ADAM28 is expressed by epithelial cells

ADAM28 (disintegrin and metalloproteinase 28), initially described as specific for lymphocytes, is overexpressed by cancer cells and plays a key role in cell proliferation and the progression of human lung and breast carcinomas. We studied the expression of ADAM28 in normal human tissues and examined its biological function. Using ADAM28-specific antibodies.

ADAM28 was immunolocalized primarily in epithelial cells of several tissues, including epididymis, bronchi, and stomach, while lymphocytes from lymph nodes and spleen were immunostained negligibly. RT-PCR, immunoblotting, and ELISA analyzes confirmed expression in these tissues, and low or negligible expression by lymphocytes was found in lymph nodes and spleen.

C1q was identified as a candidate ADAM28-binding protein from a human lung cDNA library by a yeast two-hybrid system, and specific binding was demonstrated by binding assays, immunoprecipitation and surface plasmon resonance. C1q treatment of normal BEAS-2B and NHBE bronchial epithelial cells, both of which showed low expression of ADAM28, caused apoptosis by activation of p38 and caspase-3, and cell death with autophagy by accumulation of LC3-II and autophagosomes, respectively.

C1q-induced cell death was attenuated by treatment of cells with antibodies against the C1q receptor gC1qR/p33 or cC1qR/calreticulin. Treatment of C1q with recombinant ADAM28 prior to addition to culture medium reduced C1q-induced cell death, and knockdown of ADAM28 using siRNA increased cell death. These data demonstrate that ADAM28 is expressed by epithelial cells of several normal organs and suggest that ADAM28 plays a role in cell survival by suppressing C1q-induced cytotoxicity in bronchial epithelial cells.

Members of the ADAM (disintegrin and metalloproteinase) gene family are multifunctional molecules and are involved in various biological and pathological events such as cell adhesion and migration, cell fusion, spermatogenesis, neurogenesis, angiogenesis, inflammatory cell infiltration and cancer cell proliferation. and evolution [1, 2].

They include 13 proteolytic ADAMs that have proteinase activity and eight non-proteolytic ADAMs [1, 3]. The typical structure of proteolytic ADAMs includes propeptide, metalloproteinase, disintegrin-like, cysteine-rich, epidermal growth factor-like, transmembrane, and cytoplasmic domains.