Requirement for high mobility group protein HMGI-C interaction with STAT3 inhibitor PIAS3 in repression of a-subunit of epithelial Na+ channel (alpha-ENaC) transcription by Ras activation in salivary epithelial cells
Md. Zentner et al., Requirement for high mobility group protein HMGI-C interaction with STAT3 inhibitor PIAS3 in repression of a-subunit of epithelial Na+ channel (alpha-ENaC) transcription by Ras activation in salivary epithelial cells, J BIOL CHEM, 276(32), 2001, pp. 29805-29814
Previously, we have demonstrated that oxidative stress or Ras/ERK activatio
n leads to the transcriptional repression of alpha -subunit of epithelial N
a+ channel (ENaC in lung and salivary epithelial cells. Here, we further in
vestigated the coordinated molecular mechanisms by which alpha -ENaC expres
sion is regulated. Using both stable and transient transfection assays, we
demonstrate that the overexpression of high mobility group protein I-C (HMG
I-C), a Ras/ERK-inducible HMG-I family member, represses glucocorticoid rec
eptor (GR)/dexamethasone (Dex)-stimulated alpha -ENaC/reporter activity in
salivary epithelial cells. Northern analyses further confirm that the expre
ssion of endogenous a-ENaC gene in salivary Pa-4 cells is suppressed by an
ectopic HMGI-C overexpression. Through yeast two-hybrid screening and co-im
munoprecipitation assays from eukaryotic cells, we also discovered the inte
raction between HMGI-C and PIAS3 (protein inhibitor of activated STAT3 (sig
nal transducer and activator of transcription 3)). A low level of ectopical
ly expressed PIAS3 cooperatively inhibits GR/Dex-dependent alpha -ENaC tran
scription in the presence of HMGI-C. Reciprocally, HMGI-C expression also c
oordinately enhances PIAS3-mediated repression of STAT3-dependent transacti
vation. Moreover, overexpression of antisense HMGI-C construct is capable o
f reversing the repression mediated by Ras V12 on GR- and STAT3-dependent t
ranscriptional activation. Together, our results demonstrate that Ras/ERK-m
ediated induction of HMGI-C is required to effectively repress GR/Dex-stimu
lated transcription of alpha -ENaC gene and STAT3-mediated transactivation.
These findings delineate a network of inhibitory signaling pathways that c
onverge on HMGI-C.PIAS3 complex, causally associating Ras/ERK activation wi
th the repression of both GR and STAT3 signaling pathways in salivary epith
elial cells.