Nuclear localization of p85s6k: functional requirement for entry into S phase.
Immunolocalization of a newly described isoform of p70s6k, termed p85s6k, demonstrated a predominantly nuclear location in rat embryo fibroblasts (REF-52), a compartment in which growth factor-mediated phosphorylation of S6 has recently been reported. Microinjection of expression vectors encoding either p85s6k or a fusion protein containing only the putative nuclear localization motifs led to the exclusive accumulation of both products in the nucleus. Consistent with such a localization, microinjection of affinity-purified anti-p85s6k IgG into the nucleus, but not the cytoplasm, blocked serum-induced initiation of DNA synthesis. Co-injection into the nucleus of the anti-p85s6k IgG with activated p70s6k, which lacks the antigenic epitope, rescued the S phase block, arguing that the antibody exerts its effects through inhibiting p85s6k function. The results indicate a novel role for S6 phosphorylation in the nucleus distinct from that in the cytoplasm, a role essential for mitogenesis.
Reinhard
C
C
Friedrich Miescher Institute, Basel, Switzerland.
Fernandez
A
A
Lamb
N J
NJ
Thomas
G
G
D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002451:Cell Compartmentation; D002467:Cell Nucleus / Q000201:enzymology*; D005347:Fibroblasts / Q000166:cytology; D005455:Fluorescent Antibody Technique; D007527:Isoenzymes / Q000276:immunology / Q000502:physiology*; D008845:Microinjections; D008969:Molecular Sequence Data; D017346:Protein Serine-Threonine Kinases / Q000276:immunology / Q000502:physiology*; D051381:Rats; D011994:Recombinant Proteins; D019893:Ribosomal Protein S6 Kinases; D016196:S Phase / Q000187:drug effects / Q000502:physiology*
D000906:Antibodies; D007527:Isoenzymes; D011994:Recombinant Proteins; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases