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Journal of Cell Science 115, 1049-1058 (2002)
© 2002 The Company of Biologists Limited

Research Article

Cell-type-specific and selectively induced expression of members of the p24 family of putative cargo receptors

Jutta Rötter, Roland P. Kuiper, Gerrit Bouw and Gerard J. M. Martens*

Department of Molecular Animal Physiology, Nijmegen Center for Molecular Life Sciences (NCMLS), University of Nijmegen, Geert Grooteplein Zuid 28, 6525 GA Nijmegen, The Netherlands

* Author for correspondence (e-mail: gmartens{at}ncmls.kun.nl )

Accepted 28 November 2001

Members of the p24 family of type I transmembrane proteins are highly abundant in transport vesicles and are thought to be involved in selective protein transport between the endoplasmic reticulum and the Golgi complex. The p24 proteins have been grouped into four subfamilies ({alpha}, ß, {gamma}, and {delta}) and appear to assemble into tetrameric complexes that contain only one representative from each subfamily. Here we molecularly dissected the p24 family in a single cell type, namely in the intermediate pituitary melanotrope cells of the amphibian Xenopus laevis. The biosynthetic activity of these cells for production of their major cargo protein proopiomelanocortin (POMC) can be physiologically manipulated via the process of background adaptation (~30-fold induction, with highly active cells in black toads and virtually inactive cells in white animals). Extensive cDNA library screening revealed the identity of six p24 proteins expressed in the Xenopus melanotrope cells, namely one member of the p24{alpha} ({alpha}3), one of the p24ß (ß1), two of the p24{gamma} ({gamma}2, {gamma}3) and two of the p24{delta} ({delta}1, {delta}2) subfamily. Two other Xenopus p24 proteins, Xp24{alpha}2 and -{gamma}1, were not expressed in the melanotrope cells, pointing to cell-type specific p24 expression. Of the six melanotrope p24 proteins, the expression of four (Xp24{alpha}3, -ß1, -{gamma}3 and -{delta}2) was 20- to 30-fold induced in active versus inactive melanotropes, whereas that of the other two members (Xp24{gamma}2 and -{delta}1) had not or only slightly increased. The four proteins were induced only in the intermediate melanotrope cells and not in the anterior pituitary cells, and displayed similar overall tissue distributions that differed from those of Xp24{gamma}1, -{gamma}2 and -{delta}1. Together, our results reveal that p24 expression can be cell-type specific and selectively induced, and suggest that in Xenopus melanotrope cells an {alpha}3/ß1/{gamma}3/{delta}2 p24 complex is involved in POMC transport through the early stages of the secretory pathway.

Key words: p24 proteins, Protein transport, Prohormone-producing cell, Pituitary, Xenopus laevis




This article has been cited by other articles:


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G. Bouw, R. Van Huizen, E. J.R. Jansen, and G. J.M. Martens
A Cell-Specific Transgenic Approach in Xenopus Reveals the Importance of a Functional p24 System for a Secretory Cell
Mol. Biol. Cell, March 1, 2004; 15(3): 1244 - 1253.
[Abstract] [Full Text] [PDF]


© The Company of Biologists Ltd 2002