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The mutated in colorectal cancer ( MCC) is a multifunctional gene showing loss of expression in colorectal and liver cancers. MCC mutations can drive colon carcinogenesis in the mouse and in vitro experiments suggest that loss of MCC function promotes cancer through several important cellular pathways. In particular, the MCC protein is known to regulate beta-catenin (β-cat) signaling, but the mechanism is poorly understood. Here we show that the β-cat repressor function of MCC is strongly impaired by the presence of a disease-associated mutation. We also identify deleted in breast cancer 1 (DBC1) as a new MCC interacting partner and regulator of β-cat signaling. RNA interference experiments show that DBC1 promotes β-cat transcriptional activity and that the presence of DBC1 is required for MCC-mediated β-cat repression. In contrast to all other DBC1 interacting partners, MCC does not interact through the DBC1 Leucine Zipper domain but with a glutamic-acid rich region located between the Nudix and EF-hand domains. Furthermore, MCC overexpression relocalizes DBC1 from the nucleus to the cytoplasm and reduces β-cat K49 acetylation. Treatment of cells with the SIRT1 inhibitor Nicotinamide reverses MCC-induced deacetylation of β-cat K49. These data suggest that the cytoplasmic MCC-DBC1 interaction sequesters DBC1 away from the nucleus, thereby removing a brake on DBC1 nuclear targets, such as SIRT1. This study provides new mechanistic insights into the DBC1-MCC axis as a new APC independent β-cat inhibitory pathway. [ABSTRACT FROM AUTHOR]

Abstract: The functions of Src family kinases are tightly regulated through Src homology (SH) domain-mediated protein–protein interactions. We previously reported the biophysical characteristics of the apoptosis-linked gene 2-interacting protein X (Alix) in complex with the haemopoietic cell kinase (Hck) SH3 domain. In the current study, we have combined ITC, NMR, SAXS and molecular modeling to determine a 3D model of the complex. We demonstrate that Hck SH3 recognizes an extended linear proline-rich region of Alix. This particular binding mode enables Hck SH3 to sense a specific non-canonical residue situated in the SH3 RT-loop of the kinase. The resulting model helps clarify the mechanistic insights of Alix–Hck interaction. Structured summary of protein interactions: Hck physically interacts with SAM68 by two hybrid ( View interaction ) FynR96I physically interacts with Alix by two hybrid ( View interaction ) Hck binds to Alix by pull down ( View interaction ) Fyn physically interacts with SAM68 by two hybrid ( View interaction ) Hck and Alix bind by nuclear magnetic resonance ( View interaction ) FynR96I and Alix bind by isothermal titration calorimetry (View Interaction: 1 , 2 ) FynR96I and Alix bind by nuclear magnetic resonance ( View interaction ) FynR96I binds to Alix by pull down ( View interaction ) Hck physically interacts with Alix by two hybrid ( View interaction ) FynR96I and Alix bind by x ray scattering ( View interaction ) Hck physically interacts with NEF by two hybrid ( View interaction ) FynR96I physically interacts with NEF by two hybrid ( View interaction ) [Copyright &y& Elsevier]

Cell-to-cell contact between peripheral blood lymphocytes and transfected human colonic carcinoma cell line HT29 activates transcription of the long terminal repeats (LTR) of human immunodeficiency virus. HIV-1 LTR transcription is controlled by a complex array of virus-encoded and cellular proteins. Using various constructs expressing a lacZ reporter gene under the control of the intact or three deleted forms of HIV-1 LTR, we obtained evidence that the κB regulatory elements located in the U3 region are involved in cell-to-cell activation of HIV-1 LTR. Cell-to-cell contact activates in vitro binding of the nuclear factor κB (NF-κB) p50/p65 heterodimer to an HIV-1 κB oligonucleotide. Cell-to-cell conflict activation of NF-κB was only partially inhibited by 100 μM pyrrolidine dithiocarbamate and was not correlated with a significant decrease of cellular inhibitor κBa. NF-κB nuclear activation was not detectable before 1 h after cell contact and was dependent on protein synthesis. [ABSTRACT FROM AUTHOR]