Dlk (also termed ZIP kinase) is a novel serine/threonine kinase with a unique C-terminal domain that is rich in arginine and contains three putative NLS motifs and a functional lecuine zipper. Dlk is indeed localized in the nucleus where it shows a speckled distribution. To elucidate the biological functions of Dlk, we wanted to identify the signals relevant for nuclear transport and further the nuclear structures which Dlk binds to. Expression of various deletion and point mutations of Dlk as GFP fusion proteins revealed that the leucine zipper is required for association with speckles and the most C-terminal NLS is necessary and sucient for nuclear transport. Interestingly, a C-terminal deletion mutant defective for nuclear transport exhibited a pronounced colocalization with actin ®laments and, even more strikingly, was a very potent inducer of apoptosis. This apoptotic activity was abrogated, however, when this mutant was retargeted to the nucleus via a heterologous NLS from large T, indicating that Dlk only exerts an apoptotic activity in the cytoplasm. To identify the speckle like structures to which Dlk binds we performed immuno¯uorescence analyses with antibodies directed against representative marker proteins of replication, transcription, or splicing centers. None of these marker proteins revealed a colocalization with Dlk. Instead, we found a partial colocalization with PML bodies which seem to play a key role in regulation of apoptosis. Taken together, these data strongly suggest a functional role for Dlk in control of cell survival which is dependent on its subcellular localization.
We used c-Fos-deficient activated T cells from the spleen and c-Fos-deficient thymocytes to address the capacity of these cells to undergo apoptosis in response to various stimuli. To determine the role of c-Fos in apoptosis regulation in thymocytes, we challenged thymocytes from wild-type and c-Fos-deficient mice with either TPA or the glucocorticoid dexamethasone. After various time points cells were stained according to the Nicoletti method and analyzed by FACS. Thymocytes from both genotypes exhibited similar efficiency of apoptosis in response to treatment with TPA or dexamethasone. Our data provide clear evidence that c-Fos is not required for apoptosis regulation in activated T cells as well as in thymocytes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.