 As a receptor, after holo-RBP is bound, STRA6 activates the JAK/STAT pathway, resulting in the activation of transcription factor, STAT5.These two functions—retinol transporter and cytokine receptor—while using different pathways, are processes that depend on each other.In the first step, holo-retinol binding protein (holo-RBP; simply means RBP bound to retinol, i.e.