Bidirectional transcytosis determines the steady state distribution of the transferrin receptor at opposite plasma membrane domains of BeWo cells

Abstract

Abstract. Trophoblast-like BeWo cells form wellpolarized epithelial monolayers, when cultured on permeable supports. Contrary to other polarized cell systems, in which the transferrin receptor is found predominantly on the basolateral cell surface, BeWo cells express the transferrin receptor at both apical and basolateral cell surfaces (Cerneus, D.P., and A. van der Ende. 1991. J. Cell Biol. 114: 1149-1158. In the present study we have addressed the question whether BeWo cells use a different sorting mechanism to target transferrin receptors to the cell surface, by examining the biosynthetic and transcytotic pathways of the transferrin receptor in BeWo cells. Using trypsin and antibodies to detect transferrin receptors at the cell surface of filter-grown BeWo cells, we show that at least 80 % of newly synthesized transferrin receptor follows a direct pathway to the basolateral surface, demonstrating that the transferrin receptor is efficiently intracellularly sorted. After surface arrival, pulselabeled transferrin receptor equilibrates between apical and basolateral cell surfaces, due to ongoing transcytotic transport in both directions. The subsequent redistribution takes over 120 min and results in a steady state distribution with 1.5-2.0 times more transferrin receptors at the basolateral surface than at the apical surface. By monitoring the fate of surfacebound '25I-transferrin, internalized either from the apical or basolateral surface transcytosis of the transferrin receptor was studied. About 15 % of t25I-transferrin is transcytosed in the basolateral to apical direction, whereas 25 % is transcytosed in the opposite direction, indicated that the fraction of receptors involved in transcytosis is roughly twofold higher for the apical receptor pool, as compared to the basolateral pool. Upon internalization, both apical and basolateral receptor pools become redistributed on both surfaces, resulting in a twofold higher number of transferrin receptors at the basolateral surface. Our results indicate that in BeWo Cells bidirectional transcytosis is the main factor in surface distribution of transferrin receptors on apical and basolateral surfaces, which may represent a cell type-specific, post-endocytic, sorting mechanism.

Mouse hepatitis virus strain A59 is released from opposite sides of different epithelial cell types.

“…Cells from a confluent culture in an 80 cm# culture flask were obtained by trypsinization and were suspended in 20 ml culture medium of which 1 ml was added per filter. The tightness of the monolayer was checked routinely by adding medium to the upper chamber up to a higher level than in the lower chamber (Cerneus et al, 1993 ;Rossen et al, 1994).…”

Placental Alkaline Phosphatase Expression at the Apical and Basal Plasma Membrane in Term Villous Trophoblasts

“…For the transferrin receptor, it has been shown that 80% of newly synthesized receptor is initially inserted into the basolateral domain. The steady-state distribution is then achieved by different rates of transcytosis of apical and basolateral receptors (Cerneus et al 1993a). It remains to be demonstrated whether newly synthesized PLAP is initially sorted to the apical domain and subsequently transcytosed to the basolateral side, with less transcytosis taking place in the opposite direction in BeWo cells.…”

Cell-to-Cell Contact Results in a Selective Translocation of Maternal Human Immunodeficiency Virus Type 1 Quasispecies across a Trophoblastic Barrier by both Transcytosis and Infection

“…in a two-chamber system for 5 days. Under these conditions, BeWo cells form a tight, polarized monolayer that mimicked the trophoblastic barrier in vivo (12,13). We checked the integrity of target BeWo cell monolayers at the onset of the experiments and after contact with infectious material by using three parameters.…”