oxidants and antioxidants in biology - Oxygen Club of California

Molecular variants of the hepatic cytosolic HSP70s:
Relevance for the exercise response
BEATRIZ GONZÁLEZ, MARÍA JESÚS PÉREZ-LORENZO AND
RAFAEL MANSO
Centre of Molecular Biology “Severo Ochoa” (CSIC-UAM). Autonomous
University of Madrid. E-28049 Cantoblanco, Spain
The cytosolic members of HSP70s, the constitutively expressed
(HSP73) and the highly stress inducible (HSP72) proteins,
display at least 3 isoelectric point variants. In non-stressed animals
the hepatic HSP72 levels were very low and only one of the variants
was detected. In exercised animals, when all variants were present,
the two-dimensional patterns were similar for both proteins: a
major variant (1) flanked by one more acidic (2) and a second more
basic (3). The functional relevance of these variants for the hepatic
exercise response was investigated by studying their presence and
relative abundance following a single exercise bout, using the major
variant of the constitutively expressed protein as an internal reference.
The acidic variants of both proteins, HSP72 2 and HSP73 2
increased transitorily shortly after exercise. In contrast with
HSP73 1 , that did not change, the abundance of HSP72 1 increased
during the early post-exercise and its acidic variant, HSP72 2, increased
faster initially (as shown by the HSP72 2 -to-HSP72 1 ratio).
This ratio was also high in the peaks of HSP72 accumulation at 8
and 48 h post-exercise. Incubation of whole liver protein homogenates
with, or without added, alkaline phosphatase or calcineurin increased
the proportion of the basic variants of both proteins by 10-
15 % and reduced that of the acidic ones. Since these transitions
were inhibited by adding a phosphatase inhibitor mix, the data indicate
that the generation of variants of the HSP70s involves phosphorylation/dephosphorylation
processes. However, due to the
relatively small fraction of basic variant that was recovered following
phosphatase treatment, it is difficult to assume that this is
the only mechanism responsible for generating HSP70 variants.
Financed by DGICYT (PB98-0084).
140