The anaplastic lymphoma kinase (ALK) gene is characteristically translocated in Anaplastic Large Cell Lymphomas (ALCL) and the juxtaposion of the ALK gene to multiple partners results in its constitutive protein tyrosine kinase activity. We show here that expression of activated ALK induces the constitutive phosphorylation of Stat3 in transfected cells as well as in primary human ALCLs. Furthermore, immunohistochemical studies demonstrate that among distinct human B and T cell lymphomas, activation of Stat3 nuclear translocation is uniquely associated with ALK expression. NPM-ALK also binds and activates Jak3; however, Jak3 is not required for Stat3 activation or for cell transformation in vitro. Moreover, src family kinases are not necessary for NPM-ALK-mediated Stat3 activation or transformation, suggesting that Stat3 may be phosphorylated directly by ALK. To evaluate relevant targets of ALK-activated Stat3, we investigated the regulation of the anti-apoptotic protein Bcl-x L and its role in cell survival in NPM-ALK positive cells. NPM-ALK expression caused enhanced Bcl-x L transcription, largely mediated by Stat3. Increased expression of Bcl-x L provided su cient anti-apoptotic signals to protect cells from treatment with speci®c inhibitors of the Jaks/Stat pathway or the Brc-Abl kinase. These studies support a pathogenic mechanism whereby stimulation of anti-apoptotic signals through activation of Stat3 contributes to the successful outgrowth of ALK positive tumor cells.

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The protein expression of the cyclin-dependent kinase inhibitor p27 is often deregulated in human tumors. In lymphomas the inactivation of p27 is achieved through either increased degradation(1) or sequestration via D cyclins,(2) and p27 protein levels have been shown to have a prognostic significance.(1,3) Recently, S-phase kinase-associated protein 2 (Skp2) has been proved to mediate p27 degradation in normal cells(4-7) and to have oncogenetic properties.(8,9) In this study, B-, T-, and myeloid hematopoietic cell lines and a well-characterized panel of human lymphomas (n = 244) were studied for the expression of Skp2. In human lymphomas, the expression of Skp2 strongly related to the grade of malignancy, being low in indolent tumors and very high in aggressive lymphomas. Moreover, the percentages of Skp2- and S-phase-positive cells, as measured by DNA content or BrdU labeling, strictly matched and closely parallel that of Ki-67 and cyclin A. An inverse correlation between Skp2 and p27 was found in the majority of lymphoma subtypes. Nonetheless, most mantle cell lymphomas and a subset of diffuse large cell lymphomas failed to show this correlation, suggesting that alternative pathway(s) for the regulation of p27 might exist. The detection of Skp2 protein either by flow cytometry or by immunohistochemistry represents a simple method to precisely assess the S phase of lymphomas. The potential diagnostic and prognostic value of Skp2 is discussed.

Fungal virulence mechanisms include adhesion to epithelia, morphogenesis, production of secretory hydrolytic enzymes, and phenotype switching, all of which contribute to the process of pathogenesis. A striking feature of the biology of Candida albicans is its ability to grow in yeast, pseudohyphal, and hyphal forms. The hyphal form plays an important role in causing disease, by invading epithelial cells and causing tissue damage. In this review, we illustrate some of the main hyphae-specific genes, namely HGC1, UME6, ALS3, HWP1, and ECE1, and their relevant and reversed signal transduction pathways in reactions stimulated by environmental factors, including pH, CO2, and serum.

