Abstract

The type 5, iron-containing, tartrate-resistant acid phosphatase (TR-AP) constitutes a relatively minor intracellular isozyme of acid phosphatase in the human that is immunologically related to uteroferrin, a secreted progesterone-induced protein of the porcine uterus. Here, the purification of small amounts of TR-AP from human placenta is described. When a placental lambda gt11 cDNA library was screened with two short 32P-labeled cDNA clones from within the coding region of uteroferrin, a 1412-base pair cDNA was identified that encodes the entire human TR-AP isozyme. This cDNA contains an open reading frame of 969 base pairs, corresponding to a protein of 323 amino acids. A putative signal sequence of 19 amino acids and two potential glycosylation sites are present. The deduced amino acid sequence of the human TR-AP is 85% identical to that of porcine uteroferrin (whose sequence is also reported here in complete form for the first time) and 82% identical to the corresponding regions of a partial amino acid sequence of a bovine spleen phosphoprotein phosphatase. Northern blotting techniques employing a labeled TR-AP cDNA probe revealed the presence of a 1.5-kilobase transcript in white cells from a patient with hairy cell leukemia, in human K562 erythroleukemic cells, and in Epstein-Barr virus-transformed human B-cells, but not in a human T-cell line. Culture of K562 cells in presence of 10(-8) M phorbol 12-myristate 13-acetate ester for 48-72 h enhanced TR-AP activity per cell about 30-fold and led to a corresponding increase in TR-AP mRNA levels.