Aquaporins are a family of homologous membrane proteins that function as highly selective water channels. Aquaporin-5 (AQP5) is uniquely present in lacrimal and salivary glands, where it accounts for normal tear and saliva production. We tested the hypothesis that orally administered human interferon-alpha (HuIFN-alpha) benefits persons with xerostomia by augmenting the production of AQP5 protein by parotid gland epithelium. Cells from three human parotid glands were cultured with and without human lymphoblastoid IFN-alpha, and assayed for AQP5 mRNA levels by reverse transcriptase polymerase chain reaction (RT-PCR), and AQP5 protein levels by Western blot. Intracellular localization of AQP5 protein was done using confocal microscopy. The functional integrity of the glandular tissue was confirmed by RT-PCR analysis of alpha-amylase 1 and basic proline-rich protein transcripts. AQP5 was constitutively expressed in human parotid gland tissue, with AQP5 protein restricted to the plasma membranes and cytoplasmic vesicles of acinar cells. IFN-alpha augmented AQP5 transcription and protein production in a concentration-dependent manner, and increased the size of intensity of staining of AQP5-containing cytoplasmic vesicles in acinar cells. We conclude that IFN-alpha upregulates AQP5 gene expression in human parotid acinar cells in vitro. To our knowledge, this is the first demonstration that IFN-alpha regulates the gene expression of an aquaporin.

The Prep1 homeodomain transcription factor has recently been recognized as a tumor suppressor. Among other features, haploinsufficiency of Prep1 is able to strongly accelerate the B-lymphomagenesis in EμMyc mice. Now we report that this occurs concomitantly with a change in the type of B-cell lymphomas generated by the Myc oncogene. Indeed, the tumors generated in the EμMyc-Prep1+/− mice are much more immature, being mostly made up of Pro-B or Pre-B cells, while those in the EμMyc-Prep1+/+ mice are more differentiated being invariably IgM+. Moreover, we show that Prep1 is in fact required for the differentiation of Pro-B and Pre-B cells into IgM+ lymphocytes and/or their proliferation, thus showing also how a normal function of Prep1 affects EμMyc lymphomagenesis. Finally, we show that the haploinsufficiency of Prep1 is accompanied with a major decrease of Myc-induced apoptosis and that the haploinsufficieny is sufficient for all these effects because the second allele of Prep1 is not lost even at late stages. Therefore, the tumor-suppressive activity of Prep1 is intertwined with both the interference with Myc-induced apoptosis as well as with natural developmental functions of the protein.

A hypomorphic Prep1 mutation results in embryonic lethality at late gestation with a pleiotropic embryonic phenotype that includes defects in all hematopoietic lineages. Reduced functionality of the hematopoietic stem cells (HSCs) compartment might be responsible for the hematopoietic phenotype observed at mid-gestation. In this paper we demonstrate that Prep1 regulates the number of HSCs in fetal livers (FLs), their clonogenic potential and their ability to de novo generate the hematopoietic system in ablated hosts. Furthermore, we show that Prep1 controls the self-renewal ability of the FL HSC compartment as demonstrated by serial transplantation experiments. The premature exhaustion of Prep1 mutant HSCs correlates with the reduced quiescent stem cell pool thus suggesting that Prep1 regulates the self-renewal ability by controlling the quiescence/proliferation balance. Finally, we show that in FL HSCs Prep1 absence induces the interferon signaling pathway leading to premature cycling and exhaustion of fetal HSCs.

Prep1 and Meis1 ortholog TALE transcription factors have opposing roles in tumorigenesis: Meis1 serves as an oncogene, Prep1 as a tumor suppressor. We now report that, Meis1 overexpression in primary Prep1-deficient (Prep1i/i) embryonic hematopoietic cells increases self-renewal potential of cells in vitro but not in vivo, whereas leukemia is instead obtained when Meis1 is combined with another oncogene, HoxA9. Prep1i/i Meis1-HoxA9-generated leukemic cells are less differentiated and grow more aggressively after the second passage in the mouse. These data indicate that Prep1 represents a barrier to the transforming activity of Meis1 in vitro, but its absence is not sufficient to induce early leukemogenesis. On the other hand, the Prep1i/i background appears to favor the insurgence of mutations that cause a more aggressive Meis1-HoxA9-generated leukemia. Indeed, the Prep1i/i leukemic cells upregulate the Polycomb protein Bmi-1 and expectedly down-regulate the Ink4a/Arf locus products. Finally, an important feature contributed by the Prep1i/i background is the post-transcriptional increase in Meis1 protein level.

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