ACTIVATION OF THE PROTEIN-KINASE-A SIGNAL-TRANSDUCTION PATHWAY BY GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR OR BY GENETIC MANIPULATION REDUCES CYTOSKELETAL ORGANIZATION IN LEWIS LUNG-CARCINOMA VARIANTS
Mri. Young et al., ACTIVATION OF THE PROTEIN-KINASE-A SIGNAL-TRANSDUCTION PATHWAY BY GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR OR BY GENETIC MANIPULATION REDUCES CYTOSKELETAL ORGANIZATION IN LEWIS LUNG-CARCINOMA VARIANTS, International journal of cancer, 56(3), 1994, pp. 446-451
Granulocyte-macrophage colony-stimulating factor (GM-CSF) that is prod
uced by metastatic Lewis lung carcinoma (LLC-LN7) cells functions as a
n autocrine stimulator of tumor-cell motility through protein kinase A
(PKA) signal transduction. This GM-CSF-mediated enhancement of LLC-LN
7 cell motility coincides with a reduction in the level of polymerized
F-actin. In contrast, non-metastatic LLC-C8 tumor cells, which have a
diminished level of PKA signaling, do not produce GM-CSF and do not r
espond to exogenous GM-CSF, since they remain non-motile and retain a
high content of filamentous actin. The capacity of PKA to regulate the
cytoskeletal organization of tumor cells was further studied with the
use of LLC variants that had been stably transfected to over-express
the C-alpha subunit of PKA (CEV cells) or to express a mutant cAMP-res
istant PKA R(I alpha) subunit resulting in a defective PKA (REV cells)
. When compared with wild-type metastatic LLC-LN7 cells, in which the
F-actin staining was too diffuse to be clearly visualized microscopica
lly, the PKA-defective REV-LN7 transfectants had an increased level of
F-actin. In comparison with the wild-type non-metastatic LLC-C8 cells
, which had a high content of F-actin, the CEV-C8 transfectants that o
ver-expressed PKA activity had a reduced level of F-actin. The reduced
polymerization of actin in these CEV-C8 transfectants was accompanied
by reduced levels of the intermediate filament protein vimentin and a
shift in the distribution both of F-actin and of vimentin to the peri
phery of the cells. These results show reduced cytoskeletal organizati
on in metastatic LLC-LN7 cells as compared with that of non-metastatic
LLC-C8 cells, and indicate that elevation of PKA activity, either by
autologous GM-CSF or by genetic manipulation, diminishes cytoskeletal
organization. (C) 1994 Wiley-Liss, Inc.