In addition to the PIN family proteins that are mainly involved in the intercellular Autin transport via the Auxin Polar Transport pathway (WP2941) mediated by PIN proteins located on the plasmamembrane, the Arabidopsis PIN family members PIN5, PIN6 and PIN8 are located on the endoplasmic reticulum membrane/envelope. PIN6 is also likely co-located with the nuclear membrane. According to Sawchuk MG et al. (2013) PIN5, PIN6 and PIN8 play roles in leaf vein patterning. PIN5 and PIN8 play an antagonistic role in regulating the intercellular auxin transport as well as in gametophyte (pollen) and sporophyte development.
Not much is known about the direction of auxin flow mediated by the PILS. However, they help in increasing the free auxin amount in the cytoplasm.