The cytoplasmic tail of FPC antagonizes the full-length protein in the regulation of mTOR pathway.
FPC (fibrocystin or polyductin) is a single transmembrane receptor-like protein, responsible for the human autosomal recessive polycystic kidney disease (ARPKD). It was recently proposed that FPC undergoes a Notch-like cleavage and subsequently the cleaved carboxy(C)-terminal fragment translocates to the nucleus. To study the functions of the isolated C-tail, we expressed the intracellular domain of human FPC (hICD) in renal epithelial cells. By 3-dimensional (3D) tubulogenesis assay, we found that in contrast to tubule-like structures formed from control cells, hICD-expressing cells exclusively formed cyst-like structures. By western blotting, we showed that the Akt/mTOR pathway, indicated by increased phosphorylation of Akt at serine 473 and S6 kinase 1 at threonine 389, was constitutively activated in hICD-expressing cells, similar to that in FPC knockdown cells and ARPKD kidneys. Moreover, application of mTOR inhibitor rapamycin reduced the size of the cyst-like structures formed by hICD-expressing cells. Application of either LY294002 or wortmannin inhibited the activation of both S6K1 and Akt. Expression of full-length FPC inhibited the activation of S6 and S6 kinase whereas co-expression of hICD with full-length FPC antagonized the inhibitory effect of full-length FPC on mTOR. Taken together, we propose that FPC modulates the PI3K/Akt/mTOR pathway and the cleaved C-tail regulates the function of the full-length protein.
Renal Division, Department of Medicine and Center of Polycystic Kidney Disease, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, United States of America.
Shixuan
S
Wang
Renal Division, Department of Medicine and Center of Polycystic Kidney Disease, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, United States of America.
Maoqing
M
Wu
Renal Division, Department of Medicine and Center of Polycystic Kidney Disease, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, United States of America.
Gang
G
Yao
Renal Division, Department of Medicine and Center of Polycystic Kidney Disease, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, United States of America.
Jingjing
J
Zhang
Renal Division, Department of Medicine and Center of Polycystic Kidney Disease, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, United States of America.
Jing
J
Zhou
D002478:Cells, Cultured; D002675:Child, Preschool; D004789:Enzyme Activation; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D017044:Polycystic Kidney, Autosomal Recessive / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D011956:Receptors, Cell Surface; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; C451750:PKHD1 protein, human