionine-dependent transsulfuration to restore cytosolic NAD/NADH balance, proliferation and tumor growth independently of canonical aspartate pro-duction by the malate-aspartate shuttle. This defines asparagine as a regulator of cytosolic re-dox and identifies transsulfuration as a targetable vulnerability in tumor redox maintenance.

cancer biology↗

bioRxiv2025

The role of autoproteolysis and mitoribosomal proteins in regulation of mitochondrial LACTB tumor suppressor

Tumor suppressors represent one of the first lines of defense against malignant transformation and their inactivation in cells leads to onset of tumorigenesis. Cancer cells employ a variety of ways to inactivate cellular tumor suppressors, such as their epigenetic silencing or mutagenesis. Less understood are mechanisms by which cancer cells inactivate tumor suppressors post-translationally. Here, we uncovered a previously undescribed post-translational strategy that cancer cells use to inactivate the potent mitochondrial tumor suppressor LACTB in breast cancers. We discovered that substrate of LACTB can be LACTB itself; that LACTB possesses autoproteolytic ability, which is important for the modulation of its tumor suppressor activity. We show that cancer cells misuse this feature of LACTB to force LACTB into self-degradation. This is mechanistically realized through upregulation of mitochondrial MRPS34 protein, which, through interaction with LACTB, is a positive regulator of the autoproteolytic activity of LACTB and a negative regulator of LACTB. This study, through in vitro, in vivo, human clinical tumor samples and mutagenesis, provides important new insights into how cancer cells fine-tune the expression and activity of tumor suppressors to promote tumorigenesis. Statement of SignificanceWe uncovered a unique post-translational strategy and mechanism cancer cells employ to inactivate the potent mitochondrial tumor suppressor LACTB in breast cancers thus expanding our knowledge on regulatory and adaptive mechanisms cancer cells use to silence tumor suppressors.

cancer biology↗