John Landua

Texas A&M University System Health Science Center, Bryan, Texas, United States

Are you John Landua?

Claim your profile

Publications (9)41.4 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Cancer stem cells (CSCs, or tumor-initiating cells) may be responsible for tumor formation in many types of cancer, including breast cancer. Using high-resolution imaging techniques, we analyzed the relationship between a Wnt-responsive, CSC-enriched population and the tumor vasculature using p53-null mouse mammary tumors transduced with a lentiviral Wnt signaling reporter. Consistent with their localization in the normal mammary gland, Wnt-responsive cells in tumors were enriched in the basal/myoepithelial population and generally located in close proximity to blood vessels. The Wnt-responsive CSCs did not colocalize with the hypoxia-inducible factor 1α-positive cells in these p53-null basal-like tumors. Average vessel diameter and vessel tortuosity were increased in p53-null mouse tumors, as well as in a human tumor xenograft as compared with the normal mammary gland. The combined strategy of monitoring the fluorescently labeled CSCs and vasculature using high-resolution imaging techniques provides a unique opportunity to study the CSC and its surrounding vasculature.
    STEM CELLS TRANSLATIONAL MEDICINE 05/2014; · 3.60 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In breast cancer, a subset of tumor-initiating cells (TIC) or “cancer stem cells” are thought to be responsible for tumor maintenance, treatment resistance, and disease recurrence. While current breast cancer stem cell markers (e.g. CD44high/CD24low/neg, ALDH positive) have allowed enrichment for such cells, they are not universally expressed, and may actually identify distinct TIC subpopulations in the same tumor. Thus, additional markers of functional stem cells are needed. The STAT3 pathway is a critical regulator of the function of normal stem cells, and evidence is accumulating for its important role in breast cancer stem cells. However, due to the lack of a method for separating live cells based on their level of STAT3 activity, it remains unknown whether STAT3 functions in the cancer stem cells themselves, or in surrounding niche cells, or in both. To approach this question, we constructed a series of lentiviral fluorescent (Enhanced Green Fluorescent Protein, EGFP) reporters that enabled flow cytometric enrichment of cells differing in STAT3-mediated transcriptional activity, as well as in vivo/in situ localization of STAT3 responsive cells. Using in vivo claudin-low cell line xenograft models of human breast cancer, we found that STAT3 signaling reporter activity (EGFP+) is associated with a subpopulation of cancer cells enriched for mammosphere-forming efficiency, as well as TIC function in limiting dilution transplantation assays compared to negative or unsorted populations. Our results support STAT3 signaling activity as another functional marker for human breast cancer stem cells thus making it an attractive therapeutic target for stem-cell-directed therapy in some breast cancer subtypes. Stem Cells 2014
    Stem Cells 05/2014; · 7.70 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Our goal was to gain a better understanding of the contribution of the burial of polar groups and their hydrogen bonds to the conformational stability of proteins. We measured the change in stability, Δ(ΔG), for a series of hydrogen bonding mutants in four proteins: villin head piece subdomain (VHP) containing 36 residues, a surface protein from Borrelia burgdorferi (VlsE) containing 341 residues, and two proteins previously studied in our laboratory, ribonucleases Sa (RNase Sa) and T1 (RNase T1). Crystal structures were determined for three of the hydrogen bonding mutants of RNase Sa: S24A, Y51F, and T95A. The structures are very similar to wild type RNase Sa and the hydrogen bonding partners form intermolecular hydrogen bonds to water in all three mutants. We compare our results with previous studies of similar mutants in other proteins and reach the following conclusions. 1. Hydrogen bonds contribute favorably to protein stability. 2. The contribution of hydrogen bonds to protein stability is strongly context dependent. 3. Hydrogen bonds by side chains and peptide groups make similar contributions to protein stability. 4. Polar group burial can make a favorable contribution to protein stability even if the polar groups are not hydrogen bonded. 5. The contribution of hydrogen bonds to protein stability is similar for VHP, a small protein, and VlsE, a large protein.
    Protein Science 03/2014; · 2.74 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The vasculature inside breast cancers is one important component of the tumour microenvironment. The investigation of its spatial morphology, distribution and interactions with cancer cells, including cancer stem cells, is essential for elucidating mechanisms of tumour development and treatment response. Using confocal microscopy and fluorescent markers, we have acquired three-dimensional images of vasculature within mammary tumours and normal mammary gland of mouse models. However, it is difficult to segment and reconstruct complex vasculature accurately from the in vivo three-dimensional images owing to the existence of uneven intensity and regions with low signal-to-noise ratios (SNR). To overcome these challenges, we have developed a novel three-dimensional vasculature segmentation method based on local clustering and classification. First, images of vasculature are clustered into local regions, whose boundaries well delineate vasculature even in low SNR and uneven intensity regions. Then local regions belonging to vasculature are identified by applying a semi-supervised classification method based on three informative features of the local regions. Comparison of results using simulated and real vasculature images, from mouse mammary tumours and normal mammary gland, shows that the new method outperforms existing methods, and can be used for three-dimensional images with uneven background and low SNR to achieve accurate vasculature reconstruction.
