A critical role of tropomyosins in TGF-beta regulation of the actin cytoskeleton and cell motility in epithelial cells.
We have investigated transforming growth factor beta (TGF-beta)-mediated induction of actin stress fibers in normal and metastatic epithelial cells. We found that stress fiber formation requires de novo protein synthesis, p38Mapk and Smad signaling. We show that TGF-beta via Smad and p38Mapk up-regulates expression of actin-binding proteins including high-molecular-weight tropomyosins, alpha-actinin and calponin h2. We demonstrate that, among these proteins, tropomyosins are both necessary and sufficient for TGF-beta induction of stress fibers. Silencing of tropomyosins with short interfering RNAs (siRNAs) blocks stress fiber assembly, whereas ectopic expression of tropomyosins results in stress fibers. Ectopic-expression and siRNA experiments show that Smads mediate induction of tropomyosins and stress fibers. Interestingly, TGF-beta induction of stress fibers was not accompanied by changes in the levels of cofilin phosphorylation. TGF-beta induction of tropomyosins and stress fibers are significantly inhibited by Ras-ERK signaling in metastatic breast cancer cells. Inhibition of the Ras-ERK pathway restores TGF-beta induction of tropomyosins and stress fibers and thereby reduces cell motility. These results suggest that induction of tropomyosins and stress fibers play an essential role in TGF-beta control of cell motility, and the loss of this TGF-beta response is a critical step in the acquisition of metastatic phenotype by tumor cells.
Department of Cancer Genetics, Roswell Park Cancer Institute, Buffalo, NY 14263, USA. andrei.bakin@roswellpark.org
Andrei V
AV
Bakin
Alfiya
A
Safina
Cammie
C
Rinehart
Cecilia
C
Daroqui
Huferesh
H
Darbary
David M
DM
Helfman
D000185:Actinin / Q000235:genetics / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D000818:Animals; D002135:Calcium-Binding Proteins; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects* / Q000502:physiology; D004268:DNA-Binding Proteins / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D020935:MAP Kinase Signaling System / Q000502:physiology; D051379:Mice; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009362:Neoplasm Metastasis; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D051785:Smad Proteins; D022502:Stress Fibers / Q000187:drug effects* / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014335:Tropomyosin / Q000235:genetics / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism; D000096985:Calponins
D000185:Actinin; D000199:Actins; D002135:Calcium-Binding Proteins; D004268:DNA-Binding Proteins; D048049:Extracellular Signal-Regulated MAP Kinases; D008840:Microfilament Proteins; D034741:RNA, Small Interfering; D051785:Smad Proteins; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D014335:Tropomyosin; D048051:p38 Mitogen-Activated Protein Kinases; D018631:ras Proteins; D000096985:Calponins