MacDonald, J.A. and Storey, K.B. 2007. The effects of
hibernation on protein phosphatases from ground squirrel organs. Arch. Biochem.
Biophys. 468, 234-243. DIO: 10.1016/j.abb.2007.10.005
The effects
of hibernation on protein phosphatases from ground squirrel organs.
Justin
A. MacDonald and Kenneth B. Storey
Abstract
Protein
phosphorylation has been identified as a reversible mechanism for the regulated
suppression of metabolism and thermogenesis during mammalian hibernation. The
effects of hibernation on the activity of serine/threonine and tyrosine protein
phosphatases (PP1, PP2A, PP2C and PTPs) were assessed
in five organs of Richardson’s ground squirrel. Each phosphatase subfamily
responded differently during torpor, and each showed organ-specific patterns of
activity changes. The distribution of PP1 catalytic subunit (PP1c) isoforms (a,
d, c1) was assessed in five organs, and changes in the subcellular distribution
of PP1 were observed during hibernation in liver and muscle. For example, in
muscle, cytosolic PP1 content increased and myofibril-associated PP1 decreased
during torpor. PP1c from ground squirrel liver was purified to homogeneity and
characterized; temperature effects on PP1c maximal activity suggested that
temperature had little or no effect on relative dephosphorylation potential at
low temperatures. However, nucleotide inhibition of PP1c by ATP, ADP and AMP
was much weaker at 5°C compared with 37°C assay temperatures. PP2A activity
decreased in three organs (brown adipose, kidney, brain) during
hibernation whereas PP2C activity was increased in liver and brain. PTPs were assessed using both a general substrate (ENDpYINASL) and a substrate (DADEpYLIPQQG)
specific for PTPs containing the SH2-binding site;
both revealed hibernation-associated changes in PTP activities. Changes in
protein phosphatase activities suggest the relative importance of these modules
in controlling metabolic function and cellular processes during mammalian
hibernation.