Tyrosine Kinases and Phosphatases in the Estivating Spadefoot Toad

Abstract

To endure seasonally arid conditions, spadefoot toads (Scaphiopus couchii) spend 9-10 months underground each year in a hypometabolic state, termed estivation. Protein tyrosine kinases (PTKs) and phosphatases (PTPs) were evaluated in organs of control and estivating toads to assess their possible role in signal transduction during estivation. Total PTK activity decreased by 27-52 % in liver, lung and skeletal muscle during estivation but rose by 66% in heart. Total PTP activity changed only in liver (55 % decrease) and heart (74 %increase). Analysis of the distribution of PTKs between cytoplasmic and membrane-associated forms showed that estivation-linked changes in both fractions occurred in heart (increase) and liver (decrease) whereas in lung and skeletal muscle only the soluble fraction was affected. PTPs were assessed using both a general substrate (ENDpYINASL) and a substrate (DADEpYLIPQQG) specific for PTPs containing the SH2 binding site; both revealed estivation-associated changes in activities and subcellular distribution of PTPs in all tissues. DEAE-Sephadex chromatography showed multiple forms of skeletal muscle PTKs and PTPs in both soluble and insoluble fractions. Each fraction showed three major peaks of PTK activity, two of which shifted in elution position during estivation. The data show that PTKs and PTPs are modified in an organ-specific fashion during estivation by three mechanisms: changes in total activity, changes in subcellular distribution and possible protein covalent modification.