Interleukin 4 increases type 5 acid phosphatase mRNA expression in murine bone marrow macrophages

Type 5 acid phosphatase is a lysosomal enzyme expressed in cells of monocyte/macrophage lineage frequently used as a marker of osteoclastic differentiation. Oligonucleotide primers for DNA amplification were designed following sequence alignment of rat bone and human macrophage type 5 acid phosphatases. DNA (330 bp in length) obtained using these primers and reverse transcribed total cell RNA from in vitro generated murine osteoclastic cells was cloned and sequenced. DNA sequence analysis of two clones demonstrates that the amplified material was 91% and 96% identical to rat bone type 5 acid phosphatase at the nucleotide and amino acid level, respectively. Northern blots of murine tissue RNA show the presence of 1.5-kb transcripts that are most highly expressed in the long bones. Total cell RNA from the osteoclastic cells contain a marked level of type 5 acid phosphatase mRNA when compared to the levels seen in the tissue samples. Additionally, osteoclastic cell RNA contains two additional transcripts of 2.5 and 5 kb. Bone marrow macrophages grown in the presence of M-CSF express low levels of the 1.5-kb transcript with no signal observed for either of the two larger transcripts that were seen in the osteoclastic RNA samples. Importantly, bone marrow macrophage 1.5-kb type 5 acid phosphatase transcript levels are increased by interleukin 4 treatment in both a time and concentration-dependent manner. These findings indicate that type 5 acid phosphatase, while a cytochemical marker for osteoclasts, can be induced in macrophages by agents that block in vitro osteoclastic differentiation. Increased type 5 acid phosphatase may play a role in interleukin 4-stimulated monocyte activities.