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Open Access Publications from the University of California

Scholarly Works (39 results)

  • Article
  • Peer Reviewed
Lawrence Berkeley National Laboratory (2008)
    Cover page: Is CD133 a marker of metastatic colon cancer stem cells?
    • Article
    • Peer Reviewed
    Lawrence Berkeley National Laboratory (2007)
      Cover page: Of Microenvironments and Mammary Stem Cells
      • Article
      • Peer Reviewed
      Lawrence Berkeley National Laboratory (2008)
        Cover page: Human mammary progenitor cell fate decisions are products of interactions with combinatorial microenvironments
        • Thesis
        • Peer Reviewed
        UC Berkeley Electronic Theses and Dissertations (2016)

        Breast cancer alone accounts for 29 % of all new cancer diagnoses and is the second leading cause of cancer related death. Improvement in early detection and the understanding of oncogenic drivers connected to malignant transformation and cancer progression has lead to an overall decrease in breast cancer related mortality1. However, therapeutic durability remains a problem for both chemotherapies and pathway-targeted drugs. Furthermore, the poor translation from pre-clinical screening results to clinical outcomes impedes therapeutic development.

        Genomic heterogeneity and other cell intrinsic mechanisms are commonly examined as a major source of therapeutic failure. Using a reductionist approach, I examined the hypothesis that the tissue microenvironment is a potent modulator of drug activity and therapeutic response. I first tested the hypothesis that matrix rigidity of microenvironments can modulate the efficacy of the targeted-therapeutic small molecule, lapatinib, in HER2-amplified breast cancer cell lines. The anti-proliferative effect of lapatinib was inversely proportional to the elastic modulus of the adhesive substrates. The modulus-dependent lapatinib responses were eliminated with treatment of mechanosensing inhibitors, Y27632 and blebbistatin. Knockdown of the hippo pathway mechanotransducer, YAP, eliminated the modulus-dependent lapatinib responses, and pharmacological inhibition of YAP phenocopied the effect of YAP knockdown. Reduction of YAP in vivo in mice also slowed the growth of implanted HER2-amplified tumors, these showing a trend of increasing sensitivity to lapatinib as YAP decreased. Thus, I addressed the role of stiffness in resistance to, and efficacy of, a HER2 pathway-targeted therapeutic via the mechanotransduction arm of the hippo pathway.

        In order to dissect and investigate the microenvironmental impact on drug responses, we developed the MicroEnvironmental microarray, (MEArray) platform. The method allows for simultaneous control of the molecular composition and the elastic modulus. Utilizing the MEArray, I further tested the hypothesis that in addition to matrix rigidity, molecular composition can modulate lapatinib responses. I systematically quantified the microenvironmental impact on cellular morphological changes and the lapatinib responses. The results were consistent with our previous report that matrix rigidity conferred lapatinib resistance. I also identified that cells adhered to fibronectin showed higher lapatinib resistance independent of stiffness. The validations showed that fibronectin conferred nuclear YAP translocation, which may explain partly the mechanism of the lapatinib resistance. Further studies for elucidation of fibronectin-induced lapatinib resistance are needed. However, simultaneous modulation of stiffness and molecular composition revealed a continuum of drug responses resulting from cell-microenvironment interactions.

