Abstract 5428: Detachment from the extracellular matrix induces loss of the mitochondrial phosphatase PGAM5 in cancer cells

Abstract Cancer cells often experience altered mitochondrial metabolism due to loss of integrin-mediated attachment to the extracellular matrix (ECM). Relatedly, work from our lab has revealed that ECM-detached cells undergo mitophagy, which subsequently results in the activation of cell death pathways. Cancer cells, however, can circumvent the induction of mitophagy during ECM-detachment to promote their viability, however, the mechanisms underlying mitophagy regulation during ECM-detachment remain poorly understood. The mitochondrial phosphatase PGAM5 is a part of a proteinaceous complex that initiates mitophagy during ECM-detachment, but its regulation in this context has not been extensively studied. Interestingly, we find that certain cancer cell lines have an innate ability to reduce the levels of PGAM5 protein when cultured under ECM-detached conditions. We find that this phenomenon is primarily due to alterations in PGAM5 transcription, rather than from alterations in protein stability. Given that ECM-detachment has been previously shown to impair proliferation, we analyzed PGAM5 expression in ECM-attached cells treated with CDK4/6 inhibitors. Our data suggest that expression of PGAM5 is indeed linked to proliferation, as arresting cells in G1 results in decreased PGAM5 expression. We also examined the consequences of reduced PGAM5 on mitochondrial dynamics. Previous research has discovered that PGAM5 dephosphorylates Drp1, a key regulator of mitochondrial fission. Indeed, we observe that decreased expression of PGAM5 (both during ECM-detachment and after treatment with CDK4/6 inhibitors) results in elevated phosphorylation of Drp1, suggesting an increase in mitochondrial fusion in detached and G1 arrested cells are likely. These data collectively support the conclusion that ECM-detachment causes changes in mitochondrial dynamics as a consequence of impaired proliferation and subsequent loss of PGAM5. Citation Format: Matthew Fink, Zachary Schafer. Detachment from the extracellular matrix induces loss of the mitochondrial phosphatase PGAM5 in cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5428.