The accessory Vpr protein of human immunodeficiency virus type 1 (HIV-1) is a promiscuous activator of viral and cellular promoters. We report that Vpr enhances expression of the glucocorticoid receptor-induced mouse mammary tumor virus (MMTV) promoter and of the Tat-induced HIV-1 long terminal repeat promoter by directly binding to p300/CBP coactivators. In contrast, Vpr does not bind to p/CAF or to members of the p160 family of nuclear receptor coactivators, such as steroid receptor coactivator 1a and glucocorticoid receptor (GR)-interacting protein 1. Vpr forms a stable complex with p300 and also interacts with the ligand-bound glucocorticoid receptor in vivo. Mutation analysis showed that the C-terminal part of Vpr binds to the C-terminal portion of p300/CBP within amino acids 2045 to 2191. The same p300 region interacts with the p160 coactivators and with the adenovirus E1A protein. Accordingly, E1A competed for binding to p300 in vitro. Coexpression of E1A or of small fragments of p300 containing the Vpr binding site resulted in inhibition of Vpr's transcriptional effects. The C-terminal part of p300 containing the transactivating region is required for Vpr transactivation, whereas the histone acetyltransferase enzymatic region is dispensable. Vpr mutants that bind p300 but not the GR did not activate expression of the MMTV promoter and had dominant-negative effects. These results indicate that Vpr activates transcription by acting as an adapter linking transcription components and coactivators.

Vpr and selected mutants were used in a Saccharomyces cerevisiae two-hybrid screen to identify cellular interactors. We found Vpr interacted with 14-3-3 proteins, a family regulating a multitude of proteins in the cell. Vpr mutant R80A, which is inactive in cell cycle arrest, did not interact with 14-3-3. 14-3-3 proteins regulate the G ₂ /M transition by inactivating Cdc25C phosphatase via binding to the phosphorylated serine residue at position 216 of Cdc25C. 14-3-3 overexpression in human cells synergized with Vpr in the arrest of cell cycle. Vpr did not arrest efficiently cells not expressing 14-3-3σ. This indicated that a full complement of 14-3-3 proteins is necessary for optimal Vpr function on the cell cycle. Mutational analysis showed that the C-terminal portion of Vpr, known to harbor its cell cycle-arresting activity, bound directly to the C-terminal part of 14-3-3, outside of its phosphopeptide-binding pocket. Vpr expression shifted localization of the mutant Cdc25C S216A to the cytoplasm, indicating that Vpr promotes the association of 14-3-3 and Cdc25C, independently of the presence of serine 216. Immunoprecipitations of cell extracts indicated the presence of triple complexes (Vpr/14-3-3/Cdc25C). These results indicate that Vpr promotes cell cycle arrest at the G ₂ /M phase by facilitating association of 14-3-3 and Cdc25C independently of the latter's phosphorylation status.

The glucocorticoid receptor (GR) α interacts with the highly conserved 14-3-3 family proteins. The latter bind phosphorylated serine/threonine residues of “partner” molecules and influence many signal transduction events by altering their subcellular localization and/or protecting them from proteolysis. To examine the physiologic role of 14-3-3 on the glucocorticoid-signaling pathway, we studied the nucleocytoplasmic shuttling and transactivation properties of GRα in a cell line replete with or devoid of 14-3-3σ. We found that endogenous 14-3-3σ helped localize green fluorescent protein-fused GRα in the cytoplasm in the absence of ligand and potentiated its nuclear export after ligand withdrawal. 14-3-3σ also suppressed the transcriptional activity of GRα on a glucocorticoid-responsive promoter. Disruption of the classic nuclear export signal of 14-3-3σ inactivated its ability to influence the nucleocytoplasmic trafficking and transactivation activity of GRα, whereas introduction of a mutation inactivating the binding activity of 14-3-3σ to some of its partner proteins did not. 14-3-3σ bound the ligand-binding domain of GRα through its COOH-terminal portion, in a partially ligand-dependent fashion, while it did not interact with “ligand-binding domain” of GRβ at all. These results suggest that 14-3-3σ functions as a negative regulator in the glucocorticoid signaling pathway, possibly by shifting the subcellular localization/circulation of this receptor toward the cytoplasm through its nuclear export signal. Since 14-3-3 proteins play significant roles in numerous cellular activities, such as cell cycle progression, growth, differentiation, and apoptosis, these actions might indirectly influence the transcriptional activity of GRα. Conversely, through its 14-3-3 protein interactions, GRα may influence these processes.

To investigate whether anxiety and depression levels are associated with Heat Shock Protein 70 (HSP70) induction in the colon of patients with ulcerative colitis (UC).

Background/Aim: Recent knowledge implicates a differential expression of the insulin-like growth factor-I (IGF-I) mRNA splice variants (i.e., IGF-IEa, IGF-IEb and IGF-IEc) in cancerous tissues, implying possible specific roles of the encoded IGF-I protein isoforms in cancer biology. In particular, there is growing evidence that the IGF-IEc isoform may play a distinct biological role in various types of cancers. The present study investigated whether IGF-IEc expression is associated with a particular type of thyroid cancer. Materials and Methods: Formalin-fixed paraffin-embedded tissue specimens of different types of thyroid cancers from 92 patients were assessed for IGF-IEc expression by immunohistochemistry. In addition, thyroid cancer biopsies of different TNM staging histological types were evaluated for mRNA expression of the IGF-IEc transcript by real-time polymerase chain reaction (PCR). Results: From the total number of 92 samples, 2 were anaplastic, 10 medullary, 4 hyperplasias of C-cells, 11 follicular, 5 hurtle cell carcinomas, 2 poorly differentiated, 5 nodular hyperplasias, 1 lymphoma and 52 were papillary thyroid cancers. The age of cancer diagnosis or tumor size did not significantly affect the IGF-IEc expression. Among all types of cancers, IGF-IEc was expressed in papillary differentiated thyroid cancer. Its expression/localization was mainly cytoplasmic and significantly associated with TNM staging and the presence of muscular and capsule cancerous invasion (p<0.05). Similarly, a differential profile was revealed regarding the mRNA expression of the IGF-IEc transcript, that exhibited a higher expression in aggressive compared to the non-aggressive papillary cancers. Conclusion: IGF-IEc isoform expression in thyroid cancer is positively associated with more advanced stages of papillary thyroid cancer.