Two human tumor cell lines were analyzed for the production of human antileucoprotease (ALP). One of them, a human squamous lung carcinoma cell line (HS‐24) synthesized, as confirmed by Western blot analysis, high amounts of ALP in serum‐free medium. The supernatant inhibited elastase, chymotrypsin and trypsin. Northern blot analysis with an 18‐mer radiolabelled oligonucleotide, derived from an ALP specific cDNA clone, revealed a specific mRNA of about 700–800 nucleotides in HS‐24 tumor cells. In contrast, a secondary human lung tumor cell line (SB‐3), derived from the adrenal cortex, did not synthesize ALP when assayed under identical conditions. The supernatant inhibited only trypsin and chymotrypsin.
A calcium-binding protein was isolated from serum-free culture medium of human squamous carcinoma cells (HS 24). N-Terminal sequencing of the protein yielded 30 amino acids which were identical to the N-terminus of cystic fibrosis antigen. Northern blot analysis with an oligonucleotide derived from the N-terminus resulted in the detection of a transcript of approximately 600 bases. Screening of a HS 24-cDNA library with the same oligonucleotide led to the isolation of a 381-bp-cDNA encoding a protein of 93 amino acids. The corresponding protein has been identified as the calcium-binding protein MRP-8 usually found in Macrophages.
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