Di seguito pubblichiamo l'abstract del progetto di ricerca di base della vincitrice della Borsa di Studio 2010 "Alfredo Saiardi!, D.ssa Elisa ten Hacken, con le nostre più vive congratulazioni!

HS1 as a hub molecule between B Cell Receptor and cytoskeleton:
evidences from leukemic B lymphocytes

HS1 is an actin-binding signalling molecule mainly expressed in haematopoietic cells. In T (Gomez et al., Immunity 2006) and NK cells (Butler et al., Nat Immunol 2008), HS1 has been shown to be crucial to initiate membrane-receptors signal transduction pathways, while its function in B cells is poorly defined. Interestingly, the phosphorylation level of HS1 correlates to the clinical course of chronic lymphocytic leukemia (CLL), a B-cell disorder, as the hyperphosphorylated form of HS1 is associated with a more aggressive disease (Scielzo et al., JCI 2005). In addition, in both normal and leukemic B cells, HS1 interacts with cytoskeleton adapters involved in cytoskeletal reorganization (Muzio et al., Leukemia 2007). Moreover, recent work from our lab supports the central role of HS1 in the trafficking, homing and CLL pathogenesis in the leukemic-prone Eu-TCL1 transgenic mouse (Scielzo et al., Blood 2010).

We aimed at elucidating the role of HS1 in B cells by generating an HS1-silenced MEC1 leukemic B-cell line (HS1 KD). First, we performed signalling studies on both control transfected (CNTR) and HS1 KD cells to assess the phosphorylation status of a panel of membrane proximal kinases and of several specific BCR signalling molecules including also downstream effectors and transcription factors. We then analyzed the activation status of other molecules known to be major players in the cytoskeletal reorganization after antigen-receptor engagement and investigated how cytoskeletal remodelling might be affected, at a functional level, by the absence of HS1.

By dissecting the BCR-originated pathway, we show that several signalling molecules are directly affected by HS1 absence. In addition, we report that, in HS1 KD leukemic B cells, the overall amount of phosphoproteins is significantly reduced and, in particular, actin and myosin are less represented in phosphoproteins immunoprecipitates. These evidences suggest that the lack of HS1 may interfere with signalling initiation and sustaining following BCR stimulation also through an impairment in the formation of acto-myosin complexes, that are essential molecular motors in these processes.
These modifications lead to relevant functional abnormalities as in the absence of HS1, leukemic B cells show abnormal cell aggregation, impaired in vitro adhesion and altered migration both in vitro and in vivo.

We are currently analyzing the BCR signalling pathway of primary leukemic B cells purified from CLL patients to test whether a correlation exists between HS1 phosphorylation status and several signalling molecule activation. These studies will allow us to correlate the signalling results with clinical and biological prognostic factors and to eventually identify new HS1 partners that could potentially be exploited to modulate HS1 phosphorylation in CLL cells.