    Interface focus: a theme supplement of Journal of the Royal Society interface 08/2013; 3(4):20130015. · 2.21 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The analysis of normal mammary morphogenesis is facilitated by the use of mammary fat pad transplantation. The recent experiments on analysis of normal mammary epithelial stem cell activity rely heavily on this technique. In this review, we discuss the known and unknown attributes of using Matrigel in the injection of the mammary epithelial cell suspension. Matrigel greatly increases the "take" frequency of the injected cell suspension; however, there is some uncertainty regarding the interpretation of some of the results. After consideration of these issues, our conclusion is that Matrigel is important in order to obtain rigorous and reproducible results.
    Journal of Mammary Gland Biology and Neoplasia 05/2012; 17(2):99-101. · 7.52 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Our goal was to gain a better understanding of the contribution of hydrophobic interactions to protein stability. We measured the change in conformational stability, Δ(ΔG), for hydrophobic mutants of four proteins: villin headpiece subdomain (VHP) with 36 residues, a surface protein from Borrelia burgdorferi (VlsE) with 341 residues, and two proteins previously studied in our laboratory, ribonucleases Sa and T1. We compared our results with those of previous studies and reached the following conclusions: (1) Hydrophobic interactions contribute less to the stability of a small protein, VHP (0.6±0.3 kcal/mol per -CH(2)- group), than to the stability of a large protein, VlsE (1.6±0.3 kcal/mol per -CH(2)- group). (2) Hydrophobic interactions make the major contribution to the stability of VHP (40 kcal/mol) and the major contributors are (in kilocalories per mole) Phe18 (3.9), Met13 (3.1), Phe7 (2.9), Phe11 (2.7), and Leu21 (2.7). (3) Based on the Δ(ΔG) values for 148 hydrophobic mutants in 13 proteins, burying a -CH(2)- group on folding contributes, on average, 1.1±0.5 kcal/mol to protein stability. (4) The experimental Δ(ΔG) values for aliphatic side chains (Ala, Val, Ile, and Leu) are in good agreement with their ΔG(tr) values from water to cyclohexane. (5) For 22 proteins with 36 to 534 residues, hydrophobic interactions contribute 60±4% and hydrogen bonds contribute 40±4% to protein stability. (6) Conformational entropy contributes about 2.4 kcal/mol per residue to protein instability. The globular conformation of proteins is stabilized predominantly by hydrophobic interactions.
    Journal of Molecular Biology 03/2011; 408(3):514-28. · 3.91 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Interactions between cancer cells and factors within the tumor microenvironment (mE) are essential for understanding tumor development. The spatial relationships between blood vessel cells and cancer cells, e.g. tumor initiating cells (TICs), are an important parameter. Accurate segmentation of blood vessel is necessary for the quantization of their spatial relationships. However, this remains an open problem due to uneven intensity and low signal to noise ratio (SNR). To overcome these challenges, we propose a novel approach that integrates an oriented hidden Markov random field model (Ori-HMRF) with local clustering. The local clustering delineates boundaries of blood vessel segments with low SNR. Then blood vessel segments are viewed as random variables in the Ori-HMRF and their spatial dependence is defined based on directional information. The Ori-HMRF model suppresses noise and generates accurate blood vessel segmentation results. Experimental validations were conducted on both normal mammary and breast cancer tissues.
    IEEE International Conference on Bioinformatics and Biomedicine, BIBM 2011, Atlanta, GA, USA, 12-15 November, 2011; 01/2011
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Whole mount preparations of mouse mammary glands are useful for evaluating overall changes in growth and morphology, and are essential for detecting and evaluating focal or regionally-localized phenotypes that would be difficult to detect or analyze using other techniques. We present three newly developed methods for preparing whole mounts of mammary glands from genetically-engineered mice expressing fluorescent proteins, as well as using either neutral red or a variety of fluorescent dyes. Unlike traditional hematoxylin- or carmine-stained preparations, neutral red-stained and some fluorescent preparations can be used for several common downstream analyses.
    Journal of Mammary Gland Biology and Neoplasia 11/2009; 14(4):411-5. · 7.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Systemic hormones and local growth factor-mediated tissue interactions are essential for mammary gland development. Using phenotypic and transplantation analyses of mice carrying the mesenchymal dysplasia (mes) allele of patched 1 (Ptch1mes), we found that Ptch1mes homozygosity led to either complete failure of gland development, failure of post-pubertal ductal elongation, or delayed growth with ductal dysplasia. All ductal phenotypes could be present in the same animal. Whole gland and epithelial fragment transplantation each yielded unique morphological defects indicating both epithelial and stromal functions for Ptch1. However, ductal elongation was rescued in all cases, suggesting an additional systemic function. Epithelial function was confirmed using a conditional null Ptch1 allele via MMTV-Cre-mediated disruption. In Ptch1mes homozygotes, failure of ductal elongation correlated with diminished estrogen and progesterone receptor expression, but could not be rescued by exogenous ovarian hormone treatment. By contrast, pituitary isografts were able to rescue the ductal elongation phenotype. Thus, Ptch1 functions in the mammary epithelium and stroma to regulate ductal morphogenesis, and in the pituitary to regulate ductal elongation and ovarian hormone responsiveness.
    Development 01/2009; · 6.21 Impact Factor

Publication Stats

150 Citations
41.40 Total Impact Points

Institutions

  • 2011–2014
    • Texas A&M University System Health Science Center
      • Molecular and Cellular Medicine
      Bryan, Texas, United States
  • 2009
    • Baylor College of Medicine
      Houston, Texas, United States