Hepatoma Derived Growth Factor (HDGF) is the original member of a family of polypeptides designated HDGF-related proteins (HRPs). HDGF was initially characterized as a secreted mitogen from the Huh-7 human hepatoma cell line. This nuclear targeted vascular smooth muscle cell mitogen (VSM) is a heparin-binding protein that is highly expressed in tumor cells where it stimu-lates proliferation. HDGF is also reported to be involved in organ development and lung remodeling after injury by promoting proliferation of lung epithelial cells. During development, HDGF expression is high in the nucleus and cytoplasm of smooth muscle and endothelial cells. The HRP (HDGF related proteins) family contains four proteins, HRP-1, HRP-2, HRP-3 and HRP-4. HRP-1 and HRP-4 are only expressed in testis while HRP-2 is widely expressed in different tissues. HRP-3 can solely be found in the nervous system. Specif-ically it is strongly expressed in bulbus, olfactorius, piriform cortex and amygdala complex while HRP-2 in brain is located in the thalamus, prefrontal and parietal cortex, neurohypophysis, and the cerebellum. In the central nervous system, HRP proteins play a role in neuron proliferation and cell survival.