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Activation of the RET gene by chromosomal rearrangements generating RET/PTC oncogenes is a frequent, early, and causative event in papillary thyroid carcinoma (PTC). We have previously shown that, in human primary thyrocytes, RET/PTC1 induces a transcriptional program including the MET proto-oncogene. In PTCs, beta-catenin is frequently mislocated to the cytoplasm nucleus. We investigated the interplay between Ret/ptc1 signaling and Met in regulating the proinvasive phenotype and beta-catenin localization in cellular models of human PTC. Here, we show that Met protein is expressed and is constitutively active in human thyrocytes exogenously expressing RET/PTC1 as well as a mutant (Y451F) devoid of the main Ret/ptc1 multidocking site. Both in transformed thyrocytes and in the human PTC cell line TPC-1, Ret/ptc1-Y451-dependent signaling and Met cooperated to promote a proinvasive phenotype. Accordingly, gene/functional silencing of either RET/PTC1 or MET abrogated early branching morphogenesis in TPC-1 cells. The same effect was obtained by blocking the common downstream effector Akt. Y451 of Ret/ptc1 was required to promote proliferation and nuclear translocation of beta-catenin, suggesting that these oncogene-driven effects are Met-independent. Pharmacologic inhibition of Ret/ptc1 and Met tyrosine kinases by the multitarget small molecule RPI-1 blocked cell proliferation and invasive ability and dislocated beta-catenin from the nucleus. Altogether, these results support that Ret/ptc1 cross talks with Met at transcriptional and signaling levels and promotes beta-catenin transcriptional activity to drive thyrocyte neoplastic transformation. Such molecular network, promoting disease initiation and acquisition of a proinvasive phenotype, highlights new options to design multitarget therapeutic strategies for PTCs.

Chronic and persistent inflammation contributes to cancer development and can predispose to carcinogenesis. Infection-driven inflammations are involved in the pathogenesis of approximately 15-20% of human tumors. However, even tumors that are not epidemiologically linked to pathogens are characterized by the presence of an inflammatory component in their microenvironment. Hallmarks of cancer-associated inflammation include the presence of infiltrating leukocytes, cytokines, chemokines, growth factors, lipid messengers, and matrix-degrading enzymes. Schematically, two interrelated pathways link inflammation and cancer: (1) genetic events leading to neoplastic transformation promote the construction of an inflammatory milieu; (2) tumor-infiltrating leukocytes, in particular macrophages, are prime regulators of cancer inflammation. Thus, an intrinsic pathway of inflammation (driven in tumor cells), as well as an extrinsic pathway (in tumor-infiltrating leukocytes) have been described and both contribute to tumor progression.

The receptor tyrosine kinase RET, with a known role in embryonic development and in human pathologies, is alternatively spliced to yield at least two functional isoforms, which differ only in their carboxyl terminal. Enigma protein is a member of the PDZ-LIM family and is known to interact with the short isoform of RET/PTC2, a chimeric oncoprotein isolated from papillary thyroid carcinoma. Here, we show that Enigma also interacts in intact cells with the short isoform of RET-wt and of its pathologic mutants associated to MEN2 syndromes, RET-C634R and RET-M918T. In contrast, Enigma binds all the corresponding RET long isoforms very poorly and colocalizes with short but not long RET/PTC2 isoforms. The RET docking tyrosine for Enigma is the last but one before the divergence between the two isoforms and we demonstrated that short-isoform-specific amino acid residues +2 to +4 to this tyrosine are required for the interaction of RET/PTC2 with Enigma.

The satellite bacteriophage P4, in the presence of a helper phage, can enter either the lytic or the lysogenic cycle. In the absence of the helper, P4 can integrate in the bacterial chromosome. In addition, the partially immunity-insensitive mutant P4 vir1 can be maintained as a plasmid. We have found that in the absence of the helper, P4 wt also can be maintained as a plasmid, and that both P4 wt and P4 vir1 have two options for their intracellular propagation: a repressed-integrated or a derepressed-high copy number plasmid mode of maintenance. In the repressed mode, the P4 wt genome is only found integrated into the bacterial chromosome, while the P4 vir1 is found also as a low copy number plasmid coexisting with the integrated P4 vir1 genome. The clones carrying P4 in the derepressed-high copy number plasmid state are obtained at low frequency (0.3%) upon infection with P4 wt, while the vir1 mutation increases this frequency about 300-fold. Such clones can be distinguished easily because of their typical colony morphology (rosettes), due to the presence of filamentous cells. Filamentation of the bacterial host suggests that the presence of derepressed P4 genomes in high copy number interferes with the normal cell division mechanism. The derepressed clones are rather stable, but may revert spontaneously to the repressed state. Spontaneous transition from the repressed to the derepressed state was not observed; however, it can be induced by P2 or P4 vir1 superinfection of P4 wt and P4 vir1 lysogens or by growing the P4 vir1 lysogens up to the late exponential phase. The ability of P4 to choose either of two stable states and the potential to shift between these two modes of propagation indicate that the synthesis of the immunity repressor is regulated.