Biology subjects

Porter, L. A.

Publications and source records attributed to Porter, L. A..

6 recordsLinked to original sources

bioRxiv2024

The Cyclin-Like Protein Spy1 Mediates Tumourigenic Potential of Triple Negative Breast Cancer

Triple negative breast cancer is an aggressive subtype of breast cancer that relies on systemic chemotherapy as its primary means of treatment. Cell cycle regulators are enriched in drug resistant forms of the disease supporting the potential of targeting cell cycle checkpoints as a therapeutic direction to re-sensitize patients to treatment. Spy1 is an atypical cyclin-like protein that can override cell cycle checkpoints and is elevated in triple negative breast cancer. We report for the first time the effects of CRISPR-Cas9 mediated knockout of Spy1 on functional characteristics of triple negative breast cancer cells and perform unbiased analysis of protein expression to assess global changes in expression which correlate with functional changes in cell properties. Loss of Spy1 reduced rates of proliferation, decreased metastatic potential, and led to a reduction in stemness properties of triple negative breast cancer cells. Importantly, knockout of Spy1 delayed tumour onset in an in vivo model and significantly increased response to chemotherapy, pushing cells towards a senescent state. This data reveals that changes in expression of proteins that are not essential for proliferation and only transiently expressed can have significant impacts on cell dynamics and provides support for targeting the Spy1-CDK2 complex as a new therapeutic avenue in triple negative breast cancer. Statement of SignificanceTargeting the atypical cell cycle regulator Spy1 induces senescence and increases responsiveness of triple negative breast cancer to standard of care chemotherapy.

cancer biology↗

bioRxiv2024

Atypical Cell Cycle Regulation Promotes Mammary Stem Cell Expansion and Therapeutic Resistance

BackgroundThe cell cycle of mammary stem cells must be tightly regulated to ensure normal homeostasis of the mammary gland to prevent abnormal proliferation and susceptibility to tumorigenesis. The atypical cell cycle regulator, Spy1 can override cell cycle checkpoints, including those activated by the tumour suppressor p53 which mediates mammary stem cell homeostasis. Spy1 has also been shown to promote expansion of select stem cell populations in other developmental systems. Spy1 protein is elevated during proliferative stages of mammary gland development, is found at higher levels in human breast cancers, and promotes susceptibility to mammary tumourigenesis when combined with loss of p53. We hypothesized that Spy1 cooperates with loss of p53 to increase susceptibility to tumour initiation due to changes in susceptible mammary stem cell populations during development and drives the formation of more aggressive stem like tumours. MethodsUsing a transgenic mouse model driving expression of Spy1 within the mammary gland, mammary development and stemness were assessed. These mice were intercrossed with p53 null mice to study the tumourigenic properties of Spy1 driven p53 null tumours, as well as global changes in signaling via RNA sequencing analysis. ResultsWe show that elevated levels of Spy1 leads to expansion of mammary stem cells, even in the presence of p53, and an increase in mammary tumour formation. Spy1-driven tumours have an increased cancer stem cell population, decreased checkpoint signaling, and demonstrate an increase in therapy resistance. Loss of Spy1 decreases tumor onset and reduces the cancer stem cell population. ConclusionsThis data demonstrates the potential of Spy1 to expand mammary stem cell populations and contribute to the initiation and progression of aggressive, drug resistant breast cancers with increased cancer stem cell populations.

cancer biology↗

bioRxiv2023

The ALDH1A3 Reporter Construct: A Novel Mechanism of Identifying and Tracking the Breast Cancer Stem Cell Population

Cancer stem cells lie at the heart of progression and relapse for many solid tumours including breast cancers. The Breast Cancer Stem Cell (BCSC) population is typically isolated via a combination of markers utilizing various staining techniques which prevents the ability to track dynamic changes in expression and to dissect the role in pathogenesis overtime. Here we report the development of a reporter for the expression of Aldehyde Dehydrogenase 1A3 (ALDH1A3), a marker of high clinical importance in many breast cancers, and other solid tumours. BCSCs displaying increased transcriptional activation of ALDH1A3 demonstrate an increase in self-renewal capabilities. This tool improves the ability to reliably follow select cancer stem cell populations over time.

