Human genomic clones that span the entire protein S expressed gene (PS alpha) and the 3' two-thirds of the protein S pseudogene (PS beta) have been isolated and characterized. The PS alpha gene is greater than 80 kilobases in length and contains 14 introns and 15 exons, as well as 6 repetitive "Alu" sequences. Exons I and XV contain 112 and 1139 bp 5' and 3' noncoding segments in addition to the amino and carboxyl termini, respectively. Exons I-VIII encode protein segments that are homologous to the vitamin K dependent clotting proteins and are bounded by introns whose position and type are identical with other members of this protein family. Exons IX-XV encode protein segments homologous to sex hormone binding globulin (SHBG) and are bounded by introns of identical type and position as in the SHBG gene. Genomic clones for the PS beta gene cover a distance of greater than 55 kilobases and contain segments corresponding to amino acids 46-635 of the mature protein and the 1.1-kb 3' noncoding region of the cDNA. The presence of multiple base changes in the coding portions of this gene, resulting in termination codons and frame shifts, suggests that it is a pseudogene. Comparison of DNA sequences for the two genes reveals 97% identity for coding and 3' noncoding, and 95.4% for intronic regions, suggesting divergence of the two genes is a relatively recent event.
Human RAD51 protein catalyzes DNA pairing and strand exchange reactions that are central to homologous recombination and homology-directed DNA repair. Successful recombination/repair requires the formation of a presynaptic filament of RAD51 on ssDNA. Mutations in BRCA2 and other proteins that control RAD51 activity are associated with human cancer. Here we describe a set of mutations associated with human breast tumors that occur in a common structural motif of RAD51. Tumor-associated D149N, R150Q and G151D mutations map to a Schellman loop motif located on the surface of the RecA homology domain of RAD51. All three variants are proficient in DNA strand exchange, but G151D is slightly more sensitive to salt than wild-type (WT). Both G151D and R150Q exhibit markedly lower catalytic efficiency for adenosine triphosphate hydrolysis compared to WT. All three mutations alter the physical properties of RAD51 nucleoprotein filaments, with G151D showing the most dramatic changes. G151D forms mixed nucleoprotein filaments with WT RAD51 that have intermediate properties compared to unmixed filaments. These findings raise the possibility that mutations in RAD51 itself may contribute to genome instability in tumor cells, either directly through changes in recombinase properties, or indirectly through changes in interactions with regulatory proteins.
The thyroid hormone receptor beta (TRb), a key regulator of cellular growth and differentiation, is frequently dysregulated in cancers. Diminished expression of TRb is noted in thyroid, breast, and other solid tumors and is correlated with more aggressive disease. Restoration of TRb levels decreased tumor growth supporting the concept that TRb could function as a tumor suppressor. Yet, the TRb tumor suppression transcriptome is not well delineated and the impact of TRb is unknown in aggressive anaplastic thyroid cancer (ATC). Here, we establish that restoration of TRb expression in the human ATC cell line SW1736 (SW-TRb) reduces the aggressive phenotype, decreases cancer stem cell populations and induces cell death in a T 3 -dependent manner. Transcriptomic analysis of SW-TRb cells via RNA sequencing revealed distinctive expression patterns induced by ligand-bound TRb and revealed novel molecular signaling pathways. Of note, liganded TRb repressed multiple nodes in the PI3K/AKT pathway, induced expression of thyroid differentiation markers, and promoted proapoptotic pathways. Our results further revealed the JAK1-STAT1 pathway as a novel, T 3 -mediated, antitumorigenic pathway that can be activated in additional ATC lines. These findings elucidate a TRb-driven tumor suppression transcriptomic signature, highlight unexplored therapeutic options for ATC, and support TRb activation as a promising therapeutic option in cancers.Implications: TRb-T 3 induced a less aggressive phenotype and tumor suppression program in anaplastic thyroid cancer cells revealing new potential therapeutic targets.
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