CD99-Derived Agonist Ligands Inhibit Fibronectin-Induced Activation of β1 Integrin through the Protein Kinase A/SHP2/Extracellular Signal-Regulated Kinase/PTPN12/Focal Adhesion Kinase Signaling Pathway

Abstract

The human CD99 protein is a 32-kDa glycosylated transmembrane protein that regulates various cellular responses, including cell adhesion and leukocyte extravasation. We previously reported that CD99 activation suppresses ␤1 integrin activity through dephosphorylation of focal adhesion kinase (FAK) at Y397. We explored a molecular mechanism underlying the suppression of ␤1 integrin activity by CD99 agonists and its relevance to tumor growth in vivo. CD99-Fc fusion proteins or a series of CD99-derived peptides suppressed ␤1 integrin activity by specifically interacting with three conserved motifs of the CD99 extracellular domain. CD99CRIII3, a representative CD99-derived 3-mer peptide, facilitated protein kinase A-SHP2 interaction and subsequent activation of the HRAS/RAF1/MEK/ERK signaling pathway. Subsequently, CD99CRIII3 induced FAK phosphorylation at S910, which led to the recruitment of PTPN12 and PIN1 to FAK, followed by FAK dephosphorylation at Y397. Taken together, these results indicate that CD99-derived agonist ligands inhibit fibronectin-mediated ␤1 integrin activation through the SHP2/ERK/PTPN12/FAK signaling pathway.

Prolyl isomerase Pin1: a promoter of cancer and a target for therapy

“…Moreover, PTP-PEST and FAK are two pivotal effectors of the RAS signal, which are involved in tumor metastasis 103 . Pin1 facilitates the interaction of PTP-PEST with FAK to accelerate the Tyr397 dephosphorylation of FAK, which consequently induce the metastasis of numerous cancers 104 , 105 .…”

CD99–PTPN12 Axis Suppresses Actin Cytoskeleton-Mediated Dimerization of Epidermal Growth Factor Receptor

“…To determine whether CD99 activation can disrupt EGF-induced dimerization and activation of EGFR, two breast cancer cell lines, MDA-MB-231 and MCF-7, were treated with CD99 agonist ligands, CD99CRIII3 or CD99-Fc. We previously demonstrated that CD99CRIII3, a CD99-derived peptide, can function as a CD99 agonist as efficiently as CD99 protein derivatives or anti-CD99 agonist monoclonal antibody [ 24 ]. Western blotting and in situ PLA showed that those two CD99 agonists significantly inhibited EGFR dimerization and phosphorylation at Y1068, which were induced by EGF ( Figure 4 A and Figure S4A ).…”

“…This observation is consistent with a previous study, which demonstrated that PTPN12 controls EphA3 activation by regulating actin cytoskeletal organization during Eph clustering [ 8 ]. Furthermore, we previously reported the molecular mechanism by which CD99 induces β1 integrin inactivation via PTPN12 activation [ 24 ]. Likewise, CD99CRIII3 showed significant inhibitory effects on EGF-induced EGFR dimerization and internalization via activation of PTPN12.…”

“…Western blotting and immunoprecipitation were carried out as described previously [ 24 ]. Serum-starved breast carcinoma cells were treated with the appropriate reagents for 15 min at 37 °C, 5% CO 2 .…”

“…It has been known that CD99 is implicated in various cellular processes including differentiation, apoptosis, homotypic aggregation, and proliferation of lymphocytes, extravasation of leukocytes, transport of several transmembrane proteins, and apoptosis of tumor cells [ 21 , 22 , 23 ]. We previously reported that CD99CRIII3, a CD99 agonistic peptide ligand, activated PKA-SHP2-HRAS-ERK1/2 signal transduction pathway, which led to upregulation of PTPN12 expression and interaction with its downstream targets, FAK and PIN1, resulting in dephosphorylation of FAK at Y397 [ 24 ]. Consistent with our study, CD99 regulates contact strength and motility of osteosarcoma cells through inhibition of the expression of coiled-coil containing protein kinase 2 (ROCK2), which is a crucial mediator of actin cytoskeleton remodeling [ 25 ].…”