Our data strongly and logically suggest a

Our data strongly and logically suggest a decreased self-renewal potential in Ptp4a3-KO tumor-initiating Spadin and, in consequence, an inability to form secondary tumors in vivo. The process of tumorigenesis after carcinogen treatment is exceedingly complex and undoubtedly includes the role of stromal cells, including endothelial cells, which are known to express Ptp4a3. However, after identical treatment in vitro, only WT expanded tumor cells and not Ptp4a3-KO expanded tumor cells, were tumorigenic after secondary transplant, suggesting that Ptp4a3 has an important intrinsic function in tumor cells that is necessary for optimal tumorigenicity. This indicates that loss of Ptp4a3 may result in a defect related to the inherent self-renewal potential of tumor-initiating cells. This finding may further explain why Ptp4a3 deficient mice exhibit less colon tumors in the AOM/DSS model of colon cancer and how PTP4A3 may be involved in the metastasis of human colon tumors. The metastatic cascade is dependent on many biological processes and the findings presented here indicate for the first time that PTP4A3 may contribute to metastasis by enhancing the clonogenicity and self-renewal properties of tumor-initiating cells.
Author contributions JC and MZ conceived and designed the study, carried out the experiments, interpreted the data, and wrote the manuscript. TT assisted with experiments and data analysis for in vitro cell culture. GH, JL and EL assisted with experimental design, data analysis, and writing of the manuscript. All authors read and approved the final manuscript.
Acknowledgment This work was supported by NIH grants AA10422 (Homanics), FAA019597 (Zimmerman) and DK085711 (Lagasse). The authors would like to thank Lynda Guzik of the McGowan Institute Flow Cytometry Facility for her technical expertise in FACS.
Introduction Human pluripotent stem cell (hPSC) derived cardiomyocytes (CMs) are proving an invaluable resource for investigating cardiac disease pathology and pharmaceutical evaluation and as a model of human heart development (Burridge et al., 2012; Itzhaki et al., 2011; Matsa et al., 2011; Moretti et al., 2010; Murry and Keller, 2008; Sun et al., 2012). The adult heart contains diverse cell lineages including cardiomyocytes (both atrial and ventricular), smooth muscle cells, endothelial cells, conduction system and interstitial mesenchymal fibroblast cells. Prior work using mouse and human embryonic stem cells (hESCs), which expressed fluorescent proteins driven by the key cardiac transcription factors ISL1 (Bu et al., 2009), MESP1 (Bondue et al., 2011) and NKX2-5 (Elliott et al., 2011), demonstrated that a common precursor can give rise to at least three lineages, cardiomyocytes, smooth muscle and endothelial cells. Nevertheless, development of a detailed cardiovascular cell fate map has been hindered by a lack of cell surface markers to identify, and purify progenitor populations and their mature derivatives (Martin-Puig et al., 2008; Sturzu and Wu, 2011). However, identification of cardiac associated cell surface proteins, such as VCAM1 and SIRPA, provides an opportunity to address this problem (Drukker et al., 2012; Dubois et al., 2011; Elliott et al., 2011; Kattman et al., 2011; Uosaki et al., 2011; Yang et al., 2008). In the mouse, VCAM1 is essential for ventricular myogenesis where it plays a role in mediating myocardial–epicardial communication through interactions with α-4 integrin (Kwee et al., 1995; Yang et al., 1995). Mice lacking VCAM1 die at approximately day 12 of embryogenesis with multiple cardiac lesions including reduced ventricular myocardium, disorganised epicardium and septal defects (Kwee et al., 1995). By contrast, CD34, which marks endothelial precursors (Ferreira et al., 2007), is not required for cardiogenesis, with homozygous null mouse mutants having only mildly impaired haematopoiesis (Cheng et al., 1996). Similarly, heart development proceeds normally in SIRPA knockout mice (Inagaki et al., 2000), consistent with the observation that, unlike in humans, SIRPA does not mark cardiac precursors in the developing mouse (Dubois et al., 2011). Despite appearing to play no functional role in heart development, SIRPA and CD34 are valuable cell surface markers of emerging cardiovascular lineages.