IDENTIFICATION OF A NEW ACUTE-PHASE PROTEIN

We have previously reported mouse SIP24 protein as a secreted inducibl e protein produced by quiescent Balb/c 3T3 cells. SIP24 can be produce d in response to many factors, including serum, basic fibroblast growt h factor, prostaglandin F2 alpha, phorbol ester, and dexamethasone. He re we present evidence to show that SIP24 is the product of mouse 24P3 mRNA. The 24P3 cDNA was originally cloned from an SV40-transformed qu iescent mouse primary kidney cell culture, and it has been classified as a new member of the lipocalin protein family. We show that the SIP2 4/24P3 protein and mRNA increase dramatically in mouse serum and liver during the acute phase response induced by turpentine injection. Inje ction of mice with dexamethasone caused a modest increase of SIP24/24P 3 mRNA in the liver. Tissue distribution studies revealed that SIP24/2 4P3 is mainly expressed in liver during the acute phase response. SIP2 4/24P3 was also detected in the brain and the uterus. In mouse BNL (Ba lb/c normal liver) cells, the production of SIP24/24P3 is stimulated b y tumor necrosis factor alpha, which is a major regulator of the expre ssion of other acute phase proteins. From its pattern of regulation, w e conclude that SIP24/24P3 is a new type 1 acute phase protein.