The Dstpk61 locus of Drosophila produces multiple transcripts and protein isoforms, suggesting it is involved in multiple signalling pathways

Abstract

The Drosophila gene Dstpk61 encodes a serine threonine protein kinase homologous to human phosphoinositidedependent protein kinase (PDK1), and also has homologues in S. cerevisiae, S. pombe, C. elegans, A. thaliana, mouse, and sheep. Where its function has been investigated, this kinase is thought to be involved in regulating cell growth and survival in response to extracellular signals such as insulin and growth factors. In Drosophila it produces multiple transcripts, some of which appear to be sex-specific.In addition to the five Dstpk61 cDNAs we have described previously we report the existence of a further 18 expressed sequence tag (EST) cDNAs, three of which we have fully sequenced. We conclude that Dstpk61 is a complex locus that utilises a combination of alternative promoters, alternative splice sites and alternative polyadenylation sites to produce a vast array of different transcripts. These cDNAs encode at least four different DSTPK61 protein isoforms with variant N-termini. In this paper, we discuss the possible functions of the distinct Dstpk61 transcripts and how they might be differentially regulated. We also discuss the roles that DSTPK61 protein isoforms might play in relation to the protein domains they contain and their potential targets in the cell. Finally, we report the putative structure of the human PDK1 gene based on computer comparisons of available mRNA and genomic sequences. The value of using sequence data from other species for experimental design in mammalian systems is discussed.

Nuclear translocation of 3′-phosphoinositide-dependent protein kinase 1 (PDK-1): A potential regulatory mechanism for PDK-1 function

“…This finding suggests that PDK-1 may be a cytoplasmic-nuclear-shuttling protein. Consistent with this hypothesis, it has been reported that Drosophila PDK-1 possesses a putative bipartite nuclear localization signal (16) that is also conserved in the mouse and human protein. To examine whether PDK-1 undergoes nuclear translocation, we treated CHO͞IR cells expressing Myc-mPDK-1 with leptomycin B (LMB), a specific inhibitor of CRM1-mediated nuclear export (21,22).…”

“…These observations suggest that an intact PI3-kinase pathway may be reconstituted in the nucleus to regulate nuclear events such as gene transcription. Sequence analysis of Drosophila PDK-1 Dstpk61 revealed the presence of a putative bipartite nuclear localization signal (16). In this study, we demonstrate that PDK-1 is a cytoplasmic-nuclear-shuttling protein.…”

A New Molecular Target of Insulin Action: Regulating the Pivotal PDK1

“…In Drosophila, the DSTPK61 gene produces multiple transcripts that encode for at least four different protein isoforms with variant N-termini [44,45]. Analysis of PDK1 cDNAs isolated from human [37], rat [20] and mouse [25] suggests that mammalian pdk1 may similarly give rise to alternatively spliced transcripts.…”