Open AccessLipid droplet and milk lipid globule membrane associated placental protein 17b (PP17b) is involved in apoptotic and differentiation processes of human epithelial cervical carcinoma cells
Author(s) -
Than Nandor G.,
Sumegi Balazs,
Bellyei Szabolcs,
Berki Timea,
Szekeres Gyorgy,
Janaky Tamas,
Szigeti Andras,
Bohn Hans,
Than Gabor N.
Publication year - 2003
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1033.2003.03475.x
Subject(s) - lipid droplet , protein kinase c , protein kinase a , lipid raft , microbiology and biotechnology , biology , phorbol , apoptosis , kinase , chemistry , biochemistry , signal transduction
The intracellular role of placental protein 17b (PP17b)/TIP47 has been controversial, because it is considered to be a protein required for mannose 6‐phosphate receptor transport from endosome to trans ‐Golgi as well as a neutral lipid droplet‐associated protein. The similarity between the amino acid sequences of PP17 variants, adipophilin and perilipins, and between their gene structures indicate that PP17b as well as other alternatively spliced PP17 variants belong to the lipid storage droplet protein family, containing also some differentiation factors. Using a specific antibody, PP17b was detected in lipid droplet fractions and co‐localized with neutral lipid droplets stained by Nile red, and fluorescently labelled PP17 antibody in HeLa cells with confocal microscopy. PP17b was also detected in milk, associated to milk lipid globule membranes. Cytostatic agents induced apoptosis and PP17b synthesis in HeLa cells, which was significantly inhibited by protein kinase C (PKC) inhibitor, indicating the involvement of NF‐κB and AP‐1 transcription factors in this process, while protein kinase A (PKA) inhibitor had only a modest inhibitory effect. Cell differentiation induced by dibutyryl cyclic AMP or phorbol myristate acetate also increased PP17b synthesis, demonstrating its strong involvement in cell differentiation. PP17b synthesis was higher in M than in G 0 /G 1 phases in control, apoptotic and differentiated cells. This data shows that PP17b is a neutral lipid droplet‐associated protein, and its expression is regulated by PKC‐ and PKA‐dependent pathways.