Translation of the radioresistance kinase TLK1B is induced by γ-irradiation through activation of mTOR and phosphorylation of 4E-BP1

Radiation causes a shift in the polysomal distribution of TLK1B mRNA, from the untranslated region and small polysomes to the large polysomes, concomitant with an increase in the expression of TLK1B protein. This change is preceded by an increase in phosphorylation of the eIF4E inhibitory protein 4E-BP1, which releases eIF4E when it is phosphorylated. The phosphorylation of 4E-BP1 depends on mTOR, since rapamycin blocked the increase in phosphorylation induced by radiation, and prevented the increase in TLK1B protein expression. The activation of mTOR was likely due to the rapid activation of Akt following radiation. The activation of Akt could be inhibited with wortmannin, an inhibitor of PI3 kinase, hence placing PI3 kinase upstream of Akt as a very early event following radiation. Wortmannin also inhibited translation of TLK1B mRNA following activation by IR. This was shown both by western blot and by measuring the initiation capacity of the mRNA, as indicated by its distribution on polysomes.The translational upregulation of TLK1B elicited by DNA double strand breaks represents an interesting mechanism of translational regulation of a protein involved in radioprotection and highlights a novel mechanism of the stress response following radiation.The Tousled gene of Arabidopsis Thaliana encodes a protein kinase which, when mutated, results in abnormal flower development characterized by a stochastic loss of floral meristem and organs [1]. Two mammalian Tousled-like kinases (TLK1 and TLK2) were cloned by Sillje et al., 1999 [2] during a PCR-based search for human kinases, who also reported that the activity of these kinases is maximal in S phase, and more recently, these kinases were reported to be targets to checkpoint kinases, ATM and Chk1 [3]. Since ATM and Chk1 are involved in the DNA damage checkpoint upon radiation, this suggests that TLKs may be involved in some aspect of genome surveillance, particularly chromatin remodeling concurrent with DNA repair (see