Cytoskeletal organization in tropomyosin-mediated reversion of ras-transformation: Evidence for Rho kinase pathway.
Tropomyosin (TM) family of cytoskeletal proteins is implicated in stabilizing actin microfilaments. Many TM isoforms, including tropomyosin-1 (TM1), are down-regulated in transformed cells. Previously we demonstrated that TM1 is a suppressor of the malignant transformation, and that TM1 reorganizes microfilaments in the transformed cells. To investigate how TM1 induces microfilament organization in transformed cells, we utilized ras-transformed NIH3T3 (DT) cells, and those transduced to express TM1, and/or TM2. Enhanced expression of TM1 alone, but not TM2, results in re-emergence of microfilaments; TM1, together with TM2 remarkably improves microfilament architecture. TM1 induced cytoskeletal reorganization involves an enhanced expression of caldesmon, but not vinculin, alpha-actinin, or gelsolin. In addition, TM1-induced cytoskeletal reorganization and the revertant phenotype appears to involve re-activation of RhoA controlled pathways in DT cells. RhoA expression, which is suppressed in DT cells, is significantly increased in TM1-expressing cells, without detectable changes in the expression of Rac or Cdc42. Furthermore, expression of a dominant negative Rho kinase, or treatment with Y-27632 disassembled microfilaments in normal NIH3T3 and in TM1 expressing cells. These data suggest that reactivation of Rho kinase directed pathways are critical for TM1-mediated microfilament assemblies.
Shah
V
V
Wistar Institute of Anatomy and Cell Biology, Philadelphia, Pennsylvania, USA.
Bharadwaj
S
S
Kaibuchi
K
K
Prasad
G L
GL
D016475:3T3 Cells; D008841:Actin Cytoskeleton / Q000378:metabolism; D000818:Animals; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000096:biosynthesis / Q000235:genetics; D003599:Cytoskeleton / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015536:Down-Regulation; D029721:Drosophila Proteins; D005786:Gene Expression Regulation; D011905:Genes, ras; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D014335:Tropomyosin / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism
D003598:Cytoskeletal Proteins; D029721:Drosophila Proteins; D047908:Intracellular Signaling Peptides and Proteins; C097163:Tm2 protein, Drosophila; C490774:Tpm1 protein, mouse; D014335:Tropomyosin; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein