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2015 ; 10
(3
): e0121589
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Actin-mediated gene expression depends on RhoA and Rac1 signaling in proximal
tubular epithelial cells
#MMPMID25816094
Giehl K
; Keller C
; Muehlich S
; Goppelt-Struebe M
PLoS One
2015[]; 10
(3
): e0121589
PMID25816094
show ga
Morphological alterations of cells can lead to modulation of gene expression. An
essential link is the MKL1-dependent activation of serum response factor (SRF),
which translates changes in the ratio of G- and F-actin into mRNA transcription.
SRF activation is only partially characterized in non-transformed epithelial
cells. Therefore, the impact of GTPases of the Rho family and changes in F-actin
structures were analyzed in renal proximal tubular epithelial cells. Activation
of SRF signaling was compared to the regulation of a known MKL1/SRF target gene,
connective tissue growth factor (CTGF). In the human proximal tubular cell line
HKC-8 overexpression of two actin mutants either favoring or preventing the
formation of F-actin fibers regulated SRF-mediated transcription as well as CTGF
expression. Only overexpression of constitutively active RhoA activated
SRF-dependent gene expression whereas no effect was detected upon overexpression
of Rac1 mutants. To elucidate the functional role of Rho kinases as downstream
mediators of RhoA, pharmacological inhibition and genetic inhibition by transient
siRNA knock down were compared. Upon stimulation with lysophosphatidic acid (LPA)
Rho kinase inhibitors partially suppressed SRF-mediated transcription, whereas
interference with Rho kinase expression by siRNA reduced activation of SRF, but
barely affected CTGF expression. Together with the partial inhibition of CTGF
expression by the pharmacological inhibitors Y27432 and H1154, Rho kinases seem
to be less important in mediating RhoA signaling related to CTGF expression in
HKC-8 epithelial cells. Short term pharmacological inhibition of Rac1 activity by
EHT1864 reduced SRF-dependent CTGF expression in HKC-8 cells, but was overcome by
a stimulatory effect after prolonged incubation after 4-6 h. Similarly, human
primary cells of proximal but not of distal tubular origin showed inhibitory as
well as stimulatory effects of Rac1 inhibition. Thus, RhoA signaling activates
MKL1-SRF-mediated CTGF expression in proximal tubular cells, whereas Rac1
signaling is more complex with adaptive cellular responses.