INVESTIGADORES
BISIG Carlos Gaston
artículos
Título:
Inhibitors of protein phosphatase 1 and 2A decrease the level of tubulin carboxypeptidase activity associated with microtubules.
Autor/es:
CONTÍN MA, PURRO SA, BISIG CG, BARRA HS, ARCE CA.
Revista:
EUROPEAN JOURNAL OF BIOCHEMISTRY
Referencias:
Año: 2003 vol. DIC p. 4921 - 4929
ISSN:
0014-2956
Resumen:
The association of tubulin carboxypeptidase with microtubules may be
involved in the determination of the tyrosination state of the
microtubules, i.e. their proportion of tyrosinated vs. nontyrosinated
tubulin. We investigated the role of protein phosphatases in the
association of carboxypeptidase with microtubules in COS cells. Okadaic
acid and other PP1/PP2A inhibitors, when added to culture medium before
isolation of the cytoskeletal fraction, produced near depletion of the
carboxypeptidase activity associated with microtubules. Isolation of
the native assembled and nonassembled tubulin fractions from cells
treated and not treated with okadaic acid, and subsequent in vitro
assay of the carboxypeptidase activity, revealed that the enzyme was
dissociated from microtubules by okadaic acid treatment and recovered
in the soluble fraction. There was no effect by nor-okadaone (an
inactive okadaic acid analogue) or inhibitors of PP2B and of tyrosine
phosphatases which do not affect PP1/PP2A activity. When tested in an
in vitro system, okadaic acid neither dissociated the enzyme from
microtubules nor inactivated it. In living cells, prior stabilization
of microtubules with taxol prevented the dissociation of
carboxypeptidase by okadaic acid indicating that dynamic microtubules
are needed for okadaic acid to exert its effect. On the other hand,
stabilization of microtubules subsequent to okadaic acid treatment did
not reverse the dissociating effect of okadaic acid. These results
suggest that dephosphorylation (and presumably also phosphorylation) of
the carboxypeptidase or an intermediate compound occurs while it is not
associated with microtubules, and that the phosphate content determines
whether or not the carboxypeptidase is able to associate with
microtubules.