Overexpression of full- or partial-length MAP4 stabilizes microtubules and alters cell growth.
To investigate the in vivo functions of MAP4, a microtubule-associated protein expressed almost ubiquitously in vertebrate cells, we prepared stably transfected clonal mouse Ltk- cell lines expressing full-length MAP4 (L-MAP4 cells) or its MT-binding domain (L-MTB cells). Although transfectants showed no dramatic defect in morphology, organellar distribution, or level of MT polymer, as compared to naive Ltk- cells or L-MOCK cells (transfected with vector alone), MTs in L-MAP4 and L-MTB cells showed greater stability than those in control cells, as monitored by the level of post-translationally detyrosinated alpha-tubulin and by a quantitative nocodazole-resistance assay. In vivo, the MT-binding domain of MAP4 stabilized MTs less potently than full-length MAP4, in contrast to the equivalent efficacy demonstrated in studies of in vitro MT polymerization (Aizawa et al. (1991), J. Biol. Chem. 266, 9841-9846), L-MAP4 and L-MTB cells grew significantly more slowly than control cells; this growth inhibition was not due to mitotic arrest or cell death. L-MAP4 and L-MTB cells also exhibited greater tolerance to the MT-depolymerizing agent, nocodazole, but not to the MT-polymerizing agent, Taxol. Our results demonstrate that MAP4 and its MT-binding domain are capable of MT stabilization in vivo, and that increasing the intracellular level of MAP4 affects cell growth parameters.
Nguyen
H L
HL
Department of Pathology, Columbia University, College of Physicians & Surgeons, New York, NY 10032, USA.
Chari
S
S
Gruber
D
D
Lue
C M
CM
Chapin
S J
SJ
Bulinski
J C
JC
D000818:Animals; D002455:Cell Division; D015870:Gene Expression; D006801:Humans; D007739:L Cells; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000502:physiology*; D008870:Microtubules / Q000502:physiology*; D015739:Nocodazole / Q000494:pharmacology; D014162:Transfection
D008869:Microtubule-Associated Proteins; D015739:Nocodazole