          Cover page: Dissection of the impact of tissue context on anti-cancer drug activity through the use of high dimensional combinatorial microenvironment analysis
          • Article
          • Peer Reviewed
          LBL Publications (2016)
          Age is the greatest risk factor for breast cancer, but the reasons underlying this association are unclear. While there is undeniably a genetic component to all cancers, the accumulation of mutations with age is insufficient to explain the age-dependent increase in breast cancer incidence. In this viewpoint, we propose a multilevel framework to better understand the respective roles played by somatic mutation, microenvironment, and epigenetics making women more susceptible to breast cancer with age. The process of aging is associated with gradual breast tissue changes that not only corrupt the tumor-suppressive activity of normal tissue but also impose age-specific epigenetic changes that alter gene expression, thus reinforcing cellular phenotypes that are associated with a continuum of age-related tissue microenvironments. The evidence discussed here suggests that while the riddle of whether epigenetics drives microenvironmental changes, or whether changes in the microenvironment alter heritable cellular memory has not been solved, a path has been cleared enabling functional analysis leading to the prediction of key nodes in the network that link the microenvironment with the epigenome. The hypothesis that the accumulation of somatic mutations with age drives the age-related increase in breast cancer incidence, if correct, has a somewhat nihilistic conclusion, namely that cancers will be impossible to avoid. Alternatively, if microenvironment-driven epigenetic changes are the key to explaining susceptibility to age-related breast cancers, then there is hope that primary prevention is possible because epigenomes are relatively malleable.
            Cover page: Breast Cancer beyond the Age of Mutation
            • Article
            • Peer Reviewed
            UC San Francisco Previously Published Works (2018)
            The biology of aging is challenging to study, particularly in humans. As a result, model organisms are used to approximate the physiological context of aging in humans. However, the best model organisms remain expensive and time-consuming to use. More importantly, they may not reflect directly on the process of aging in people. Human cell culture provides an alternative, but many functional signs of aging occur at the level of tissues rather than cells and are therefore not readily apparent in traditional cell culture models. Organoids have the potential to effectively balance between the strengths and weaknesses of traditional models of aging. They have sufficient complexity to capture relevant signs of aging at the molecular, cellular, and tissue levels, while presenting an experimentally tractable alternative to animal studies. Organoid systems have been developed to model many human tissues and diseases. Here we provide a perspective on the potential for organoids to serve as models for aging and describe how current organoid techniques could be applied to aging research.
              Cover page: Opportunities for organoids as new models of aging
              • Article
              • Peer Reviewed
              UC San Francisco Previously Published Works (2012)
              Variability in signaling pathway activation between neighboring epithelial cells can arise from local differences in the microenvironment, noisy gene expression, or acquired genetic changes. To investigate the consequences of this cell-to-cell variability in signaling pathway activation on coordinated multicellular processes such as morphogenesis, we use DNA-programmed assembly to construct three-dimensional MCF10A microtissues that are mosaic for low-level expression of activated H-Ras. We find two emergent behaviors in mosaic microtissues: cells with activated H-Ras are basally extruded or lead motile multicellular protrusions that direct the collective motility of their wild-type neighbors. Remarkably, these behaviors are not observed in homogeneous microtissues in which all cells express the activated Ras protein, indicating that heterogeneity in Ras activity, rather than the total amount of Ras activity, is critical for these processes. Our results directly demonstrate that cell-to-cell variability in pathway activation within local populations of epithelial cells can drive emergent behaviors during epithelial morphogenesis.
                Cover page: Programmed Cell-to-Cell Variability in Ras Activity Triggers Emergent Behaviors during Mammary Epithelial Morphogenesis
                • Article
                • Peer Reviewed
                UC Berkeley Previously Published Works (2013)
                Abstract Background Shortening of telomeres, which are essential for maintenance of genomic integrity, is a mechanism commonly associated with the aging process. Here we ascertained whether changes in telomere lengths or telomerase activity correlated with age in normal human mammary epithelial cells (HMEC), or with phenotypes of aging in breast. Accordingly, flow cytometry fluorescence in situ hybridization (flowFISH) was used to determine relative telomere lengths (RTL), and telomerase activity was measured by the telomeric repeat amplification protocol (TRAP), in a collection of 41 primary HMEC strains established from women aged 16 to 91 years. Results RTL measurements of HMEC strains that were heterogeneous with respect to lineage composition revealed no significant associations between telomere length with age, maximum observed population doublings, or with lineage composition of the strains. However, within strains, luminal epithelial and cKit-expressing epithelial progenitor cells that were flow cytometry-enriched from individual HMEC strains exhibited significantly shorter telomeres relative to isogenic myoepithelial cells (P < 0.01). In unsorted strains, detectable telomerase activity did not correlate with RTL. Telomerase activity declined with age; the average age of strains that exhibited TRAP activity was 29.7 ± 3.9y, whereas the average age of strains with no detectable TRAP activity was 49.0 ± 4.9y (P < 0.01). Non-detectable TRAP activity also was correlated with phenotypes of aging previously described in HMEC strains; increased proportions of CD227-expressing luminal epithelial cells (P < 0.05) and cKit-expressing progenitor cells (P < 0.05). Conclusions Telomere shortening did not correlate with the chronological ages of HMEC strains, whereas decreased telomerase activity correlated with age and with lineage distribution phenotypes characteristic of aging.
                  Cover page: Aging phenotypes in cultured normal human mammary epithelial cells are correlated with decreased telomerase activity independent of telomere length
                  • Article
                  • Peer Reviewed
                  LBL Publications (2019)
                  Preventing breast cancer before it is able to form is an ideal way to stop breast cancer. However, there are limited existing options for prevention of breast cancer. Changes in the breast tissue resulting from the aging process contribute to breast cancer susceptibility and progression and may therefore provide promising targets for prevention. Here, we describe new potential targets, immortalization and inflammaging, that may be useful for prevention of age-related breast cancers. We also summarize existing studies of warfarin and metformin, current drugs used for non-cancerous diseases, that also may be repurposed for breast cancer prevention.
                    Cover page: Breast Tissue Biology Expands the Possibilities for Prevention of Age-Related Breast Cancers
                    • Article
                    • Peer Reviewed
                    UC Berkeley Previously Published Works (2017)
                    Exposures to various DNA damaging agents can deregulate a wide array of critical mechanisms that maintain genome integrity. It is unclear how these processes are impacted by one's age at the time of exposure and the complexity of the DNA lesion. To clarify this, we employed radiation as a tool to generate simple and complex lesions in normal primary human mammary epithelial cells derived from women of various ages. We hypothesized that genomic instability in the progeny of older cells exposed to complex damages will be exacerbated by age-associated deterioration in function and accentuate age-related cancer predisposition. Centrosome aberrations and changes in stem cell numbers were examined to assess cancer susceptibility. Our data show that the frequency of centrosome aberrations proportionately increases with age following complex damage causing exposures. However, a dose-dependent increase in stem cell numbers was independent of both age and the nature of the insult. Phospho-protein signatures provide mechanistic clues to signaling networks implicated in these effects. Together these studies suggest that complex damage can threaten the genome stability of the stem cell population in older people. Propagation of this instability is subject to influence by the microenvironment and will ultimately define cancer risk in the older population.
                      Cover page: Lesion complexity drives age related cancer susceptibility in human mammary epithelial cells
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