Parallel Sessions (Proffered Papers)

The Microtubule Affinity-Regulating Kinase 4 belongs to a kinases family that phosphorylates the Microtubule[MT]-Associated Proteins, causing their detachment and increasing MT dynamics. MARK4 encodes two alternative spliced isoforms, L and S, which expression is differentially regulated in human tissues. In normal brain the predominant expression of MARK4S has been related to a putative role in neuronal differentiation; the L isoform has been conversely found highly expressed in neural progenitors and in gliomas, as well as in hepatocarcinoma cell lines, highlighting a general role in neoplastic transformation. The current study aimed at better defining the role of MARK4 L and S in gliomagenesis. The expression levels of these isoforms were investigated by Q-PCR and WB on 50 gliomas (low and high grade tumors and cell lines) and 8 cancer stem cell lines (CSC), in addition to normal brain, neural stem cells (NSC) and neural progenitors. Array-CGH and mutation analysis failed to reveal any genomic alteration. Expression profiling of MARK4 L and S in glioma highlighted a predominant expression of the L isoform in parallel with a significant decrease of the S levels, that correlate with tumor grading, suggesting a change in the ratio between the two isoforms during glioma progression. These findings let us hypothesize an involvement of alternative splicing in regulating the relative expression of the two isoforms in normal cells, that could be altered in gliomagenesis. Evaluation of MARK4 expression levels in CSC vs NSC showed that the S isoform is slightly detectable; conversely, a significantly higher expression of MARK4L is estimated in a subset of CSC, strengthening a role of MARK4L in glioma tumorigenesis. We found that the anti-MARK4L antibody stains in vivo cells in human and mouse embryonic ventricular zone and in mouse adult sub-ventricular zone (SVZ), well known regions of stem cells localization, thus delineating MARK4L as a stemness marker with potential tumorigenic ability. This evidence, together with the retrieval of MARK4L altered expression in glioma, reinforces the stem cell hypothesis on the origin of glial tumor, at least glioblastoma (GBM). We are currently investigating paraffin-embedded glioma sections to correlate MARK4L localization to the region of tumor formation, also by evaluating MRI features of GBMs in relation to the SVZ. [Supported by a grant from the Associazione Italiana per la Ricerca sul Cancro]