cell biology↗

bioRxiv2022

THE STABILIZATAION OF C-MYC BY THE NOVEL CELL CYCLE REGULATOR, SPY1, DECREASES EFFICACY OF BREAST CANCER TREATMENTS

Purposec-Myc is frequently upregulated in breast cancers, however, targeting c-Myc has proven to be a challenge. Targeting of downstream mediators of c-Myc, such as the cyclin-like cell cycle regulator Spy1, may be a viable therapeutic option in a subset of breast cancer subtypes. MethodsMouse mammary tumour cells isolated from MMTV-Myc mice and human breast cancer cell lines were used to manipulate Spy1 levels followed by tamoxifen or chemotherapeutic treatment with a variety of endpoints. Patient samples from TNBC patients were obtained and constructed into a TMA and stained for c-Myc and Spy1 protein levels. ResultsOver time, MMTV-Myc cells show a decreased response to tamoxifen treatment with increasing levels of Spy1 in the tamoxifen-resistant cells. shRNA against Spy1 re-establishes tamoxifen sensitivity. Spy1 was found to be highly elevated in human TNBC cell and patient samples, correlating to c-Myc protein levels. c-Myc was found to be stabilized by Spy1 and knocking down Spy1 in TNBC cells shows a significant increase in response to chemotherapy treatments. ConclusionsUnderstanding the interplay between protein expression level and response to treatment is a critical factor in developing novel treatment options for breast cancer patients. These data have shown a connection between Spy1 and c-Myc protein levels in more aggressive breast cancer cells and patient samples. Furthermore, targeting c-Myc has proven difficult, these data suggest targeting Spy1 even when c-Myc is elevated can confer an advantage to current chemotherapies.

cancer biology↗

bioRxiv2021

Tuberin levels during cellular differentiation in brain development

Tuberin is a member of a large protein complex, Tuberous Sclerosis Complex, and acts as a sensor for nutrient status regulating protein synthesis and cell cycle progression. Mutations in the Tuberin gene, TSC2, lead to the formation of tumors and developmental defects in many organ systems, including the central nervous system. Tuberin is expressed in the brain throughout development and levels of Tuberin have been found to decrease during neuronal differentiation in cell lines in vitro. Our current work investigates the levels of Tuberin at two stages of embryonic development in vivo, and we study the mRNA and protein levels during a time course using immortalized cell lines in vitro. Our results show that Tuberin levels remain stable in the olfactory bulb but decrease in the Purkinje cell layer during embryonic mouse brain development. We show here that Tuberin levels are higher when cells are cultured as neurospheres, and knockdown of Tuberin results in a reduction in the number of neurospheres. These data provide support for the hypothesis that Tuberin is an important regulator of stemness and the reduction of Tuberin levels might support functional differentiation in the central nervous system. Understanding how Tuberin expression is regulated throughout neural development is essential to fully comprehend the role of this protein in several developmental and neural pathologies. HIGHLIGHTSO_LITuberin protein levels are decreased in the Purkinje cell layer in later stages of embryonic development. C_LIO_LITuberin protein and mRNA levels decrease as cells undergo neuronal differentiation. C_LIO_LIDownregulation of Tuberin impairs neurosphere formation. C_LIO_LITuberin is implicated in the maintenance of stemness in the developing brain. C_LI

developmental biology↗

bioRxiv2019

The Atypical Cyclin-Like Protein Spy1 Overrides p53-Mediated Tumour Suppression and Promotes Susceptibility to Breast Tumorigenesis

Breast cancer is the most common cancer to affect women and one of the leading causes of cancer related deaths. Maintenance of genomic stability and proper regulation of cell cycle checkpoints play a critical role in preventing the accumulation of deleterious mutations. Perturbations in the expression or activity of mediators of cell cycle progression or checkpoint activation represent important events that may increase susceptibility to the onset of carcinogenesis. The atypical cyclin-like protein Spy1 was isolated in a screen for novel genes that could bypass the DNA damage response. Clinical data demonstrates that protein levels of Spy1 are significantly elevated in ductal and lobular carcinoma of the breast. Using a transgenic mouse driving expression of Spy1 in the mammary epithelium we demonstrate that sustained elevation of Spy1 leads to enhanced proliferation and an increased susceptibility to mammary tumour formation. We find that Spy1 is targeted for degradation by the tumour suppressor p53 to protect checkpoint control. When crossed with p53 deficient mice, elevation of Spy1 leads to an increase in hyperplastic alveolar nodules. Targeting cyclin-like protein activity may therefore represent a mechanism of re-sensitizing cells to important cell cycle checkpoints in a therapeutic setting.

cancer biology↗