Transcriptomic and phylogenetic analysis of Kpna genes: a family of nuclear import factors modulated in xenobiotic-mediated liver growth.

OBJECTIVES: We have identified a member of the karyopherin (importin) alpha family of nuclear import factors as being modulated in rat liver following exposure to the hypolipidaemic and liver growth agent Wy-14,643. To examine the hypothetical role of this protein family as a checkpoint in receptor-mediated signalling, we characterized the rat karyopherin alpha (Kpna) gene family and present cDNA sequences and gene structures for all six rat Kpna genes. Further, we have assembled a comprehensive panel of Kpna coding regions from a range of metazoa, which we have subjected to phylogenetic analysis: This represents by far the most complete phylogenetic study of metazoan karyopherins, including several evolutionary intermediates not previously examined. The phylogeny reveals three Kpna subfamilies with distinct, conserved gene structures, shedding light on the evolutionary origins of this multigene family in metazoa. METHODS AND RESULTS: Using quantitative PCR, we have analysed Kpna transcript levels in 44 rat tissues; Kpna transcripts show a wide variation in their distribution both in absolute and relative terms, suggestive of specialized roles for each member. We also demonstrate that Kpna genes are regulated in rat liver and isolated hepatocytes in a xenobiotic-specific manner for a number of chemically distinct liver growth agents. CONCLUSIONS: In light of the crucial role of nuclear import in mediating the genomic changes elicited through nuclear receptor activation, we postulate that changes in the levels of specific karyopherins alpha during xenobiotic-mediated liver growth represent an important component of the cellular response to the external stimuli that trigger these events.

Quantification of apolipoprotein E receptors in human brain-derived cell lines by real-time polymerase chain reaction.

Apolipoprotein (apo) E4 is a risk factor for Alzheimer's disease (AD) and other neurodegenerative diseases, compared to wild-type apoE3. The mechanism(s) is unknown. One possibility, demonstrated in peripheral tissue cell lines, is that apoE stimulates nitric oxide synthase (NOS) via a receptor-dependent signalling pathway and that apoE4 generates inappropriate amounts of nitric oxide (NO) compared to apoE3. Prior to biochemical investigations, we have quantified the expression of several candidate receptor genes, including low-density lipoprotein-receptor (LDL-r) family members and scavenger receptor class B, types I and II (SR-BI/II), as well as the three NOS isoenzymes and protein kinase B (Akt), in 38 human cell lines, of which 12 derive from brain. Expression of apoE receptor 2 (apoER2), a known signalling receptor in brain, was readily detected in SH-SY-5Y and CCF-STTG1 cells, common models of neurons and astrocytes, respectively, and was highest in H4 neuroglioma, NT-2 precursor cells and IMR-32 neuroblastoma cells. Transcripts of the other lipoprotein receptors were widely, but variably, distributed across the different cell types. Of particular note was the predominant expression of SR-BII over SR-BI in many of the brain-derived cells. As the C-terminus of SR-BII, like apoER2, contains potential SH3 signalling motifs, we suggest that in brain SR-BII functions as a signal transducer receptor.