TRIM29 (tripartite motif-containing protein 29) is a TRIM family protein that has been implicated in breast, colorectal, and pancreatic cancers. However, its role in stratified squamous epithelial cells and tumors has not been elucidated.Here, we investigate the expression of TRIM29 in cutaneous head and neck squamous cell carcinomas (SCC) and its functions in the tumorigenesis of such cancers. TRIM29 expression was lower in malignant SCC lesions than in adjacent normal epithelial tissue or benign tumors. Lower expression of TRIM29 was associated with higher SCC invasiveness. Primary tumors of cutaneous SCC showed aberrant hypermethylation of TRIM29. Depletion of TRIM29 increased cancer cell migration and invasion; conversely, overexpression of TRIM29 suppressed these. Comprehensive proteomics and immuno-precipitation analyses identified keratins and keratin-interacting protein FAM83H as TRIM29 interactors. Knockdown of TRIM29 led to ectopic keratin localization of keratinocytes. In primary tumors, lower TRIM29 expression correlated with the altered expression of keratins. Our findings reveal an unexpected role for TRIM29 in regulating the distribution of keratins, as well as in the migration and invasion of SCC. They also suggest that the TRIM29-keratin axis could serve as a diagnostic and prognostic marker in stratified epithelial tumors and may provide a target for SCC therapeutics.Significance: These findings identify TRIM29 as a novel diagnostic and prognostic marker in stratified epithelial tissues. Cancer Res; 78(24); 6795-806. Ó2018 AACR.

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B cell lymphoma gene 2 (Bcl-2) family proteins are key regulators of programmed cell death and important targets for drug discovery. Pro-apoptotic and anti-apoptotic Bcl-2 family proteins reciprocally modulate their activities in large part through protein interactions involving a motif known as BH3 (Bcl-2 homology 3). Nur77 is an orphan member of the nuclear receptor family that lacks a BH3 domain but nevertheless binds certain anti-apoptotic Bcl-2 family proteins (Bcl-2, Bfl-1, and Bcl-B), modulating their effects on apoptosis and autophagy. We used a combination of NMR spectroscopy-based methods, mutagenesis, and functional studies to define the interaction site of a Nur77 peptide on anti-apoptotic Bcl-2 family proteins and reveal a novel interaction surface. Nur77 binds adjacent to the BH3 peptide-binding crevice, suggesting the possibility of crosstalk between these discrete binding sites. Mutagenesis of residues lining the identified interaction site on Bcl-B negated the interaction with Nur77 protein in cells and prevented Nur77-mediated modulation of apoptosis and autophagy. The findings establish a new protein interaction site with the potential to modulate the apoptosis and autophagy mechanisms governed by Bcl-2 family proteins.In metazoans, Bcl-2 5 family proteins regulate several cellular processes, most prominently apoptosis (programmed cell death) and also autophagy (1, 2). Based on primary amino acid sequence similarity, members of the Bcl-2 protein family share at least one of four modular components, termed Bcl-2 homology (BH) domains. Of these, BH3 has an amphipathic ␣-helical structure and plays a pivotal role in both the activation of proapoptotic and the suppression of anti-apoptotic members of the family. For example, the BH3 domains of Bim, Bid, and Puma trigger conformational changes in the executioners Bax and Bak, leading to their oligomerization and permeation of the outer mitochondrial membrane. Downstream consequences of Bax and Bak activation include release of cytochrome c and, ultimately, the activation of caspase-9 and other cell death proteases. Conversely, the BH3 domains of these and other BH3-carrying proteins bind anti-apoptotic Bcl-2 family proteins and inhibit their ability to prevent Bax/Bak oligomerization in the outer mitochondrial membrane.The BH3 domain of pro-apoptotic proteins operates analogous to a ligand to interact with a predominantly hydrophobic receptor-like binding crevice on the surfaces of anti-apoptotic Bcl-2 family proteins. In addition to regulating apoptosis, the BH3-binding pocket on anti-apoptotic Bcl-2 family proteins has been reported to bind a BH3-like domain in the autophagy protein Beclin-1, and this interaction has been shown to play an important role in regulating autophagy (3). Prior work has dissected the binding affinity of various BH3 peptides (ligands) to anti-apoptotic Bcl-2 proteins (receptors), and three-dimensional structural data are available for several of these pairs (reviewed in Ref. 4).Targeting the BH3-binding cleft of anti-apo...