Protein-tyrosine phosphatases in the vessel wall: differential expression after acute arterial injury.

Many protein-tyrosine phosphatases (PTPases) have now been identified, but little is known about PTPase expression and regulation in vascular tissue and in vascular disease. Polymerase chain reaction (PCR) amplification and cDNA fingerprinting of PTPase catalytic domains, combined with random sequencing of PCR product libraries, identified 18 (8 receptor-like and 10 cytosolic) PTPases in the rat carotid artery and revealed differential expression of 5 of these PTPases during neointima formation after balloon catheter injury. In situ hybridization was used to localize mRNA expression in vessel cross sections for the 5 differentially expressed PTPases. This revealed that for 3 PTPases (SHP1, CD45, and PTPbeta), differential transcript abundance was due to appearance/loss of the cell types by which they were expressed (leukocytes for SHP1 and CD45, endothelial cells for PTPbeta). However, mRNA expression of 2 PTPases (PTPL1 and PTP1B) was specifically upregulated by proliferating and migrating smooth muscle cells (SMCs) in characteristic temporal and regional patterns in response to vessel damage. Quantitative PCR analysis showed that PTP1B and PTPL1 were induced approximately 30-fold and approximately 60-fold, respectively, by 2 weeks after injury in the damaged vessels compared with the uninjured vessels. PTP1B was rapidly upregulated in the media after vessel injury and remained highly expressed in the developing neointima. By contrast, PTPL1 expression did not increase dramatically until the SMCs had migrated into the intima. The differential expression of PTP1B and PTPL1 by SMCs after injury suggests roles for these PTPases in the regulation of vessel wall remodeling.

Proliferating and migrating mesangial cells responding to injury express a novel receptor protein-tyrosine phosphatase in experimental mesangial proliferative glomerulonephritis.

The mesangial cell provides structural support to the kidney glomerulus. A polymerase chain reaction-based cDNA display approach identified a novel protein-tyrosine phosphatase, rPTP-GMC1, whose transcript expression is transiently and dramatically up-regulated during the period of mesangial cell migration and proliferation that follows mesangial cell injury in the anti-Thy 1 model of mesangial proliferative glomerulonephritis in the rat. In situ hybridization analysis confirmed that rPTP-GMC1 mRNA is up-regulated specifically by mesangial cells responding to the injury and is not detectable in other cells in the kidney or in many normal tissues. In cell culture, rPTP-GMC1 is expressed by mesangial cells but not by glomerular endothelial or epithelial cells (podocytes). The longest transcript (7.5 kilobases) encodes a receptor-like protein-tyrosine phosphatase consisting of a single catalytic domain, a transmembrane segment, and 18 fibronectin type III-like repeats in the extracellular segment. A splice variant predicts a truncated molecule missing the catalytic domain. rPTP-GMC1 maps to human chromosome 12q15 and to the distal end of mouse chromosome 10. The predicted structure of rPTP-GMC1 and its pattern of expression in vivo and in culture suggest that it plays a role in regulating the adhesion and migration of mesangial cells in response to injury.