Abstract
The microtubule-associated protein 4 (MAP4) has recently been shown to counteract destabilization of interphase microtubules caused by catastrophe promotion but not by tubulin sequestering. To address how MAP4 discriminates between destabilization of microtubules by these two mechanisms, we have evaluated the combined phenotypes of MAP4 coexpressed with Op18/stathmin family member derivatives with either catastrophe-promoting or sequestering activities. This approach relies on the finding that overexpression of MAP4 alone stabilizes microtubules during all phases of the cell cycle in human leukemia cells, and causes a potent mitotic block and a dramatic, previously unobserved, phenotype characterized by large monoastral spindles. Coexpression of either catastrophe-promoting or tubulin-sequestration-specific Op18 derivatives was found to modulate the activity of ectopic MAP4 during mitosis, but with differential functional outcome. Interestingly, the tubulin-sequestering derivative suppressed the monoastral mitotic phenotype of MAP4 (i.e. coexpression facilitated the formation of functional spindles). To evaluate whether this phenotypic suppression could be explained by tubulin-sequestration-dependent modulation of MAP4 activity, a plasma-membrane-targeted, tubulin-sequestering chimera was constructed to decrease the cytosolic free tubulin concentration substantially. This chimera likewise suppressed the monoastral phenotype caused by overexpression of MAP4, suggesting a direct downregulation of MAP4 activity by reduced free tubulin concentrations.
Highlights
Microtubules (MTs) are polar dynamic polymers that serve a multitude of cellular functions
The tubulin-sequestering derivative suppressed the monoastral mitotic phenotype of microtubule-associated protein 4 (MAP4)
To evaluate whether this phenotypic suppression could be explained by tubulin-sequestration-dependent modulation of MAP4 activity, a plasma-membranetargeted, tubulin-sequestering chimera was constructed to decrease the cytosolic free tubulin concentration substantially
Summary
Microtubules (MTs) are polar dynamic polymers that serve a multitude of cellular functions. MTs segregate chromosomes during mitosis, serve as tracks for cellular transport and regulate cell-type-specific shape and polarity during interphase (reviewed by Desai and Mitchison, 1997). These diverse functions require transitions between stable and dynamic forms of MTs, which are regulated by two main classes of MT regulators. The other class consists of two distinct types of MT-destabilizing protein, namely Op18/stathmin family members and members of the Kin I kinesin subfamily of kinesins such as XKCM1 (termed MCAK in humans) (reviewed by Walczak, 2000) Specific members of these families have been shown to promote transitions from growing to shrinking MTs (i.e. catastrophes) and are termed catastrophe promotors
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
