||Dlk is a transmembrane protein that possesses six epidermal growth factor-like sequences at the extracellular domain, a single transmembrane domain and an intracellular tail. The extracellular EFG-like region of Dlk can be released by action of an unknown protease that cuts the extracellular region near the cell membrane. Dlk belongs to the EGF-like homeotic protein family and has received many names: pG2, FA-1, Pref-1, SCP-1, ZOG and Dlk. All the proteins are identical or polymorphic products of a single gene. Dlk has been involved in several differentiation processes, such as adipogenesis, hematopoiesis and neuroendocrine differentiation. Dlk is also known as the preadipocyte factor-1 (Pref-1), is highly expressed in preadipocytes but is completely abolished in adipocytes. Pref-1 may function in the maintenance of the preadipocyte state and is a negative regulator of adipocyte differentiation.|
Dlk is expressed in tumors with neuroendocrine features, such as human neuroblastoma, rat pheochromocytoma, and a subset of Small Cell Lung Cancer (SCLC) cell lines. The Dlk expression is probably associated with some differentiation stages because the most undifferentiated cells were lacking expression of Dlk. The finding suggests that Dlk plays an important role in differentiation and tumorigenesis of several cell types.
The study was designed to examine the influence of dlk overexpression on tumorigenicity of hepatoma cells. We constructed the mammalian expression vectors for full-length dlk, dlk extracellular domain, which were transfected into SK-Hep-1 cells for generation of stable clones. The transgene expressions in selected stable clones were verified by QRT-PCR and western blot analysis. Our results indicated that overexpression of extracellular domain significantly promoted the viability of SK-Hep1 cells during serum deprivation. In SCID mice, injection of full-length dlk clones led to increased tumor growth compared with the control groups. However, the migration ability was reduced in Dlk stable clones. In summary, these results suggested full-length Dlk promoted the tumor growth but reduced the migration ability of SK-Hep1 cells.