Leukocyte Antigen-related Protein Tyrosine Phosphatase Negatively Regulates Hydrogen Peroxide-induced Vascular Smooth Muscle Cell Apoptosis

Reactive oxygen species (ROS) have been implicated in vascular smooth muscle cell (VSMC) apoptosis, a hallmark of advanced atherosclerotic lesions. Transient oxidation and inactivation of protein-tyrosine phosphatases play a critical role in cellular response to ROS production. However, the function of leukocyte antigen-related (LAR) protein-tyrosine phosphatase in ROS signaling is not known. To determine the expression of LAR in ROS-induced apoptosis, we investigated hydrogen peroxide-induced cell death and signaling in aortic VSMCs from wild-type and LAR(-/-) mice. Histone- associated DNA fragmentation and caspase-3/7 activity were significantly enhanced, mitochondrial membrane integrity was compromised, and cell viability was significantly decreased following H2O2 treatment in LAR(-/-) VSMCs compared with wild-type cells. Stronger and sustained increase in autophosphorylation and activity of Fyn, an Src family tyrosine kinase, was observed in LAR(-/-) cells compared with wild-type cells following H2O2 treatment. LAR binds to activated Fyn in H2O2-treated VSMCs, and recombinant LAR dephosphorylates phosphorylated-Fyn in vitro. In addition, LAR deficiency enhanced H2O2-induced phosphorylation of Janus kinase 2 (JAK2), signal transducer and activator of transcription 3 (STAT3), and p38 mitogen-activated protein kinase (MAPK). PP2, a Fyn-specific inhibitor, blocked JAK2, STAT3, and p38 MAPK activation and significantly attenuated apoptosis induced by H2O2. AG490, a JAK2-specific inhibitor, significantly attenuated H2O2-induced apoptosis, and blocked H2O2-induced activation of STAT3, but not p38 MAPK in both wild-type and LAR(-/-) VSMCs. Attenuation of Fyn expression by short hairpin RNA significantly decreased H2O2-induced downstream signaling and apoptosis in VSMCs. Together, these data indicate that LAR regulates Fyn/JAK2/STAT3 and Fyn/p38 MAPK pathways involved in ROS-induced apoptosis.