Glioblastoma is the most aggressive and invasive adult brain cancer. In glioblastoma, the loss of the tumour suppressor PTEN is the most common genetic alteration resulting in aberrant activation of the PI3-kinase pathway. In Drosophila, the loss of tumour suppressor Lgl results in massive overgrowth of brain tissue that is highly invasive when transplanted into wildtype hosts. Subsequent study of Lgl protein function revealed that it is important for maintenance of cell polarity and neuroblast differentiation through asymmetric cell divisions. It is unclear if inactivation of Lgl occurs in human brain cancers and what role it plays in glioblastoma malignancy. Firstly, this study demonstrated that the loss of PTEN leads to inactivation of Lgl1 via phosphorylation by atypical protein kinase C iota (PKCι). In primary glioblastoma cultures, preventing Lgl1 inactivation by either PTEN expression, PKCι knockdown or expression of non-phosphorylatable Lgl (Lgl3SA) promoted differentiation. In a follow-up study, the effect of active Lgl1 in glioblastoma invasion was investigated. Lgl3SA expression inhibited invasion in vitro through decreased motility. In an orthotopic xenograft mouse model using primary glioblastoma cells, Lgl3SA expression promoted differentiation and decreased invasion. Therefore, PTEN loss, acting via PKCι and Lgl1, has a key role in maintaining glioblastoma in an undifferentiated, highly invasive state similar to what is observed following Lgl loss in Drosophila. PREX1 was investigated as a potential link between PTEN loss and activation of PKCι. PREX1, a Rac activator, is synergistically activated by the PI3-kinase product PIP3 and G protein-coupled receptor (GPCR) βγ subunits. PREX1 expression was detected in primary glioblastoma cell cultures as well as the majority of patient tumour samples. Both PI3-kinase and GPCR βγ subunit activity is required for PREX1 to promote invasion in glioblastoma. In primary glioblastoma cells, Rac1 preferentially associated with Par6a leading to activation of PKCι. Knockdown of PREX1 decreased activation of PKCι. Thus, PREX1 stimulates PKCι activity in glioblastoma likely by modulating the Rac1/Par6a/PKCι complex. The PI3-kinase pathway is activated by mutation in most glioblastomas and these results show this requires a context of GPCR signalling to promote invasion.

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Loss of polarity is a defining characteristic of epithelial cancers. The cytoskeletal proteins, HUGL1 and HUGL2, mediate polarity in epithelial cells through diversified roles in defining membrane identity and trafficking to the basolateral membrane. Importantly, an ortholog of these molecules can inhibit tumor growth in Drosophila, although the mechanisms of their tumor suppressive functions in mammary epithelial cells are unknown. Here, we show nonredundant tumor protective roles for HUGL1 and HUGL2 in human mammary epithelial cells. Using a three dimensional culture system, we report that loss of HUGL1 or HUGL2 causes loss of apicobasal polarity, aberrant growth of multilayered epithelium, nuclear enlargement, loss of membrane identity, and cellular overgrowth. Experiments on plastic also revealed that HUGL1 or HUGL2 loss results in induction of a phenotypic EMT in breast epithelial cells and overexpression of HUGL1 in breast cancer cells reduces proliferation.In a Drosophila model of cancer driven by loss of lgl, we have discovered the consistent dysregulation of a number of miRNAs and mRNAs including the loss of let-7 and miR-9a, which are implicated in breast cancer and associated with the suppression of stem cells. Cross comparisons revealed a set of mRNAs that are both dysregulated in vivo and represent putative targets of the miRNAs changed in lgl mutants. Among these, Thrombospondin, a component of the extracellular matrix was found to be misexpressed in both flies and human cells lacking Lgl. Moreover, genetic interaction experiments showed miR-9a to be a functional effector of lgl in controlling proliferation in the wing. Taken together, the findings reported in this dissertation suggest that HUGL1 and HUGL2 function as tumor suppressors through their roles in polarity and miRNA regulation. These two proteins, functioning as modulators of cell plasticity and promoters of differentiation, are potentially able to control the transition between a differentiated epithelial cell and a cancer stem cell. This research offers new insight into the role of HUGL1 and HUGL2 in breast cancer and reveals novel targets downstream of polarity proteins for therapeutic intervention.

Large granular lymphocyte leukemia (LGLL) represents a rare group of diseases with considerable difficulties in their correct diagnostic workup and therapy. The major challenges lie in their distinction from reactive (including autoimmune) lymphoproliferations. Moreover, monoclonal LGL proliferative diseases are in fact a heterogeneous group of disorders, as recognized by the three subtypes in the current WHO classification. It distinguishes two chronic forms (the focus of this case series), namely T-LGLL and chronic lymphoproliferative disorders of Natural Killer cells (CLPD-NK) as well as aggressive NK-cell leukemia. In the clinical routine, the variable presentations and phenotypes of T-LGLL and CLPD-NK are underappreciated. The relevant differential diagnoses range from benign reactive T-cell expansions to other mature T-cell leukemias to highly aggressive gd-lymphomas. T-LGLL or CLPD-NK patients suffer from a wide variety of symptoms often including, but not limited to, cytopenias or classical autoimmune phenomena. They receive treatments ranging from mere supportive measures (e.g. antibiotics, growth factors, transfusions) over strategies of immunosuppression up to anti-leukemic therapies. The diagnostic pitfalls range from recognition of the subtle T-cell proliferation, repeated establishment of monoclonality, assignment to a descript immunophenotypic pattern, and interpretations of molecular aberrancies. Here, we report a series of selected cases to represent the spectrum of LGLL. The purpose is to raise awareness among the scientifically or practically interested readers of the wide variety of clinical, immunological, and phenotypic features of the various forms of LGLL, e.g. of T-cell type, including its gd forms or those of NK-lineage. We highlight the characteristics and courses of four unique cases from two academic centers, including those from a prospective nationwide LGLL registry. Each case of this instructive catalogue serves to transport a key message from the areas of (chronic inflammatory) contexts in which LGLL can arise as well as from the fields of differential diagnostics and of various treatment options. Implications for optimization in these areas are discussed.

No description available.

Mature T-cell leukemias represent rare, but increasingly recognized diseases of which, compared to their B-cell counterparts, comparatively little is established on their pathogenesis, diagnosis, and treatment. These leukemic post-thymic T-cell neoplasms range from the spectrum of chronic, sometimes debilitating disorders such as T-large granular lymphocytic leukemia (T-LGLL), and related leukemias such as NKLGLL, to more aggressive malignancies such as T- prolymphocytic leukemia (T-PLL). In this series, entitled ‘Pathogenesis, Treatment, and Future Directions for Rare T-cell Leukemias’ we review the current state of the science of these important T-cell neoplasms to inform on their treatment, diagnosis, and pathophysiology.