Biology subjects

Sessions, G. A.

Publications and source records attributed to Sessions, G. A..

3 recordsLinked to original sources

bioRxiv2026

Non-Genetic Mechanisms of Fractional Resistance to Abemaciclib in Dedifferentiated Liposarcoma.

Dedifferentiated liposarcoma is a rare mesenchymal malignancy driven by amplification of chromosome 12q13-15, which includes the oncogenes CDK4 and MDM2. CDK4 amplification provides a rationale for targeted therapy with CDK4/6 inhibitors, and abemaciclib has shown the most durable activity reported to date in this disease. Clinical responses, however, are incomplete and often transient, and the cellular features that allow tumor cells to continue proliferating during treatment are not well understood. To address this gap, we performed multiplexed single-cell imaging to quantify 17 cell-cycle regulators in both dedifferentiated liposarcoma cell line Lipo246 and surgically resected primary human cells exposed to abemaciclib. Both models contained a subpopulation of cells that retained phosphorylated retinoblastoma protein, a marker of cell proliferation, at the highest abemaciclib doses. These fractionally resistant cells were defined by selective enrichment of cyclin-dependent kinase 2 (CDK2), cyclin B1, and phosphorylated ribosomal protein S6 (pS6), and showed enhanced sensitivity to the CDK2 inhibitor, tagtociclib. Together, these findings reveal nongenetic cell cycle plasticity as a mechanism of escape from CDK4/6 inhibition in dedifferentiated liposarcoma and nominate CDK2 and the PI3K-mTOR pathway as candidate targets for combination therapy.

cancer biology↗

bioRxiv2024

Multiplexed single-cell imaging reveals diverging subpopulations with distinct senescence phenotypes during long-term senescence induction.

Cellular senescence is a phenotypic state that contributes to the progression of age-related disease through secretion of pro-inflammatory factors known as the senescence associated secretory phenotype (SASP). Understanding the process by which healthy cells become senescent and develop SASP factors is critical for improving the identification of senescent cells and, ultimately, understanding tissue dysfunction. Here, we reveal how the duration of cellular stress modulates the SASP in distinct subpopulations of senescent cells. We used multiplex, single-cell imaging to build a proteomic map of senescence induction in human epithelial cells induced to senescence over the course of 31 days. We map how the expression of SASP proteins increases alongside other known senescence markers such as p53, p21, and p16INK4a. The aggregated population of cells responded to etoposide with an accumulation of stress response factors over the first 11 days, followed by a plateau in most proteins. At the single-cell level, however, we identified two distinct senescence cell populations, one defined primarily by larger nuclear area and the second by higher protein concentrations. Trajectory inference suggested that cells took one of two discrete molecular paths from unperturbed healthy cells, through a common transitional subpopulation, and ending at the discrete terminal senescence phenotypes. Our results underscore the importance of using single-cell proteomics to identify the mechanistic pathways governing the transition from senescence induction to a mature state of senescence characterized by the SASP.

cell biology↗

bioRxiv2020

The combination of mitogenic stimulation and cell cycle arrest induces senescence in equine and human cartilage explants

ObjectiveCellular senescence is a phenotypic state characterized by stable cell-cycle arrest, enhanced lysosomal activity, and the secretion of inflammatory molecules and matrix degrading enzymes. Senescence has been implicated in osteoarthritis (OA) pathophysiology; however, the mechanisms that drive senescence induction in cartilage and other joint tissues are unknown. While numerous physiological signals are capable of initiating the senescence phenotype, one emerging theme is that growth-arrested cells convert to senescence in response to sustained mitogenic stimulation. The goal of this study was to develop an in vitro articular cartilage explant model to investigate the mechanisms of senescence induction. DesignThis study utilized healthy articular cartilage derived from cadaveric equine stifles and human ankles. Explants were irradiated or treated with palbociclib to initiate cell cycle arrest, and mitogenic stimulation was provided by serum-containing medium (horse) and the inclusion of growth factors (human). The primary readout of senescence was a quantitative flow cytometry assay to detect senescence-associated {beta} galactosidase activity (SA-{beta}-gal). ResultsIrradiation of equine explants caused 25.39% of cells to express high levels of SA-{beta}-gal, as compared to 3.82% in control explants (p=0.0031). For human cartilage, explants that received both mitogenic stimulation and cell cycle arrest showed increased rates of senescence induction as compared to baseline control (7.16% vs. 2.34% SA-{beta}-gal high, p=0.0007). ConclusionsTreatment of cartilage explants with mitogenic stimuli in the context of cell-cycle arrest reliably induces high levels of SA-{beta} gal activity, which provides a physiologically relevant model system to investigate the mechanisms of senescence induction.

cell biology↗