Our present finding furthers this notion and suggests that constitutive or forced expression of GDF3 in melanoma cells links the high CD24 expression accelerating tumor growth. By what mechanism TGF-β-like GDF3 induces up-regulation of CD24 on tumor cells, however, remains unknown. In this regard, ectopic expression of

GDF3 did not promote tumorigenesis of mouse hepatoma G1 and G5 cells. The expression profiles of CD24 in B16 melanoma sublines were parallel to those of GDF3, but hepatoma lines G1 and G5 had impaired the ability to induce Roxadustat in vitro GDF3-mediated CD24 expression. CD24 is rarely expressed on normal cells. Only limited subsets of myeloid cells are CD24-positive [36]. As the signal axis of this GDF3-derived CD24-inducing pathway is undetermined, it remains unsettled as to what is the molecular discrepancy between B16 F1/F10 melanoma cells and G-1/G5 hepatoma cells. Furthermore, the physiological role of the GDF3 signal and its downstream targets has not been elucidated. Yet the GDF3-CD24 pathway frequently turns positive when the cells are malignantly transformed [37] which may support the notion that CD24, when complexed with other see more molecules, alters its function for discrimination of danger signals [37]. Although possible experiments

are in progress, another report suggests that CD24 is associated with Siglec-10 in humans or Siglec-G in mice serve as an innate immune receptor for endogenous self ligands named damage associated molecular pattern (DAMP) [38]. Accumulating evidence indicates that in tumor progression DAMP is released from damaged tissue or tumor cells and modulates both tumor and immune Immune system cells. Recent report suggested that the host inflammatory response to DAMP is partly controlled by a DAMP-CD24-Siglec axis [38]. We favor the speculation that the CD24 signals the presence of DAMP in a tumor micro environment, thereby augmenting inflammatory response to facilitate pathological tumor progression in GDF3-CD24 pathway-positive B16 F1/F10 but not -negative G-1/G-5 cells. Either way, this is the first report on the embryonic antigen GDF3 which is an inducer of CD24 and

joins tumor cell proliferation. Further study may clarify the link between the CD24-Siglec G pathway and innate inflammatory response which occurs in invading tumor and facilitates to establish tumorigenesis. Materials and methods Cell lines and mice B16-F1 and B16-F10 melanoma cells, G1 and G5 hepatoma cells were grown in RPMI1640 with 10% fetal bovine serum. These cell lines were transfectable, and transfection efficiencies were checked using the pEFBOS vector for expression of GFP. The transfection efficiencies were ~25% in F1 and F10 cells and ~20% in G-1 and G-5 cells (data not shown). We tried to establish stable clones constitutively expressing GDF3 in F1 and F10 cells, but failed to establish them. C57BL/6 and BALB/c mice (10-20 weeks of age) were purchased from Hokudo Co. (Sapporo, Japan).