Expression of the immediate-early response gene IER2 has been associated with the progression of several types of cancer, but its functional role is poorly understood. We found that increased IER2 expression in human melanoma is associated with shorter overall survival, and subsequently investigated the mechanisms through which IER2 exerts this effect. In experimental melanoma models, sustained expression of IER2 induced senescence in a subset of melanoma cells in a p53/MAPK/AKT-dependent manner. The senescent cells produced a characteristic secretome that included high levels of the extracellular phosphoglycoprotein osteopontin. Nuclear localization of the IER2 protein was critical for both the induction of senescence and osteopontin secretion. Osteopontin secreted by IER2-expressing senescent cells strongly stimulated the migration and invasion of non-senescent melanoma cells. Consistently, we observed coordinate expression of IER2, p53/p21, and osteopontin in primary human melanomas and metastases, highlighting the pathophysiological relevance of IER2-mediated senescence in melanoma progression. Together, our study reveals that sustained IER2 expression drives melanoma invasion and progression through stimulating osteopontin secretion via the stochastic induction of senescence.

ASAP1 is a multi-domain adaptor protein that regulates cytoskeletal dynamics, receptor recycling and intracellular vesicle trafficking. Its expression is associated with poor prognosis for a variety of cancers, and promotes cell migration, invasion and metastasis. Little is known about its physiological role. In this study, we used mice with a gene-trap inactivated ASAP1 locus to study the functional role of ASAP1 in vivo, and found defects in tissues derived from mesenchymal progenitor cells. Loss of ASAP1 led to growth retardation and delayed ossification typified by enlarged hypertrophic zones in growth plates and disorganized chondro-osseous junctions. Furthermore, loss of ASAP1 led to delayed adipocyte development and reduced fat depot formation. Consistently, deletion of ASAP1 resulted in accelerated chondrogenic differentiation of mesenchymal cells in vitro, but suppressed osteo- and adipogenic differentiation. Mechanistically, we found that FAK/Src and PI3K/AKT signaling is compromised in Asap1^GT/GT MEFs, leading to impaired adipogenic differentiation. Dysregulated FAK/Src and PI3K/AKT signaling is also associated with attenuated osteogenic differentiation. Together these observations suggest that ASAP1 plays a decisive role during the differentiation of mesenchymal progenitor cells. Mesenchymal progenitor cells are capable of differentiating into a number of lineages including osteoblasts, chondrocytes and adipocytes, and have therefore attracted interest for their potential application in regenerative medicine. Furthermore, defects in mesenchymal progenitor cell differentiation are considered to contribute to various diseases including metabolic syndrome, obesity and osteoporosis. In this study, we analyzed mice deficient in the multi-adaptor protein ASAP1, which has been implicated in tumor progression and metastasis. These mice display growth retardation, and a delayed development of bone and fat tissue. Consistently, mesenchymal progenitor cells deficient in ASAP1 exhibited enhanced differentiation into chondrocytes, but impaired differentiation into adipocytes and osteoblasts. Together these observations suggest that ASAP1 plays a decisive role during the differentiation of mesenchymal stem cells, which may be relevant for a number of diseases such as cancer.

VEGFR-3 is a transmembrane receptor tyrosine kinase that is activated by its ligands VEGF-C and VEGF-D. Although VEGFR-3 has been linked primarily to the regulation of lymphangiogenesis, in the present study, we demonstrate a role for VEGFR-3 in megakaryopoiesis. Using a human erythroleukemia cell line and primary murine BM cells, we show that VEGFR-3 is expressed on megakaryocytic progenitor cells through to the promegakaryoblast stage. Functionally, specific activation of VEGFR-3 impaired the transition to polyploidy of CD41⁺ cells in primary BM cultures. Blockade of VEGFR-3 promoted endoreplication consistently. In vivo, long-term activation or blockade of VEGFR-3 did not affect steady-state murine megakaryopoiesis or platelet counts significantly. However, activation of VEGFR-3 in sublethally irradiated mice resulted in significantly elevated numbers of CD41⁺ cells in the BM and a significant increase in diploid CD41⁺ cells, whereas the number of polyploid CD41⁺ cells was reduced significantly. Moreover, activation of VEGFR-3 increased platelet counts in thrombopoietin-treated mice significantly and modulated 5-fluorouracil–induced thrombocytosis strongly, suggesting a regulatory role for VEGFR-3 in megakaryopoiesis.

We have recently demonstrated that the anthocyanidin delphinidin (DEL), one of the most abundant dietary flavonoids, inhibits activation of ErbB and vascular endothelial growth factor receptor family members. These receptors play crucial roles in the context of tumor progression and the outgrowth of blood and lymphatic vessels. Here, we have developed an improved chemical synthesis for DEL in order to study the effects of the aglycon and its degradation product gallic acid (GA) on endothelial and tumor cells in vitro and in vivo . We found that DEL blocked the proliferation in vitro of primary human blood and lymphatic endothelial cells as well as human HT29 colon and rat MT-450 mammary carcinoma cells in a dose-dependent manner. In contrast, its degradation product GA had little effect. At higher concentrations, DEL induced apoptosis of endothelial and tumor cells. Furthermore, DEL potently blocked the outgrowth of lymphatic capillaries in ex vivo lymphangiogenesis assays. In the MT-450 rat syngeneic breast tumor model, it also significantly reduced angiogenesis and tumor-induced lymphangiogenesis when administered in vivo . These data reveal DEL to be a novel antilymphangiogenesis reagent. Surprisingly, however, the application of DEL unexpectedly promoted tumor growth and metastasis in the MT-450 tumor model, suggesting that the antiproliferative effect of DEL on cultured cells does not necessarily reflect the response of tumors to this anthocyanidin in vivo . Furthermore, while DEL may have utility as a cancer chemopreventative agent, its ability to promote tumor growth once a neoplasm develops also needs to be taken into consideration.