INVESTIGADORES
GALIGNIANA Mario Daniel
artículos
Título:
Tautomycin inhibits phosphatase-dependent transformation of the rat kidney mineralocorticoid receptor
Autor/es:
PIWIEN-PILIPUK G, GALIGNIANA MD
Revista:
MOLECULAR AND CELLULAR ENDOCRINOLOGY.
Editorial:
ELSEVIER IRELAND LTD
Referencias:
Lugar: Amsterdam; Año: 1998 vol. 144 p. 119 - 130
ISSN:
0303-7207
Resumen:
The binding of aldosterone (ALDO) to the mineralocorticoid receptor (MR)
induces a conformational change of the protein referred to as
'transformation'. This feature can be evidenced in vivo by the capacity
of the MR to interact with chromatin, and in vitro by the ability of the
MR to bind to DNA strands or to shift the sedimentation coefficient (S)
to lower values. The transformation process allows MR to work as a
transcription factor after interacting with specific sequences of DNA.
The signal transduction pathway for the MR transformation remains
unknown. As a first step towards elucidating the mechanism of
steroid-dependent MR transformation, we asked if the MR-signaling
pathway is affected by the phosphorylation status of the
MR-heterocomplex, and how that pathway may be regulated. Incubation of
preformed [3H]ALDO-MR complex with bovine intestinal alkaline
phosphatase led to an increase in the rate of MR-transformation
(measured as 9.4-5.4S shift). This alkaline phosphatase-dependent MR
transformation was inhibited by the specific alkaline phosphatase-type
inhibitor levamisole, and was not evident in incubations performed with
acid phosphatases. A direct correlation between the DNA-cellulose
binding capacity of the [3H]ALDO-MR complex and the percentage of
transformed 5.4S MR form was also observed. When rat kidney cytosol was
incubated in the absence of both exogenous phosphatase and stabilizing
agents (such as molybdate or vanadate), MR transformation also took
place, in a time- and temperature-dependent process. In contrast with
the inhibitory effect observed upon alkaline phosphatase-promoted
transformation, levamisole was unable to inhibit the endogenous
transforming activity of MR, suggesting that an endogenous phosphatase
other than those which belong to the alkaline-type may be responsible
for that transformation. Tautomycin, a polyketide produced by the soil
bacteria Streptomyces which inhibits serine/threonine phosphatases of
the PP1/PP2A subgroup, was able to inhibit the endogenous phosphatase
activity in a concentration-dependent form (Ki(app)=7.35 nM). These
results support the idea that the endogenous renal activity involved in
the regulation of rat kidney MR transformation may be a protein
phosphatase which belongs to the PP1/PP2A subgroup.