Intracellular factors are involved in and essential for hematopoiesis. HIV-1 Tat-interacting protein of 110 kDa (TIP110; p110 nrb / SART3/p110) is an RNA-binding nuclear protein implicated in the regulation of HIV-1 gene and host gene transcription, premRNA splicing, and cancer immunology. In the present study, we demonstrate a role for TIP110 in the regulation of hematopoiesis. TIP110 was expressed in human CD34 ؉ cells and decreased with differentiation of CD34 ؉ cells. TIP110 mRNA was also expressed in phenotyped mouse marrow hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs). Using TIP110 transgenic (TIP110 TG ) and haploinsufficient (TIP110 ؉/؊ ) mice, we found that increased TIP110 expression enhanced HPC numbers, survival, and cell cycling, whereas decreased TIP110 expression had the opposite effects. Moreover, TIP110 ؉/؊ bone marrow HPCs responded more effectively, and TIP110 TG HPCs less effectively, than those of wild-type control mice to recovery from the cell-cycle-active drug 5-fluorouracil (5-FU). Unexplained sex differences were noted in HSC competitive repopulating ability, but not HPC numbers, in TIP110 TG mice. Intracellularly, TIP110 regulated CMYC and GATA2 expression at the transcriptional level, and TIP110 and CMYC reciprocally regulated the expression of each other. These results demonstrate a role for TIP110 in the regulation of hematopoiesis, effects that are likely linked to TIP110 regulation of CMYC. IntroductionHematopoiesis is regulated at the level of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) via intracellular and extracellular molecules. [1][2][3] Homeostasis is crucial for normal hematopoiesis. 2 Cell cycling of HSCs/HPCs is regulated by growth factors/cytokines, as well as by transcription factors such as C-MYB, CMYC, GATA2, HOX family proteins, and BMI-1. C-MYB promotes HSC growth through induced CMYC. [4][5][6] CMYC induces the expression of positive regulators involved in G1/S cell-cycle transition, and also represses negative regulators of the cell cycle, events required for the proliferation of hematopoietic progenitors. 7 CMYC is involved in cell proliferation and growth, angiogenesis, apoptosis, differentiation, and regulation of chromatin structure, [8][9][10][11] and plays a role in controlling self-renewal and differentiation of HSCs. 12 Tat-interacting protein of 110 kDa (TIP110), which was initially cloned from a human KG-1 myeloid cell line cDNA library, 13 is implicated in RNA metabolism and tumor-antigen presentation. [14][15][16][17] We demonstrated previously that TIP110 regulates the transcription of HIV-1 and cellular genes. 18,19 It is considered a mammalian homolog of the yeast Prp24 protein, and functions as a general pre-mRNA splicing factor. 20 Using molecular, cellular, and genetic strategies, including TIP110 transgenic (TIP110 TG ) and conditional knockout (TIP110 ϩ/Ϫ ) mice, ectopic expression, and shRNA knockdown, we found that TIP110 regulates HPC/HSC function, effects likely involving cell-cycl...

HIV-1 Tat is a major culprit for HIV/neuroAIDS. One of the consistent hallmarks of HIV/neuroAIDS is reactive astrocytes or astrocytosis, characterized by increased cytoplasmic accumulation of the intermediate filament glial fibrillary acidic protein (GFAP). We have shown that that Tat induces GFAP expression in astrocytes and that GFAP activation is indispensable for astrocyte-mediated Tat neurotoxicity. However, the underlying molecular mechanisms are not known. In this study, we showed that Tat expression or GFAP expression led to formation of GFAP aggregates and induction of unfolded protein response (UPR) and endoplasmic reticulum (ER) stress in astrocytes. In addition, we demonstrated that GFAP up-regulation and aggregation in astrocytes were necessary but also sufficient for UPR/ER stress induction in Tat-expressing astrocytes and for astrocyte-mediated Tat neurotoxicity. Importantly, we demonstrated that inhibition of Tat- or GFAP-induced UPR/ER stress by the chemical chaperone 4-phenylbutyrate significantly alleviated astrocyte-mediated Tat neurotoxicity in vitro and in the brain of Tat-expressing mice. Taken together, these results show that HIV-1 Tat expression leads to UPR/ER stress in astrocytes, which in turn contributes to astrocyte-mediated Tat neurotoxicity, and raise the possibility of developing HIV/neuroAIDS therapeutics targeted at UPR/ER stress.

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