Regulation of TGFβ signaling by long non-coding RNAs and ADP-ribosylation

Transforming growth factor β (TGFβ) signaling pathways participate in embryonic development and tissue homeostasis and have a dual role in cancer. TGFβ acts as a tumor suppressor that promotes cell cycle arrest and apoptosis at initial stages of tumorigenesis. In contrast, TGFβ, induces epithelial to mesenchymal transition (EMT), a normal embryonic process which is employed by advanced cancers, in order to acquire mesenchymal traits and metastasize. Bone morphogenetic protein (BMP) family members belong to the TGFβ superfamily and are involved in cell differentiation, development and bone formation. Non-coding RNAs (ncRNAs) are not translated into proteins, are important regulators of gene expression and physiological processes and are often de-regulated in cancer. They control gene expression through physical association with chromatin, DNA, RNA molecules or proteins. Poly(ADP-ribose) polymerases (PARPs) catalyze the poly (ADP)-ribosylation of proteins, whereas the enzyme poly(ADP-ribose) glycohydrolase (PARG) removes ADP-ribose units. Members of the PARP family function in the DNA damage response, regulation of transcription and cell death. In this thesis, we investigated the importance of the TGFβ signaling pathway in regulating the expression of long non-coding RNAs (lncRNAs). We identified TGFβ-regulated lncRNAs and observed that a substantial number of them act in a feedback loop to modulate the magnitude of TGFβ signaling. Interestingly, the nuclear lncRNA TGFB2-antisense RNA 1 (TGFB2-AS1) is induced by TGFβ and negatively regulates expression of members of the TGFβ and BMP pathways, through interaction with EED, a protein of the polycomb repressor complex 2 (PRC2). Also, TGFβ signaling promoted the expression of mir-100-let-7a-2-mir-125b-1 cluster host gene (MIR100HG), which enhanced TGFβ signaling and affected TGFβ-mediated cell cycle arrest. The MIR100HG-derived miRNAs let-7a-2-3p, miR125b-5p and miR-125b-1-3p, were also induced by TGFβ. In contrast, the long intergenic non-protein coding RNA 707 (LINC00707), was reduced in response to TGFβ and affected the expression of a group of genes related to inflammatory responses and interferon-γ (IFN-γ) signaling. We also report that TGFβ and BMP pathways are regulated by ADP-ribosylation of Smad proteins, the signaling mediators of these pathways. We observed that PARP1 and PARP2 attenuated, while PARG favored TGFβ signaling. Furthermore, PARP1 negatively regulated BMP signaling, by ADP-ribosylating Smad1 and Smad5, whereas PARG enhanced BMP signaling by de-ADP-ribosylating Smads. Collectively, we provide evidence that lncRNAs and ADP-ribosylating enzymes modulate TGFβ and BMP signaling pathways and propose models for their molecular mechanisms and functional roles