INVESTIGADORES
CANEPA Eduardo Tomas
artículos
Título:
Phosphatidylinositol 3-kinase and Ras/Mitogen-activated protein signaling pathways are required for the regulation of 5-aminolevulinate synthase gene expression by insulin
Autor/es:
MARÍA E. SCASSA; ALEJANDRA S. GUBERMAN; CECILIA L. VARONE; EDUARDO T. CÁNEPA
Revista:
EXPERIMENTAL CELL RESEARCH
Editorial:
Elsevier
Referencias:
Año: 2001 vol. 271 p. 201 - 213
ISSN:
0014-4827
Resumen:
Insulin regulates the expression of several hepatic
genes. Although the general definition of insulin signaling
has progressed dramatically, the elucidation of
the complete signaling pathway from insulin receptor
to transcription factors involved in the regulation of a
specific gene remains to be established. In fact, recent
works suggest that multiple divergent insulin signaling
pathways regulate the expression of distinct
genes. 5-Aminolevulinate synthase (ALAS) is a mitochondrial
matrix enzyme that catalyzes the first and
rate-limiting step of heme biosynthesis. It has been
reported that insulin caused the rapid inhibition of
housekeeping ALAS transcription, but the mechanism
involved in this repression has not been explored. The
present study investigates the role of phosphatidylinositol
3-kinase (PI3-kinase) and mitogen-activated protein
kinase pathways in insulin signaling relevant to
ALAS inhibition. To explore this, we combined the
transient overexpression of regulatory proteins involved
in these pathways and the use of small cell
permeant inhibitors in rat hepatocytes and HepG2
cells. Wortmannin and LY294002, PI3-kinase inhibitors,
as well as lovastatin and PD152440, Ras farnesylation
inhibitors, and MEK inhibitor PD98059 abolished
the insulin repression of ALAS transcription.
The inhibitor of mTOR/p70S6K rapamycin had no effect
whatsoever upon hormone action. The overexpression
of vectors encoding constitutively active Ras, MEK, or
p90RSK mimicked the inhibitory action of insulin. Conversely,
negative mutants of PKB, Ras, or MEK impaired
insulin inhibition of ALAS promoter activity.
Furthermore, inhibition of one of the pathways blocks
the inhibitory effect produced by the activation of the
other. Our findings suggest that factors involved in
two signaling pathways that are often considered to be
functionally separate during insulin action, the Ras/
ERK/p90RSK pathway and the PI3K/PKB pathway, are
jointly required for insulin-mediated inhibition of
ALAS gene expression in rat hepatocytes and human
hepatoma cells.S6K rapamycin had no effect
whatsoever upon hormone action. The overexpression
of vectors encoding constitutively active Ras, MEK, or
p90RSK mimicked the inhibitory action of insulin. Conversely,
negative mutants of PKB, Ras, or MEK impaired
insulin inhibition of ALAS promoter activity.
Furthermore, inhibition of one of the pathways blocks
the inhibitory effect produced by the activation of the
other. Our findings suggest that factors involved in
two signaling pathways that are often considered to be
functionally separate during insulin action, the Ras/
ERK/p90RSK pathway and the PI3K/PKB pathway, are
jointly required for insulin-mediated inhibition of
ALAS gene expression in rat hepatocytes and human
hepatoma cells.RSK mimicked the inhibitory action of insulin. Conversely,
negative mutants of PKB, Ras, or MEK impaired
insulin inhibition of ALAS promoter activity.
Furthermore, inhibition of one of the pathways blocks
the inhibitory effect produced by the activation of the
other. Our findings suggest that factors involved in
two signaling pathways that are often considered to be
functionally separate during insulin action, the Ras/
ERK/p90RSK pathway and the PI3K/PKB pathway, are
jointly required for insulin-mediated inhibition of
ALAS gene expression in rat hepatocytes and human
hepatoma cells.RSK pathway and the PI3K/PKB pathway, are
jointly required for insulin-mediated inhibition of
ALAS gene expression in rat hepatocytes and human
hepatoma cells.