INVESTIGATION ON THE ROLE OF MICAL2 IN MALIGNANT PLEURAL MESOTHELIOMA

Malignant pleural mesothelioma (MPM) is an aggressive cancer with poor prognosis, classified in three hystological subtypes: epithelioid, sarcomatoid, and biphasic. MPM is characterized by the concomitant presence of epithelioid and sarcomatoid (mesenchymal) features; Sarcomatoid type is associated to worse prognosis, suggesting a role of epithelial-mesenchymal transition (EMT) in this dual phenotype (Fassina et al. 2012). EMT is a process by which a polarized epithelial cell undergoes a series of biochemical changes and that results in an elongated and highly migratory mesenchymal phenotype. These changes include the alteration of cell-cell and cell-matrix adhesions and, profound cytoskeletal reorganization, that confer to the cell the ability to move within the extracellular matrix and migrate away from the epithelial layer, in which it originated. Important regulators of cytoskeleton dynamics are the MICAL proteins, a family of monooxygenases able to modify actin. In this way, MICALs may control basic cell phenomena such as adhesion, motility, proliferation/differentiation. In particular, we focused our attention on a member of this family, MICAL2, because studies have shown that MICAL2 is the only family proteins member constitutive active, suggesting that its deregulation might be sufficient to derange its function. Since, in silico analysis show that MICAL2 is expressed in several types of cancer and overexpressed in MPM, we made the hypothesis that its abnormal expression may promote MPM progression. Furthermore our data have shown that MICAL2 was expressed in MPM patients and its expression levels positively correlated with mesothelin (MSLN), an MPM marker, and vimentin (VIM), an EMT marker. To investigate the role of MICAL2 in MPM we used as model MPM cells: the spindle-shaped, MERO-14 and, the mixed epithelial-mesenchymal shaped MERO-25 cell lines, to induce a stable MICAL2 knock-down. MICAL2 abatement in MERO14 cells induces a phenotypic change: from mesenchymal-shape to more epithelial one. Furthermore, our results have shown that the expression levels of SNAI1 and SNAI2 (two EMT-transcription factors), VIM and MSLN, were decreased in MICAL2 knock down (MIC2KD) cells. Furthermore, the expression of SNAI1 and SNAI2 positively correlate with MICAL2 mRNA levels. These findings suggested that MICAL2 could be implicated in EMT process. Our results showed that MERO-14 MIC2KD cells exhibited decreased cell proliferation, adhesion, motility and invasion compared to control cell lines. Moreover, studies suggested that MICAL2 could be an important player in the exosome-release pathway, since some MICAL family membersvare known to interact with the Rab proteins, key regulators of vesicular trafficking and consequently, involved in also in exosomes release. Exosomal markers in kidney cancer 786-O cells-conditioned medium have been identified. Their secretion rate was increased under hypoxia, but exosomal markers were absent in 786-O MIC2KD cells conditioned medium, suggesting that the abatement of MICAL2 may affect also the exosome release. Overall our in vitro preliminary data showed that MICAL2 participate in controlling MPM cells proliferation, adhesion, motility, and exocytosis, probably because it is involved in the regulation of EMT process. Further investigatigation are needed to evaluate MICAL2 as target for anti-cancer therapy.