Microtubule-associated Protein 2c Reorganizes Both Microtubules and Microfilaments into Distinct Cytological Structures in an Actin-binding Protein-280–deficient Melanoma Cell Line

Abstract

The emergence of processes from cells often involves interactions between microtubules and microfilaments. Interactions between these two cytoskeletal systems are particularly apparent in neuronal growth cones. The juvenile isoform of the neuronal microtubule-associated protein 2 (MAP2c) is present in growth cones, where we hypothesize it mediates interactions between microfilaments and microtubules. To approach this problem in vivo, we used the human melanoma cell, M2, which lacks actin-binding protein-280 (ABP-280) and forms membrane blebs, which are not seen in wild-type or ABP-transfected cells. The microinjection of tau or mature MAP2 rescued the blebbing phenotype; MAP2c not only caused cessation of blebbing but also induced the formation of two distinct cellular structures. These were actin-rich lamellae, which often included membrane ruffles, and microtubule-bearing processes. The lamellae collapsed after treatment with cytochalasin D, and the processes retracted after treatment with colchicine. MAP2c was immunocytochemically visualized in zones of the cell that were devoid of tubulin, such as regions within the lamellae and in association with membrane ruffles. In vitro rheometry confirmed that MAP2c is an efficient actin gelation protein capable of organizing actin filaments into an isotropic array at very low concentrations; tau and mature MAP2 do not share this rheologic property. These results suggest that MAP2c engages in functionally specific interactions not only with microtubules but also with microfilaments.

HMWMAP2: New perspectives on a pathway to dendritic identity

“…MAP2 proteins also determine the spacing between microtubules [Chen et al, 1992;Cunningham et al, 1997;Belanger et al, 2002]. MAP2b and MAP2c induce a spacing between microtubules of 60 nm and 20 nm, respectively.…”

“…MAP2b and MAP2c induce a spacing between microtubules of 60 nm and 20 nm, respectively. Several studies indicated that the length of the projection domain was the main determinant of the spacing between microtubules [Chen et al, 1992;Cunningham et al, 1997;Belanger et al, 2002]. To further investigate this point, we generated truncated forms of MAP2b deleted from different portions of the projection domain and expressed them in Sf9 cells to measure their effects on microtubule spacing [Belanger et al, 2002].…”

Interaction of Microtubule-associated Protein-2 and p63

“…Thus, the stabilization of microtubules does not seem to be the sole function of MAP2 in dendritic outgrowth. In recent years, our work and that of others (23)(24)(25)(26)(27)(28)(29) showed that MAP2 could also interact with actin microfilaments and neurofilaments. Thus, MAP2 could act as a cytoskeletal integrator in dendrites by linking together the three cytoskeletal elements.…”

Regulated Association of Microtubule-associated Protein 2 (MAP2) with Src and Grb2: Evidence for MAP2 as a Scaffolding Protein

“…Besides microtubules, several additional proteins have been reported to interact with MAP2 in vitro, the best characterized of which is the type II regulatory subunit of PKA (32)(33)(34). Other proteins include F-actin (35)(36)(37)(38), calmodulin (39), and the mitochondrial outer membrane protein porin (40). The precise binding sites on MAP2 for these proteins have yet to be identified.…”