Characterization of Dendritic Cell-Specific Genes p275 and p306.

Dendritic cells play an inimitable role in the functioning immune system as they are the most potent antigen presenting cells being able to prime naive T-cells. Their characteristic properties that enable them to take up antigens and present them to leukocytes are due to an expression of specific genes and thus specific proteins that are unique to this subset of antigen-presenting cells. Using a substractive cDNA library based on suppression hybridization between DC cDNA and the reference monocyte cDNA, we identified in DC two differentially expressed genes p275 and p306. p275 codes for a membrane protein and represents a splice isoform of the transport protein NAT-1. The predicted structure of protein p306 is globular, suggesting that the protein is either intracellular or secreted. The expression of both genes was confirmed by RT-PCR using cDNA isolated from peripheral blood monocytes and DC, generated in vitro from monocytes or CD34+ progenitor cells. To further analyze the protein expression polyclonal antibodies were generated by immunization with synthetic peptides deduced from the identified sequences. Interestingly, inhibition of DC differentiation using IL-10 or STI571 (Imatinib) resulted in an impaired expression of both proteins. Utilizing specific primers for two recently described splice variants of p306 we identified a new splice form expressed in DC. While the gene of p306 contains eight exons, splice variant 1 consists of the exons 1,2,4,5,6, and 7 and splice variant 2 contains the exons 1,2,3,4,5,6, a shortened exon 7, and exon 8. The new identified splice form includes the exons 1–7. However, as the open reading frame starts in exon 4, the expressed protein is identical with the one corresponding to splice variant 1. Analyzing different DC populations in peripheral blood we show that p306 is expressed in plasmacytoid, but not myeloid DC. Interestingly, the activation of DC with Toll-like receptor ligands (TLRL) Pam3Cys (TLR2L), Poly I:C (TLR3L), LPS (TLR4L) and R848 (TLR7L) has no influence on the expression of p306. Although the functions of p275 and p306 in DC have yet to be determined, both genes play a role in DC differentiation and are found in different hematopoietic cell populations. Especially p306 might be an interesting marker of plasmacytoid DC as the predicted protein does not resemble any known protein structure.