A potential role for α-actinin in inside-out αIIbβ3 signaling

• Published in: Blood 2011-01, Vol.117 (1), p.250-258
• Main Authors: Tadokoro, Seiji, Nakazawa, Tsuyoshi, Kamae, Tsuyoshi, Kiyomizu, Kazunobu, Kashiwagi, Hirokazu, Honda, Shigenori, Kanakura, Yuzuru, Tomiyama, Yoshiaki
• Format: Article
• Language: English
• Subjects: Actinin - genetics; Actinin - metabolism; Biological and medical sciences; Blood Platelets - metabolism; Blotting, Western; Flow Cytometry; Hematologic and hematopoietic diseases; Humans; Immunoprecipitation; Leukemia, Megakaryoblastic, Acute - genetics; Leukemia, Megakaryoblastic, Acute - metabolism; Leukemia, Megakaryoblastic, Acute - pathology; Medical sciences; Phosphorylation; Platelet Aggregation; Platelet Glycoprotein GPIIb-IIIa Complex - genetics; Platelet Glycoprotein GPIIb-IIIa Complex - metabolism; Receptor, PAR-1 - genetics; Receptor, PAR-1 - metabolism; Receptor, PAR-2 - genetics; Receptor, PAR-2 - metabolism; Receptors, Purinergic P2Y12 - deficiency; Receptors, Purinergic P2Y12 - genetics; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - genetics; Thrombasthenia - genetics; Thrombasthenia - metabolism; Thrombasthenia - pathology; Tumor Cells, Cultured; Tyrosine - metabolism
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2009-10-246751

Many different biochemical signaling pathways regulate integrin activation through the integrin cytoplasmic tail. Here, we describe a new role for α-actinin in inside-out integrin activation. In resting human platelets, α-actinin was associated with αIIbβ3, whereas inside-out signaling (αIIbβ3 activation signals) from protease-activated receptors (PARs) dephosphorylated and dissociated α-actinin from αIIbβ3. We evaluated the time-dependent changes of the αIIbβ3 activation state by measuring PAC-1 binding velocity. The initial velocity analysis clearly showed that PAR1-activating peptide stimulation induced only transient αIIbβ3 activation, whereas PAR4-activating peptide induced long-lasting αIIbβ3 activation. When αIIbβ3 activation signaling dwindled, α-actinin became rephosphorylated and reassociated with αIIbβ3. Compared with control platelets, the dissociation of α-actinin from αIIbβ3 was only transient in PAR4-stimulated P2Y12-deficient platelets in which the sustained αIIbβ3 activation was markedly impaired. Overexpression of wild-type α-actinin, but not the mutant Y12F α-actinin, increased its binding to αIIbβ3 and inhibited PAR1-induced initial αIIbβ3 activation in the human megakaryoblastic cell line, CMK. In contrast, knockdown of α-actinin augmented PAR-induced αIIbβ3 activation in CMK. These observations suggest that α-actinin might play a potential role in setting integrins to a default low-affinity ligand-binding state in resting platelets and regulating αIIbβ3 activation by inside-out signaling.