Rab27a GTPase modulates L-type Ca2 + channel function via interaction with the II–III linker of CaV1.3 subunit

• Rab27a and CaV1.3 co-localize at the basolateral membrane of the RPE.
• Rab27a interacts directly with CaV1.3 subunits via a MyRIP-homologous sequence.
• Rab27a interaction decreases CaV1.3 pore activity and alters voltage-dependence.
• Rab27a over-expression in ARPE-19 reduces both CaV1.3 activity and VEGF-A secretion.
• First evidence for direct modulation of ion channel activity by Rab27a

In a variety of cells, secretory processes require the activation of both Rab27a and L-type channels of the CaV1.3 subtype. In the retinal pigment epithelium (RPE), Rab27a and CaV1.3 channels regulate growth-factor secretion towards its basolateral side. Analysis of murine retina sections revealed a co-localization of both Rab27a and CaV1.3 at the basolateral membrane of the RPE. Heterologously expressed CaV1.3/β3/α2δ1 channels showed negatively shifted voltage-dependence and decreased current density of about 70% when co-expressed with Rab27a. However, co-localization analysis using α5β1 integrin as a membrane marker revealed that Rab27a co-expression reduced the surface expression of CaV1.3 only about 10%. Physical binding of heterologously expressed Rab27a with CaV1.3 channels was shown by co-localization in immunocytochemistry as well as co-immunoprecipitation which was abolished after deletion of a MyRIP-homologous amino acid sequence at the II–III linker of the CaV1.3 subunit. Rab27a over-expression in ARPE-19 cells positively shifted the voltage dependence, decreased current density of endogenous CaV1.3 channels and reduced VEGF-A secretion. We show the first evidence of a direct functional modulation of an ion channel by Rab27a suggesting a new mechanism of Rab and ion channel interaction in the control of VEGF-A secretion in the RPE.