The extremely conserved C-terminal region of Reelin is not necessary for secretion but is required for efficient activation of downstream signaling.
Reelin is a very large secreted glycoprotein essential for correct development of the mammalian brain. It is also implicated in higher functions and diseases of human brain. However, whether or not secretion of Reelin is regulated and how Reelin transmits signals remain largely unknown. Reelin protein is composed of an N-terminal F-spondin-like domain, Reelin repeats, and a short and highly basic C-terminal region (CTR). The primary sequence of CTR is almost completely conserved among vertebrates except fishes, indicating its importance. A prevailing idea regarding the function of CTR is that it is required for the secretion of Reelin, although this remains unproven. Here we aimed to clarify the function of Reelin CTR. Neither deleting most of CTR nor replacing CTR with unrelated amino acids affected secretion efficiency, indicating that CTR is not absolutely required for the secretion of Reelin. We also found that Reelin mutants without CTR were less potent in activating the downstream signaling in cortical neurons. Although these mutants were able to bind to the Reelin receptor ectodomain as efficiently as wild-type Reelin, quite interestingly, their ability to bind to the isolated cell membrane bearing Reelin receptors or receptor-expressing cells (including cortical neurons) was much weaker than that of wild-type Reelin. Therefore, it is concluded that the CTR of Reelin is not essential for its secretion but is required for efficient activation of downstream signaling events, presumably via binding to an unidentified "co-receptor" molecule(s) on the cell membrane.
Nakano
Yoshimi
Y
Department of Biomedical Science, Graduate School of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe-dori, Mizuho-ku, Nagoya, Aichi 467-8603, Japan.
Kohno
Takao
T
Hibi
Terumasa
T
Kohno
Shiori
S
Baba
Atsushi
A
Mikoshiba
Katsuhiko
K
Nakajima
Kazunori
K
Hattori
Mitsuharu
M
D019943:Amino Acid Substitution; D000818:Animals; D001927:Brain Diseases / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D019556:COS Cells; D015816:Cell Adhesion Molecules, Neuronal / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism* / Q000473:pathology; D002525:Cerebellar Cortex / Q000378:metabolism* / Q000473:pathology; D002522:Chlorocebus aethiops; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D041681:NIH 3T3 Cells; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism* / Q000473:pathology; D011485:Protein Binding / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D011956:Receptors, Cell Surface / Q000378:metabolism*; D000091042:Reelin Protein; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics
D015816:Cell Adhesion Molecules, Neuronal; D016326:Extracellular Matrix Proteins; D009419:Nerve Tissue Proteins; D011956:Receptors, Cell Surface; D000091042:Reelin Protein; C469363:reelin receptor; C000717127:RELN protein, human; C000717128:Reln protein, mouse; D012697:Serine Endopeptidases