Targeting of a tropomyosin isoform to short microfilaments associated with the Golgi complex.
A growing body of evidence suggests that the Golgi complex contains an actin-based filament system. We have previously reported that one or more isoforms from the tropomyosin gene Tm5NM (also known as gamma-Tm), but not from either the alpha- or beta-Tm genes, are associated with Golgi-derived vesicles (Heimann et al., (1999). J. Biol. Chem. 274, 10743-10750). We now show that Tm5NM-2 is sorted specifically to the Golgi complex, whereas Tm5NM-1, which differs by a single alternatively spliced internal exon, is incorporated into stress fibers. Tm5NM-2 is localized to the Golgi complex consistently throughout the G1 phase of the cell cycle and it associates with Golgi membranes in a brefeldin A-sensitive and cytochalasin D-resistant manner. An actin antibody, which preferentially reacts with the ends of microfilaments, newly reveals a population of short actin filaments associated with the Golgi complex and particularly with Golgi-derived vesicles. Tm5NM-2 is also found on these short microfilaments. We conclude that an alternative splice choice can restrict the sorting of a tropomyosin isoform to short actin filaments associated with Golgi-derived vesicles. Our evidence points to a role for these Golgi-associated microfilaments in vesicle budding at the level of the Golgi complex.
Percival
Justin M
JM
Oncology Research Unit, The Children's Hospital at Westmead, Westmead, NSW 2145, Australia.
Hughes
Julie A I
JA
Brown
Darren L
DL
Schevzov
Galina
G
Heimann
Kirsten
K
Vrhovski
Bernadette
B
Bryce
Nicole
N
Stow
Jennifer L
JL
Gunning
Peter W
PW
D020823:ADP-Ribosylation Factor 1 / Q000378:metabolism*; D008841:Actin Cytoskeleton / Q000378:metabolism*; D000199:Actins / Q000378:metabolism; D017398:Alternative Splicing / Q000235:genetics; D000818:Animals; D020126:Brefeldin A / Q000494:pharmacology; D015638:Cytochalasin D / Q000494:pharmacology; D022162:Cytoplasmic Vesicles / Q000378:metabolism; D016193:G1 Phase; D006056:Golgi Apparatus / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D041681:NIH 3T3 Cells; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D021381:Protein Transport / Q000502:physiology; D022502:Stress Fibers / Q000378:metabolism*; D014335:Tropomyosin / Q000235:genetics / Q000378:metabolism*
D000199:Actins; D020033:Protein Isoforms; D011500:Protein Synthesis Inhibitors; C411923:Tpm3 protein, mouse; D014335:Tropomyosin; D020126:Brefeldin A; D015638:Cytochalasin D; D020823:ADP-Ribosylation Factor 1