Molecular cloning and characterization of a novel cystatin-like molecule, CLM, from human bone marrow stromal cells

The cystatins are physiological cysteine proteinase inhibitors. Here we report the cloning of a novel human cystatin-like molecule (CLM) from human bone marrow stromal cell (BMSC) cDNA library. The putative CLM protein contained 159 residues with a 29-residue signal peptide. CLM protein was highly homologous to family 2 cystatins, especially mouse and human testatin. The CLM gene spanned two exons and was mapped on chromosome 20p11.2, among cystatin superfamily gene clusters. CLM mRNA was barely detected in most tumor cell lines except for breast adenocarcinoma MCF-7 cells and glioblastoma U251 cells, but after LPS or PMA stimulation, CLM expression was increased in myelogenous leukemia cell lines HL-60 and U-937. Northern blot analysis revealed CLM was ubiquitously expressed in normal tissues, which was clearly different from the testis-specific expression pattern of most family 2 cystatins. When overexpressed in 293 cells, GFP-fused CLM targeted extracellularly through secretory pathway by Golgi apparatus. The results indicated that the secreted CLM protein might play roles in hematopoietic differentiation or inflammation.