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Functional diversity among p24 subfamily members
Author(s) -
Strating Jeroen R.P.M.,
Hafmans Theo G.M.,
Martens Gerard J.M.
Publication year - 2009
Publication title -
biology of the cell
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.543
H-Index - 85
eISSN - 1768-322X
pISSN - 0248-4900
DOI - 10.1042/bc20080075
Subject(s) - biology , xenopus , golgi apparatus , endoplasmic reticulum , secretory pathway , subfamily , microbiology and biotechnology , transgene , glycosylation , secretory protein , endogeny , glycoprotein , downregulation and upregulation , cleavage (geology) , gene , biochemistry , paleontology , fracture (geology)
Background information . The p24 protein family plays an important but unclear role at the ER (endoplasmic reticulum)–Golgi interface. A p24 member from each subfamily (p24α 3 , β 1 , γ 3 and δ 2 ) is upregulated with the prohormone POMC (pro‐opiomelanocortin) when Xenopus laevis intermediate pituitary melanotrope cells are physiologically activated. Here we explored the role of p24 by generating and analysing Xenopus with melanotrope cell‐specific transgene expression of p24β 1 or p24γ 3 , two of the p24 proteins coexpressed with POMC, and compared the results with those previously reported for the two other coexpressed p24s (p24α 3 and p24δ 2 ). Results . The transgene expression of p24β 1 or p24γ 3 did not affect the endogenous p24 proteins or affected only endogenous p24γ 3 respectively, whereas in transgenics expressing p24α 3 and p24δ 2 , the levels of all endogenous p24 proteins were strongly decreased. Nevertheless, as for p24α 3 but albeit to a lesser extent, in the p24β 1 ‐transgenic melanotrope cells the rate of cargo cleavage was reduced, probably reflecting reduced cargo transport from the ER, and POMC glycosylation and sulfation in the Golgi were not affected. The p24γ 3 ‐transgenic cells displayed features of both the p24α 3 ‐transgenics (reduced cargo cleavage, normal POMC sulfation) and the p24δ 2 ‐transgenics (affected POMC glycosylation). Conclusions . Our results show that the four upregulated proteins p24α 3 , β 1 , γ 3 and δ 2 have non‐redundant roles in the early secretory pathway, and suggest that each p24 subfamily member provides a proper ER/Golgi subcompartmental microenvironment, together allowing correct secretory protein transport and processing.