Characterization of the structural requirements and cell type specificity of IL-1 alpha and IL-1 beta secretion.

The murine macrophage cell line, P388D1, was transfected with expression plasmids containing a cDNA for the precursor or mature form of human interleukin (IL)-1 alpha or -1 beta, and the extent of IL-1 protein secretion was analyzed. The secretion of IL-1 beta from cells transfected with a cDNA encoding the mature IL-1 beta was approximately 15-fold greater than from cells transfected with a precursor IL-1 beta cDNA. Although P388D1 cells transfected with precursor and mature IL-1 alpha cDNAs exhibited similar levels of secretion, the precursor IL-1 alpha cDNA-transfected cells secreted only the mature form of IL-1 alpha. Relatively high levels of IL-1 secretion were also observed in cultures of HeLa cells and the murine EL 4 and human Jurkat T cell lines that were transfected with a mature IL-1 alpha or -beta expression plasmid. Secretion was not observed when these cell lines were transfected with precursor IL-1 alpha or -beta expression plasmids. Secretion was also minimal when P388D1 cells were transfected with cDNAs encoding mature IL-1 beta proteins lacking the NH2- or COOH-terminal 20 amino acids. These results indicate that the mature forms of IL-1 proteins are the preferred substrates for secretion and that the maintenance of a specific conformation of these proteins may be required for optimal secretion.