ABROGATION OF EMILIN1-alpha4beta1 INTEGRIN INTERACTION AFFECTS EXPERIMENTAL COLITIS AND COLON CARCINOGENESIS ENHANCING LYMPHATIC DYSREGULATION AND INCREASING INFLAMMATORY CASCADE

Colitis-associated cancer (CAC) is one of the principal cancer types in which there is a functional link between inflammation, tumor microenvironment and cancer progression; moreover, it is related to striking changes in the lymphatic vasculature. Development of aberrations that promote tumour initiation is strongly influenced by the contextual microenvironment. The extracellular matrix (ECM) glycoprotein EMILIN-1 is expressed, among several other tissues, in the normal colonic mucosa and exerts a lot of important function associated to its different domains. Most important, EMILIN-1 is a key structural element in the preservation of the integrity of lymphatic vessels (LVs). It is an adhesive ligand of a4b1 and a9b1 integrins via its gC1q domain; this interaction down-regulates cell proliferation unlike from signals generated by ligand-activated integrins that in general favor proliferative processes. a4b1 integrin plays an important role during inflammation and it is expressed in the normal colon but in colon adenomas and carcinomas is moderately or highly expressed, respectively. Thanks to all the structural and functional properties exerted by EMILIN-1, we hypothesized that it could be located in the context of the development of inflammatory colon cancer. In order to investigate how EMILIN-1 properties are crucial to control proliferation and to guarantee the regeneration of a competent and well-functioning lymphatic vasculature, we took advantage from an Emilin1-/- (E1-/-) mouse model and an E933A EMILIN-1 transgenic mouse model (E1-/-/E1-E933A), in which a mutant EMILIN-1, unable to be engaged by a4b1, is expressed. After a two-steps colon carcinogenesis induction, E1-/- and E1-/-/E1-E933A mice displayed higher tumour incidence, bigger and less differentiated adenomas and lower survival in comparison with E1+/+ littermates, suggesting a protective anti-proliferative effect in the colon microenvironment exerted by “functional” EMILIN-1. The contribution of inflammation was then analysed after induction of chronic experimental colitis. E1-/- and E1-/-/E1-E933A mice presented higher clinical and endoscopic colitis scores and more severe mucosal injury, fibrosis and inflammation than E1+/+ counterparts. Furthermore E1-/- and E1-/-/E1-E933A mice showed an extensive epithelial damage and an increased infiltration of inflammatory cells in the lamina propria, an up-regulation of several inflammatory response genes and a down-regulation of cell-cell adhesion molecule. Even without colitis induction, E1-/- and E1-/-/E1-E933A colonic LVs presented morphologic and functional alterations: they formed a dense network and appeared irregular, dilated and leaky. Under inflammatory conditions E1+/+ displayed a normal pro-lymphangiogenic capacity, whereas E1-/- and E1-/-/E1-E933A showed a reduced number of podoplanin positive vessels and also functional lymphatics impairment. All these results, mostly obtained using transgenic mouse model, allow us to postulate that the local inflammatory response and the consequences on EMILIN-1 structural and regulatory functions could be important events favouring CAC initiation. In an inflammatory colon cancer contest, an unfunctional gC1q domain, as a consequence of degradation by proteolytic enzymes, very likely leads to the loss of EMILIN-1 oncosoppressor properties. Moreover, an EMILIN-1 deficient or mutated protein, favours lymphatic disfunction and metastatic spread that in turn could impair the inflammatory cells drainage with a consequent unresolved inflammation. Avoiding the EMILIN-1 (specifically its gC1q domain) impairment, could represent a novel pharmacological and therapeutic approach: the attempts to block or prevent EMILIN1 degradation could be the basis for a novel ECM strategy aimed to rescue the anti-proliferative properties of EMILIN-1, promote lymphatic function and avoid dysregulation in inflammatory colon cancer.