Preliminary Research On CCP22 Function

The TGFβ(transforming growth factorβ)-Smads cell signaling pathway plays important roles in cell proliferation, apoptosis and differentiation. TGFβsignaling is initiated by ligand binding to the transmembrane receptor serine-threonine kinase TGF-βreceptor. The ligand-activated receptor phosphorylates receptor-regulated Smads (R-Smads), including Smad2 and Smad3 in TGFβsignaling, thereby promoting their open conformation. In this state, these receptor-activated Smads can form complexes with a common mediator Smad, Smad4, and translocate to the nucleus, where they bind DNA and regulate transcription of TGFβresponsive target genes. Alterations in Smad2 and Smad4 genes have been found to associate with many types of human cancers, and thus Smads are considered to be important tumor suppressors. Numerous transcription factors and coregulators have been recently identified to interact with Smads and regulate the signaling outcome. However, the intracellular signaling pathways modulating TGFβresponsive gene expression are not fully elucidated.The complement control protein module (CCP) distributes widely. The CCP-containing proteins play important roles in complement control, clearance of modified cells, remove of microorganisms, and tumor development and progression. Till now, more than one hundred CCP-containing proteins have been identified.Using Smad4 MH2 domain as bait in yeast two-hybrid system, we isolated from a normal human mammary library a novel gene, named CCP22, as a Smad4 interacting protein. CCP22 was expressed in many cell lines and tissues. CCP22 has two endogenous fragments, designated CCP22-N and CCP22-C. both of which physically interacted with Smad4. CCP22 interacted with 325-514 aa of Smad4 MH2 domain.CCP22 can affect the transcriptional activity of Smads. Decreasing the expression level of CCP22 increased the transcription of some downstream reporter genes of TGFβ/Smads, including p15-Luc, p21-Luc and 3-TP-Luc. Decreasing the expression of CCP22 also increased the expression of some TGFβ-responsive genes such as p15 and p21.CCP22 can regulate cancer cell proliferation. Knocking down CCP22 expression with CCP22 siRNA inhibited the growth rate of some cancer cells, including breast cancer and lung cancer cells.Cancer cells features anchor-independent cell growth determined by soft agar assay. Decreasing the expression of CCP22 nagatively affected anchor-independent growth of some kinds of cancer cells.In conclusion, CCP22 plays a negative role in the regulation of TGFβ/Smads signaling pathway, and can regulate cancer cell proliferation. CCP22 may become a new target of anti-tumor therapy.