APICAL SORTING OF INFLUENZA HEMAGGLUTININ BY TRANSCYTOSIS IN RETINAL-PIGMENT EPITHELIUM

The retinal pigment epithelium is endowed with a unique distribution o f certain plasma membrane proteins, Na+,K+-ATPase, for instance, is po larized to the apical surface of RPE, rather than to the basolateral s urface as in most other epithelia. To study the sorting pathways of RP E cells, we used temperature sensitive mutants of influenza and vesicu lar stomatitis virus (VSV) to synchronize the transport of hemagglutin in (HA) and VSV G protein (VSV G) along the biosynthetic pathway of th e RPE cell line RPE-J, After HA and VSV G accumulated in the trans-Gol gi network of RPE-J cells kept at 20 degrees C, transfer to the permis sive temperature (32 degrees C) resulted in the transport of both HA a nd VSV G to the basolateral plasma membrane, Later, while VSV G remain ed basolateral, HA progressively reversed its polarity, eventually bec oming apical, Further analysis demonstrated that the reversal of HA po larity was due to transcytosis of HA from the basolateral to the apica l surface of RPE-J cells, To determine whether HA followed a transcyto tic route in RPE in vivo, influenza and VSV were injected into the sub retinal space of rat eyes, Again, both HA and VSV G were initially obs erved at the basolateral surface of RPE cells, However, whereas VSV G remained there, HA progressively redistributed to the apical surface, These findings demonstrated that RPE cells use a transcytotic pathway for the targeting of at least some apical proteins to their destinatio n.