Expression of Hepatoma-derived growth factor family members in the adult central nervous system

HDGF was rather evenly expressed throughout all brain regions tested with the lowest expression in the substantia nigra. HRP-2 was strongly expressed in the thalamus, prefrontal and parietal cortex, neurohypophysis, and the cerebellum, HRP-3 in the bulbus olfactorius, piriform cortex and amygdala complex. HDGF and HRP-2 were found to be expressed by neurons, astrocytes and oligodendrocytes. In contrast, strong expression of HRP-3 in the adult nervous system is restricted to neurons, except for very weak expression in oligodendrocytes in the brain stem. Although the majority of neurons are HRP-3 positive, some like cerebellar granule cells are negative.The coexpression of HDGF and HRP-2 in glia and neurons as well as the coexpression of all three proteins in many neurons suggests different functions of members of the HDGF protein family in cells of the central nervous system that might include proliferation as well as cell survival. In addition the restricted expression of HRP-3 point to a special function of this family member for neuronal cells.The family of Hepatoma derived growth factor (HDGF) and HDGF related proteins (HRPs) comprises six members which belong to different subgroups according to their length and isoelectric points. [1]. Little is known about the function of the different family members. So far, most studies addressed HDGF which was initially purified from the supernatant of human hepatoma cell lines [2,3].Five HDGF homologous proteins have been identified so far [1,4,5]. Four of these proteins have been termed HRP-1 to -4 (HDGF Related Proteins 1 to 4), the fifth p52/75 or LEDGF (Lens Epithelium-derived growth factor). HDGF and its homologues display between 54% and 78% sequence identity among the 91 N-terminal amino acids. Because of this similarity the amino-terminal region has been termed Homologue to Amino Terminus of HDGF (HATH region [4]). In contrast, the length and amino acid sequence of HRP's C-terminal regions vary suggesting a modular