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.
Institut de Cancérologie de Marseille, Laboratoire d'Oncologie Moléculaire, Institut Paoli-Calmettes et UMR599 INSERM, 27 Bd. Leï Roure, 13009 Marseille, France.
Cornel
C
Popovici
Mathieu
M
Fallet
Didier
D
Marguet
Daniel
D
Birnbaum
Régine
R
Roubin
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