The receptor for PDGF, PDGFR is classified as a receptor tyrosine kinase (RTK), a type of cell surface receptor. Two types of PDGFRs have been identified: alpha type and beta type PDGFRs. The alpha type binds to PDGF-AA, PDGF-BB and PDGF-AB while the beta type PDGFR binds with high affinity to PDGF-BB and PDGF-AB. PDGF binds to PDGFRs ligand binding pocket located within the second and third immunoglobulin domains. Upon activation by PDGF, these receptors dimerise, and are "switched on" by auto-phosphorylation of several sites on their cytosolic domains, which serve to mediate binding of cofactors and subsequently activate signal transduction, for example, through the PI3K pathway. The role of PI3K has been investigated by several laboratories. Accumulating data suggests that while this molecule is generally part of growth signaling complex, it plays a more profound role in controlling cell migration.