Abstract
Rab proteins are a family of small GTPases involved in a variety of cellular processes. The Rab11 subfamily in particular directs key steps of intracellular functions involving vesicle trafficking of the endosomal recycling pathway. This Rab subfamily works through a series of effector proteins including the Rab11-FIPs (Rab11 Family-Interacting Proteins). While the Rab11 subfamily has been well characterized at the cellular level, its function within human organ systems is still being explored. In an effort to further study these proteins, we conducted a preliminary investigation of a subgroup of endosomal Rab proteins in a range of human cell lines by Western blotting. The results from this analysis indicated that Rab11a, Rab11c(Rab25) and Rab14 were expressed in a wide range of cell lines, including the human placental trophoblastic BeWo cell line. These findings encouraged us to further analyse the localization of these Rabs and their common effector protein, the Rab Coupling Protein (RCP), by immunofluorescence microscopy and to extend this work to normal human placental tissue. The placenta is a highly active exchange interface, facilitating transfer between mother and fetus during pregnancy. As Rab11 proteins are closely involved in transcytosis we hypothesized that the placenta would be an interesting human tissue model system for Rab investigation. By immunofluorescence microscopy, Rab11a, Rab11c(Rab25), Rab14 as well as their common FIP effector RCP showed prominent expression in the placental cell lines. We also identified the expression of these proteins in human placental lysates by Western blot analysis. Further, via fluorescent immunohistochemistry, we noted abundant localization of these proteins within key functional areas of primary human placental tissues, namely the outer syncytial layer of placental villous tissue and the endothelia of fetal blood vessels. Overall these findings highlight the expression of the Rab11 family within the human placenta, with novel localization at the maternal-fetal interface.
Highlights
Rab proteins are a family of small molecular weight G-proteins that bind to a variety of downstream effectors in order to direct many key cellular functions
We initially examined by Western blot analysis the expression levels of Rab11 family members in cultured placental cell types as compared HeLa cervical cancer and H1299 lung cancer cell lines (S1 Fig, Fig 1)
We found that Rab11a and Rab11c were abundantly expressed in BeWo cells compared with these other cell types, while Rab11b was detected at much lower levels in all of the cell lines tested (Fig 1)
Summary
Rab proteins are a family of small molecular weight G-proteins that bind to a variety of downstream effectors in order to direct many key cellular functions. In their active state, Rabs have specific intracellular localizations and control specific biosynthetic and endocytic trafficking pathways, which define their function. Rab has been studied in a variety of model systems with many important implications for human health and disease [1] With their central role in vesicle trafficking, continued analysis of the Rab family within physiologic exchange interfaces can provide important insights into its function. We examined the expression and localization of Rab subfamily members and their effectors in the human placenta
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