Biology subjects

Holtzen, S. E.

Publications and source records attributed to Holtzen, S. E..

3 recordsLinked to original sources

bioRxiv2026

Metal homeostasis is remodeled in response to different quiescence triggers

Cells can enter a reversible non-proliferative state called quiescence either spontaneously or in response to nutrient deprivations. Metal ions are essential nutrients and play wide-ranging regulatory and signaling roles in biological processes. We previously showed that zinc is an essential nutrient for the mammalian cell cycle as zinc deprivation drives cells into quiescence, and this quiescent state is associated with changes in iron, copper, and manganese, suggesting broad remodeling of metal homeostasis. Here we examine whether metal remodeling is a general feature of quiescence by inducing quiescence via different triggers (zinc deficiency, serum starvation, and growth factor withdrawal) in MCF10A cells. Fluorescence microscopy and elemental analysis reveal significant trigger-dependent changes in the labile and total metal pools of quiescent cells. To gain insight into these differences, we carried out RNA sequencing and differential expression analysis, focusing on metal associated, metal regulatory, and metal homeostasis genes. While core quiescence pathways are shared across triggers, quiescence states remain molecularly distinct. A significant percent of 2458 metal homeostasis annotated genes are differentially expressed including 55% in starvation-induced quiescence, 50% in zinc deficiency-induced quiescence and 21% in growth factor withdrawal-induced quiescence. Our results also showed unique alteration of genes involved in major metal dependent processes including antioxidant activity, oxidative phosphorylation, heme metabolism, and chromatin accessibility in different quiescence states. Overall, this work demonstrates that metal homeostasis is systematically rewired during cellular quiescence with associated effects on genes that regulate critical biological processes. Significance StatementCells constantly evaluate their nutrient and energy status and integrate these signals into proliferation-quiescence decisions. Quiescence prevents cells from passing damage to daughter cells. Metals are essential micronutrients for biological processes. While limitation of zinc can drive cells into quiescence and alter other metals, how metals are remodeled and whether this is a common feature of quiescence was unknown. Here we examined three quiescence triggers by modifying growth media and serum, the primary source of metals. We report significant changes in labile and total Cu, Fe, Zn and Mn pools, and metal associated genes in response to distinct quiescence triggers. These changes converge on mitochondrial function, cellular antioxidant activity, and heme biosynthesis in a trigger specific manner.

cell biology↗

bioRxiv2025

Systematic characterization of zinc in a series of breast cancer cell lines reveals significant changes in zinc homeostasis

An optimal amount of labile zinc (Zn2+) is essential for proliferation of human cells, where Zn2+ levels that are too high or too low cause cell cycle exit. Tumors of the breast have been characterized by high levels of total Zn2+. Given the role of Zn2+ in proliferation of human cells and elevation of zinc in breast cancer tumors, we examined the concentration of total and labile Zn2+ across a panel of 5 breast cancer cell lines, compared to the normal MCF10A cell line. We found that three cell lines (MDA-MB-231, MDA-MB-157, and SK-Br-3) showed elevated labile Zn2+ in the cytosol, while T-47D showed significantly lower Zn2+, and MCF7 showed no change compared to MCF10A cells. There was no change in total Zn2+ across the cell lines, as measured by ICP-MS, but we did observe a difference in the cells ability to accumulate Zn2+ when Zn2+ in the media was elevated. Therefore, we examined how proliferation of each cell line was affected by increases and decreases in the media. We found striking differences, where three cancer cell lines (MDA-MB-231, MDA-MB-157, and MCF7) showed robust proliferation in high Zn2+ at concentrations that killed MCF10A, T-47D, and SK-Br-3 cells. We also discovered that 4 of the 5 cancer cell lines demonstrate compromised proliferation and increased cell death in low Zn2+, suggesting these cells may be addicted to Zn2+. Overall, our study suggests significant differences in Zn2+ homeostasis and regulation in different types of breast cancer cells, with consequences for both proliferation and cell viability.

cell biology↗

bioRxiv2023

Transient Zn2+ deficiency induces replication stress and compromises daughter cell proliferation

Cells must replicate their genome quickly and accurately, and they require metabolites and cofactors to do so. Ionic zinc (Zn2+) is an essential micronutrient that is required for hundreds of cellular processes, including DNA synthesis and adequate proliferation. Deficiency in this micronutrient impairs DNA synthesis and inhibits proliferation, but the mechanism is unknown. Using fluorescent reporters to track single cells via long-term live-cell imaging, we find that Zn2+ is required at the G1/S transition and during S-phase for timely completion of S-phase. A short pulse of Zn2+ deficiency impairs DNA synthesis and increases markers of replication stress. These markers of replication stress are reversed upon resupply of Zn2+. Finally, we find that if Zn2+ is removed during the mother cells S-phase, daughter cells enter a transient quiescent state, maintained by sustained expression of p21, which disappears upon reentry into the cell cycle. In summary, short pulses of mild Zn2+ deficiency in S-phase specifically induce replication stress, which causes downstream proliferation impairments in daughter cells. SignificanceZinc is an essential micronutrient required for cells to grow and proliferate. However, the mechanism of how zinc influences proliferation is unknown. We show that short exposure to mild zinc deficiency in S-phase impairs DNA synthesis and induces replication stress, leading to pauses in daughter cell proliferation. However, pulses of low zinc during other phases of the cell cycle dont affect mother cell cycle progression or daughter cell proliferation. These results indicate that while zinc is important for many proteins, during the cell cycle short pulses of mild zinc deficiency have the biggest impact on a cells ability to synthesize DNA, suggesting that DNA polymerase complex acts as a gate keeper, sensing zinc status in the cell.

cell biology↗