Proteinase 3/myeloblastin as a growth factor in human kidney cells

Numerous data support the possible role of myeloblastin/proteinase 3 (PR3) in growth and differentiation of neutrophil granulocytes and certain monocyte subtypes. However, whether PR3 is expressed in non-myeloid cells remains a matter of debate even though recent studies clearly demonstrated its expression in endothelium, kidney epithelial cells and epithelial tumor cell lines.

To survey PR3 transcript presence in human tissues, we analyzed different human tissues by dot blot and northern blot using a cloned PR3-cDNA probe. To examine the physiological function of PR3 expression in non-myeloid cells, we constructed different recombinant retroviral vectors containing human PR3-cDNA variants and expressed them in tubular epithelial cells (TEC). Using an MTT-based proliferation assay, we determined the proliferation rate of PR3-transduced kidney cells.

The resulting expression pattern clearly indicated that PR3 transcripts are not only present in tissues known to harbor hematopoietic cells, but surprisingly PR3 was highly expressed in fetal organs including the kidney. The proliferation assay revealed that the growth rate of TEC transduced with native PR3 was significantly enhanced relative to non-transduced TEC.

The results supported our theory that PR3 can act as a growth factor in non-hematopoietic cells, analogous to its role in hematopoietic cells. The cells, recombinant vectors and methods described here serve as a basis to investigate PR3 function in cellular differentiation and proliferation, as well as its role in autoimmune diseases.