Elsevier

Experimental Cell Research

Volume 239, Issue 2, 15 March 1998, Pages 243-253
Experimental Cell Research

Regular Article
The Interaction of Mip-90 with Microtubules and Actin Filaments in Human Fibroblasts

https://doi.org/10.1006/excr.1997.3875Get rights and content

Abstract

The novel microtubule-interacting protein Mip-90 was originally isolated from HeLa cells by using affinity columns of agarose derivatized with peptides from the C-terminal regulatory domain on β-tubulin. Biochemical and immunocytochemical data have suggested that the association of Mip-90 with the microtubule system contributes to its cellular organization. Here we report the interaction patterns of Mip-90 with microtubules and actin filaments in interphase human fibroblasts. A polyclonal monospecific antibody against Mip-90 was used for immunofluorescence microscopy analysis to compare the distribution patterns of this protein with tubulin and actin. A detailed observation of fibroblasts revealed the colocalization of Mip-90 with microtubules and actin filaments. These studies were complemented with experiments using cytoskeleton-disrupting drugs which showed that colocalization patterns of Mip-90 with microtubules and actin filaments requires the integrity of these cytoskeletal components. Interestingly, a colocalization of Mip-90 with actin at the leading edge of fibroblasts grown under subconfluency was observed, suggesting that Mip-90 could play a role in actin organization, particularly at this cellular domain. Mip-90 interaction with actin polymers was further supportedin vitroby cosedimentation and immunoprecipitation experiments. The cosedimentation analysis indicated that Mip-90 bound to actin filaments with an association constantKa= 1 × 106M−1, while an stoichiometry Mip-90/actin of 1:12 mol/mol was calculated. Western blots of the immunoprecipitates revealed that Mip-90 associated to both actin and tubulin in fibroblasts extracts. These studies indicate that Mip-90, described as a microtubule-interacting protein, also bears the capacity to interact with the microfilament network, suggesting that it may play a role in modulating the interactions between these cytoskeletal filaments in nonneuronal cells.

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