Truncation of the Projection Domain of MAP4 (Microtubule-Associated Protein 4) Leads to Attenuation of Microtubule Dynamic Instability

Abstract

ABSTRACT. MAP4, a ubiquitous heat-stable MAP, is composed of an asymmetric structure common to the heatstable MAPs, consisting of an N-terminal projection (PJ) domain and a C-terminal microtubule (MT)-binding (MTB) domain. Although the MTB domain has been intensively studied, the role of the PJ domain, which protrudes from MT-wall and does not bind to MTs, remains unclear. We investigated the roles of the PJ domain on the dynamic instability of MTs by dark-field microscopy using various PJ domain deletion constructs of human MAP4 (PJ1, PJ2, Na-MTB and KDM-MTB). There was no obvious difference in the dynamic instability between the wtMAP4 and any fragments at 0.1 mM, the minimum concentration required to stabilize MTs. The individual MTs stochastically altered between polymerization and depolymerization phases with similar profiles of length change as had been observed in the presence of MAP2 or tau. We also examined the effects at the increased concentrations of 0.7 mM, and found that in some cases the dynamic instability was almost entirely attenuated. The length of both the polymerization and depolymerization phases decreased and "pause-phases" were occasionally observed, especially in the case of PJ1, PJ2 or Na-MTB. No obvious change was observed in the increased concentration of wtMAP4 and KDM-MTB. Additionally, the profiles of MT length change were quite different in 0.7 mM PJ2. Relatively rapid and long depolymerization phases were sometimes observed among quite slow length changes. Perhaps, this unusual profile could be due to the uneven distribution of PJ2 along the MT lattice. These results indicate that the PJ domain of MAP4 participates in the regulation of the dynamic instability.

Site-specific Microtubule-associated Protein 4 Dephosphorylation Causes Microtubule Network Densification in Pressure Overload Cardiac Hypertrophy

“…Indeed, fusion proteins consisting solely of the MAP4 projection domain do not bind to microtubules in vitro (44,45). What is known about the role of the projection domain in MAP4 interactions with microtubules is that, as might be expected, it affects the spacing and packing of the microtubule array (46), and its presence also appears to be important for normal microtubule dynamic instability (47). Further, evidence derived from an expression construct of the MAP4 projection domain indicates that, although it does not bind to microtubules, it does have a major effect on the activity of the MAP4 microtubulebinding domain; of special interest here, this has been thought to be mediated by phosphorylation of one or more potential sites in the MAP4 projection domain (44).…”

Transcriptional Modulation of Genes Encoding Structural Characteristics of Differentiating Enterocytes During Development of a Polarized Epithelium In Vitro

“…These included MAP4, which increases the rescue frequency of microtubules (Permana et al, 2005) and reduces vesicle motility and organelle movement (Bulinski et al, 1997), and was down-regulated over the time course. The expression of KIFC3, which has been implicated in Golgi positioning and apical transport (Noda et al, 2001;Xu et al, 2002) was increased.…”

MAP4 Mechanism that Stabilizes Mitochondrial Permeability Transition in Hypoxia: Microtubule Enhancement and DYNLT1 Interaction with VDAC1

“…A variety of MAPs have been identified in different cell types and they perform various functions, for example, the fine tuning of MT dynamics to stabilize and destabilize MTs when guiding MTs towards specific cellular locations, MT cross-linking, and mediating interactions between MTs and other proteins [16], [17], [18]. MAP4 is found in nearly all cell types and is responsible for stabilization of MTs [19]. Takahashi et al [20] reported that overexpression of MAP4 caused a shift of tubulin dimers to a polymerized fraction and formed dense, stable MT networks; overexpression also caused elevated tubulin expression and altered MT network properties [21].…”