Microtubule actin crosslinking factor 1b: a novel plakin that localizes to the Golgi complex

Abstract

MACF1 (microtubule actin crosslinking factor), also called ACF7 (actin crosslinking family 7) is a cytoskeletal linker protein that can associate with both actin filaments and microtubules. We have identified a novel alternatively spliced isoform of MACF1. We named this isoform MACF1b and renamed the original isoform MACF1a. MACF1b is identical to MACF1a, except that it has a region containing plakin (or plectin) repeats in the middle of the molecule. MACF1b is ubiquitously expressed in adult tissues with especially high levels in the lung. We studied the subcellular localization of MACF1b proteins in mammalian cell lines. In two lung cell lines, MACF1b was chiefly localized to the Golgi complex. Upon treatments that disrupt the Golgi complex, MACF1b redistributed into the cytosol, but remained co-localized with the dispersed Golgi ministacks. MACF1b proteins can be detected in the enriched Golgi fraction by western blotting. The domain of MACF1b that targets it to the Golgi was found at the N-terminal part of the region that contains the plakin repeats. Reducing the level of MACF1 proteins by small-interfering RNA resulted in the dispersal of the Golgi complex.

Plakins in striated muscle

“…ACF7/MACF1b is expressed in heart tissue and has been shown to localize to the Golgi complex in two human lung cell lines maintained in culture. 81 In the same study, subcellular fractionation experiments revealed that ACF7/MACF1b was detected principally in the Golgi-enriched fraction but not the endoplasmic reticulum (ER) fraction. Furthermore, ACF7/MACF1b was detected in the cytosol of cells treated with brefeldin A, a Golgi destabilizing agent, resulting in the displacement of the Golgi from the perinuclear region to the cytosol.…”

The role of microtubule actin cross-linking factor 1 (MACF1) in the Wnt signaling pathway

“…We performed whole-mount immunohistochemistry with anti-MACF1 CU119 antibody (Lin et al 2005) on wild-type and mutant embryos. MACF1 was ubiquitously expressed at E7.5, with the highest levels in the head fold and in the primitive streak of the wild-type embryo (Fig.…”

“…The primary antibodies used include anti-MACF1 (CU119), which recognizes all isoforms of MACF1 (Lin et al 2005), anti-T (brachyury), anti-OTX2 (Santa Cruz Biotechnology), and anti-phospho-Histone H3 (Upstate Biotechnology) antibodies. Phosphorylation of Histone H3 is correlated with chromosome condensation during cell division and used as a marker of cell proliferation.…”

“…The alternatively spliced isoforms, MACF1b and BPAG1b, contain variable numbers of plakin (or plectin) repeats between the plakin domain and spectrin repeats. MACF1b is involved in maintaining the structure of the Golgi complex (Lin et al 2005). In epithelial cells, another alternatively spliced isoform of BPAG1 (BPAG1e) forms a link between hemidesmosomes and keratin intermediate filaments.…”

Golgi-associated GSK3β regulates the sorting process of post-Golgi membrane trafficking

“…We suppose that the interaction between p230 and GSK3 is indirect and that additional TGNassociating protein(s) might be involved in the interaction. One of the most plausible candidates is microtubule-actin crosslinking factor 1 (MACF1) because MACF1 has been shown to interact with GSK3 and p230, localizes to the TGN, and is known to regulate the localization of CLASP2 to the plasma membrane (Chen et al, 2006;Kakinuma et al, 2004;Lin et al, 2005;Drabeck et al, 2006). On the other hand, CLASP2 has been shown to interact with another TGN golgin, GCC185 (Efimov et al, 2007).…”