Identification of a New Acute Phase Protein

Abstract

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