Exosomes are vesicles secreted by most hematopoietic cells on fusion of multivesicular endosomes with the plasma membrane. Many studies have reported that exosomes may also be released by tumor cells. Exosomes are believed to play an antitumor role through immune cells. We asked whether tumor exosomes have biological activities on tumor cells. We report that human pancreatic tumor nanoparticles, exosome-like as characterized by proteomic analyses and rich in lipid rafts, decreased tumor cell proliferation. Nanoparticles increased Bax and decreased Bcl-2 expressions. Caspase-3 and -9 but not caspase-8 inhibitors impaired apoptosis, which implicates the mitochondria apoptotic pathway. The ceramide-sphingomyelin apoptotic pathway was inoperative. Moreover, nanoparticles induced phosphatase and tensin homolog (PTEN) and glycogen synthase kinase (GSK) -3beta activation and decreased pyruvate dehydrogenase activity. In nanoparticle-treated cells, PTEN formed complexes with actin, beta-catenin, and GSK-3beta. Thus, beta-catenin may no longer be available to activate the survival pathway. Nanoparticles triggered the down-regulation of cyclin D1 and poly(ADP-ribose) polymerase. Hence, nanoparticles counteracted the constitutively activated phosphatidylinositol 3-kinase/Akt survival pathway to drive tumor cells toward apoptosis. Our study provides the first evidence of an apoptotic function of tumor-derived nanoparticles on tumor cells. We propose a new role for nanoparticles, i.e., as signal carriers for interaction between cells, which may have implications in physiopathological situations.

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We have isolated the basement membrane component nicein and performed rotary-shadow analyses using electron microscopy that showed the presence of two forms (I and 11) of the protein. Molecular cloning of the cDNA that codes for the 100-kDa chain of the protein revealed that the sequence matches those independently identified for the 105 -155-kDa subunit of kalinin, a recently identified basement membrane component. These data demonstrate that nicein and kalinin contain an identical chain. The length of the open reading frame in the cDNA (~5 2 0 0 nucleotides) and amino acid sequences obtained from the N-terminus of the 105-kDa kalinin chain showed the occurrence of a precursor polypeptide. This immature polypeptide is probably related to form I, observed by rotary shadowing, while the mature form is related to form II. It is noteworthy that niceinkalinin subunits share discrete sequence similarities with the B2 chain of human laminin, but with a cleavage occurring within domain 111 that eliminates domains IV and V from the final product. The sequence of this subunit is nearly identical to that of B2t, a recently described polypeptide supposed to be related to a new laminin variant. Since niceinkalinin expression is specifically impaired in the severe genodermatosis Herlitz junctional epidermolysis bullosa, the role and structure of this tissue-restricted laminin variant is crucial for the understanding of epidermal-dermal adhesion.The basement membrane (BM) is a type of extracellular matrix which provides an attachment substrate for overlying cell populations and plays a crucial role in organizing tissue architecture, tissue compartmentalization, differentiation of adjacent cells and filtration of nutrients. Since mechanisms mediating these functions are poorly understood, a considerable amount of research has been devoted to the molecular characterization of BM components and elucidation of their biochemical properties. Some differences exist from one type of BM to another and no less than 14 shared macromolecules have already been found [l].We previously reported the isolation of a novel epidermal BM component, called nicein, which is found in various BM species that we investigated with the monoclonal antibody GB3 [2, 31. This glycosylated protein is composed of three major subunits of 100,125 and 150 kDa, as shown by immunoprecipitation assays performed on keratinocytes in culture [3]. Since nicein is secreted by these cells, we isolated the protein by immunoaffinity chromatography from conditioned

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