Intracellular trafficking of LET-756, a fibroblast growth factor of C. elegans, is controlled by a balance of export and nuclear signals.
The superfamily of fibroblast growth factors (FGF), which counts 22 members in humans, exerts many functions during animal development and adult life. LET-756 is one of the two FGFs of the nematode C. elegans. Re-introduction of LET-756 in a null mutant strain restores viability, allowing the study of structural requirements for LET-756 trafficking and function. LET-756 protein has several regions and motifs, including a non-classical internal motif required for secretion. We show here that a main difference in the wild-type LET-756 molecule and a truncated molecule that mimics a partial loss-of-function mutant lies on subnuclear expression. Using Cos-1 cells and rescue activity we show that: (i) nuclear localization is due to various redundant NLS, one of them acting as a nucleolar localization signal; (ii) nuclear LET-756 is addressed to the speckles by a stretch of glutamine residues; (iii) nuclear LET-756 is trafficking between speckles and nucleoli; (iv) in the nucleolus, LET-756 is associated with proteins of the rRNA splicing compartment; (v) changing LET-756 secretion signal prevents its nuclear localization. We propose that LET-756 exerts its functions through a balance between secreted and nuclear forms due to two opposite addressing signals, (i) synergy of several NLS and (ii) attenuated secretion signal.
Popovici
Cornel
C
Institut de Cancérologie de Marseille, Laboratoire d'Oncologie Moléculaire, Institut Paoli-Calmettes et UMR599 INSERM, 27 Bd. Leï Roure, 13009 Marseille, France.
Fallet
Mathieu
M
Marguet
Didier
D
Birnbaum
Daniel
D
Roubin
Régine
R
D000818:Animals; D019556:COS Cells; D017173:Caenorhabditis elegans / Q000166:cytology / Q000235:genetics / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002466:Cell Nucleolus / Q000737:chemistry / Q000378:metabolism; D002522:Chlorocebus aethiops; D002868:Chromosomal Proteins, Non-Histone / Q000032:analysis; D003609:Dactinomycin / Q000494:pharmacology; D005346:Fibroblast Growth Factors / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D036681:Fluorescence Recovery After Photobleaching; D017353:Gene Deletion; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D042581:Intranuclear Space / Q000737:chemistry / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D019913:Nuclear Localization Signals / Q000235:genetics / Q000502:physiology*; D035463:Pol1 Transcription Initiation Complex Proteins / Q000032:analysis; D021381:Protein Transport / Q000187:drug effects; D017468:Receptors, Fibroblast Growth Factor / Q000235:genetics / Q000378:metabolism; D017412:Ribonucleoprotein, U1 Small Nuclear / Q000032:analysis; D014162:Transfection
D029742:Caenorhabditis elegans Proteins; D002868:Chromosomal Proteins, Non-Histone; C112493:EGL-15 protein, C elegans; C402375:Let-756 protein, C elegans; D019913:Nuclear Localization Signals; D035463:Pol1 Transcription Initiation Complex Proteins; D017468:Receptors, Fibroblast Growth Factor; D017412:Ribonucleoprotein, U1 Small Nuclear; C047458:fibrillarin; C063844:transcription factor UBF; D049452:Green Fluorescent Proteins; D003609:Dactinomycin; D005346:Fibroblast Growth Factors