POSTTRANSCRIPTIONAL REGULATION OF CHYMASE EXPRESSION IN MAST-CELLS - A CYTOKINE-DEPENDENT MECHANISM FOR CONTROLLING THE EXPRESSION OF GRANULE NEUTRAL PROTEASES OF HEMATOPOIETIC-CELLS

Although all mouse mast cells are derived from a common progenitor, th ese effector cells exhibit tissue-specific differences in their expres sion of the chymase family of serine proteases whose genes reside on c hromosome 14, Immature bone marrow-derived mast cells (mBMMC), develop ed in vitro with interleukin (IL) 3-enriched medium, were cultured in the presence or absence of IL-10 to determine at the molecular level h ow the expression of the individual chymases is differentially regulat ed, As assessed by RNA blot analysis, mBMMC contain high steady-state levels of the transcript that encodes mouse mast cell protease (mMCP) 5, but not the homologous chymase transcripts that encode mMCP-1, mMCP -2, or mMCP-4. Nevertheless, nuclear run-on analysis revealed that the se cells transcribe all four mast cell chymase genes. IL-10 elicited h igh steady-state levels of the mMCP-2 transcript, and pulse-chase expe riments revealed that the half-life of the mMCP-2 transcript in mBMMC maintained in the presence of IL-10 is similar to 4-fold longer than t hat in replicate cells subsequently cultured in medium without IL-10. Reverse transcription-polymerase chain reaction/ nucleotide sequence a nalysis demonstrated that mBMMC cultured in the absence or presence of IL-10 correctly process mMCP-2 pre-mRNA. Experiments with cycloheximi de and actinomycin D indicated that IL-10 induces expression of a tran s-acting factor(s) that stabilizes the mMCP-2 transcript or facilitate s its processing. The discovery that the expression of certain chymase s in mBMMC is regulated primarily at the post-transcriptional level pr ovides a basis for understanding the mechanism by which specific cytok ines dictate expression of the chromosome 14 family of serine protease s in cells that participate in inflammatory processes.