The cellular microenvironment comprises soluble factors, support cells, and components of the extracellular matrix (ECM) that combine to regulate cellular behavior. Pluripotent stem cells utilize interactions between support cells and soluble factors in the microenvironment to assist in the maintenance of self-renewal and the process of differentiation. However, the ECM also plays a significant role in shaping the behavior of human pluripotent stem cells, including embryonic stem cells (hESCs) and induced pluripotent stem cells. Moreover, it has recently been observed that deposited factors in a hESC-conditioned matrix have the potential to contribute to the reprogramming of metastatic melanoma cells. Therefore, the ECM component of the pluripotent stem cell microenvironment necessitates further analysis.In this study we first compared the self-renewal and differentiation properties of hESCs grown on Matrigel™ pre-conditioned by hESCs to those on unconditioned Matrigel™. We determined that culture on conditioned Matrigel™ prevents differentiation when supportive growth factors are removed from the culture medium. To investigate and identify factors potentially responsible for this beneficial effect, we performed a defined SILAC MSbased proteomics screen of hESC-conditioned Matrigel™. From this proteomics screen, we identified over 80 extracellular proteins in matrix conditioned by hESCs and induced pluripotent stem cells. These included matrixassociated factors that participate in key stem cell pluripotency regulatory pathways, such as Nodal/Activin and canonical Wnt signaling. This work represents the first investigation of stem-cell-derived matrices from human pluripotent stem cells using a defined SILAC MS-based proteomics approach. Molecular & Cellular Proteomics

Numerous matrices for the growth of human embryonic stem cells (hESC) in vitro have been described. However, their exact composition is typically unknown. Information on the components of these matrices will aid in the development of a fully defined growth surface for hESCs. These matrices typically consist of mixture of proteins present in a wide range of abundance making their characterization challenging. In this study, we performed the proteomic analysis of five previously uncharacterized matrices: CellStart, Human Basement Membrane Extract (Human BME), StemXVivo, Bridge Human Extracellular Matrix (BridgeECM), and mouse embryonic fibroblast conditioned matrix (MEF-CMTX). Based on a proteomics protocol optimized using lysates from HeLa cells, we undertook the analysis of the five complex extracellular matrix (ECM) samples using a combination of strong anion and cation exchange chromatography and SDS-PAGE. For each of these matrices, we identify numerous proteins, indicating their complex nature. We also compared these results with a similar proteomics analysis of the growth matrix, Matrigel™. From these analyses, we observed that fibronectin is a primary component of nearly all hESC supportive matrices. This observation led to the investigation of the suitability of fibronectin as a defined ECM for the growth of hESCs. We found that fibronectin promotes the maintenance of pluripotent H9 and CA1 hESCs in an undifferentiated state using mTeSR1 medium. This finding validates the utility of characterizing matrices used for hESC growth in revealing ECM components required for culturing hESCs in a universally applicable defined system.

Recent evidence points to extra-telomeric, noncanonical roles for telomerase in regulating stem cell function. In this study, human embryonic stem cells (hESCs) were cultured in 20% or 2% O 2 microenvironments for up to 5 days and evaluated for telomerase reverse transcriptase (TERT) expression and telomerase activity. Results showed increased cell survival and maintenance of the undifferentiated state with elevated levels of nuclear TERT in 2% O 2 -cultured hESCs despite no significant difference in telomerase activity compared with their high-O 2 -cultured counterparts. Pharmacological inhibition of telomerase activity using a synthetic tea catechin resulted in spontaneous hESC differentiation, while telomerase inhibition with a phosphorothioate oligonucleotide telomere mimic did not. Reverse transcription polymerase chain reaction (RT-PCR) analysis revealed variations in transcript levels of full-length and alternate splice variants of TERT in hESCs cultured under varying O 2 atmospheres. Steric-blocking of Da and Db hTERT splicing using morpholino oligonucleotides altered the hTERT splicing pattern and rapidly induced spontaneous hESC differentiation that appeared biased toward endomesodermal and neuroectodermal cell fates, respectively. Together, these results suggest that posttranscriptional regulation of TERT under varying O 2 microenvironments may help regulate hESC survival, selfrenewal, and differentiation capabilities through expression of extra-telomeric telomerase isoforms.

Lymphatic metastasis is a common occurence in breast cancer. Molecular mechanisms in breast cancer-associated lymphangiogenesis and lymphatic metastasis are poorly defined. We had earlier shown that elevated cyclo-oxygenase (COX)-2 expression by human as well as murine breast cancer cells promotes tumor progression and metastasis by multiple mechanisms: inactivation of host anti-tumor immune cells, stimulation of tumor cell migration and tumor-associated angiogenesis. Furthermore, COX-2 was causally associated with increased VEGF-C expression/secretion in human and murine breast cancer cell lines, thus promoting tumor-associated lymphangiogenesis. VEGF-C production was partially dependent on endogenous PGE-2 mediated activation of EP4 receptors on breast cancer cells thus making EP4 a good therapeutic target. It was unclear whether tumor or host derived PGE-2 had any direct effect on lymphangiogenesis, and if so, whether EP4 receptors on lymphatic endothelial cells played any role. To address these questions, we devised an in vitro lymphangiogenesis assay using a LYVE-1 expressing rat mesenteric lymphatic endothelial cell line (RMLEC) plated on growth factor- reduced Matrigel. Endothelial tube formation by RMLEC was rapidly induced in 12-18 hours after plating on Matrigel even under serum-free conditions, whereas plating them on collagen gel even in the presence of serum did not induce any tube formation. This suggested the presence of some inducing factor(s) in the Matrigel, possibly also present in the ECM in vivo. Matrigel-induced tube formation was completely abrogated in the presence of COX 1/2 inhibitor indomethacin (10mM), COX-2 inhibitor NS-398 (15mM), and a selective EP4 antagonist CJ-042794 (2.5 mM). In each case, an additional presence of PGE2 (1 µM) or an EP4 agonist PGE-1 alcohol (1µM) completely restored the tube formation on matrigel. A similar restoration was also achieved in the presence of serum-free conditioned media (24 h culture) of a COX-2 expressing murine breast cancer cell line C3L5 that induces lymphangiogenesis in vivo. These results indicate the roles of tumor as well as host-derived PGE2 in inducing lymphangiogenesis possibly by activating COX-2/EP4 receptors on lymphatic endothelial cells. Further studies are in progress to identify the tube-inducing component(s) in the Matrigel and C3L5 cell conditioned medium. (Supported by grants from the Canadian Breast Cancer Foundation, Ontario chapter and the Ontario Institute of Cancer Research to PKL. The gift of the RMLEC from Dr Sophia Ran, Southern Illinois Univ School of Medicine is gratefully acknowledged). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 636.

Morpholino oligonucleotides (MO) are an innovative tool that provides a means for examining and modifying gene expression outcomes by antisense interaction with targeted RNA transcripts. The site-specific nature of their binding facilitates focused modulation to alter splice variant expression patterns. Here we describe the steric-blocking of human telomerase reverse transcriptase (hTERT) Δα and Δβ splice variants using MO to examine cellular outcomes related to pluripotency and differentiation in human embryonic stem cells.