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1 Biology, York University, Toronto, Canada
2 Kinesiology and Health Science, York University, Toronto, Canada
3 Biology, York University, Toronto, Canada; Kinesiology and Health Science, York University, Toronto, Canada
* To whom correspondence should be addressed. E-mail: dhood{at}yorku.ca.
Thyroid hormone (T3) regulates the function of many tissues. The effects of T3 have largely been attributed to the modulation of thyroid hormone receptor (TR)-dependent gene transcription, however non-genomic actions of T3 via the initiation of signaling events are emerging in a number of cell types. This study investigated the ability of short-term T3 treatment to phosphorylate and activate signaling proteins in rat tissues in vivo. The kinases investigated included p38, AMPK and ERK1/2. Following 2h of T3 treatment, p38 and AMPK phosphorylation was increased in both the slow-twitch soleus and the fast-twitch plantaris muscles. In contrast, ERK1/2 was not activated in either tissue. Neither p38 nor AMPK was affected in heart, however AMPK activation was decreased by T3 in liver. ERK1/2 activation was decreased by T3 in heart, but increased in liver. Possible downstream consequences of T3-induced kinase phosphorylation were investigated by measuring CREB and TR DNA-binding, as well as PGC-1
mRNA levels. Protein-DNA binding to the cAMP or thyroid hormone response elements was unaltered by T3. However, PGC-1 mRNA expression was increased following 12 hours of T3 treatment in soleus. These data are the first to characterize the effects T3 treatment on kinase phosphorylation in vivo. We show that T3 rapidly modifies kinase activity in a tissue-specific fashion. Moreover, the T3-induced phosphorylation of p38 and AMPK in both slow- and fast-twitch skeletal muscles suggests that these events may be important in mediating hormone-induced increases in mitochondrial biogenesis in skeletal muscle.
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