Inter-Tissue and Intra-Tissue Co-Expression Networks in Human Metabolism: Morphological Evaluation of the Link Between Transcription Factors ERβ and NFAT in Morbid Obesity

BACKGROUND

Estrogen receptor β (ERβ) plays an important role in human metabolism and some of its metabolic actions are mediated by a positive "cross-talk" with Nuclear Factor of Activated T cells (NFAT) and the key metabolic transcriptional coregulator Transcriptional Intermediary Factor 2 (TIF2).

INTRODUCTION

Our study is an "in situ" morphological evaluation of the communication between ERβ, NFAT and TIF2 in morbid obesity. Potential correlations with clinicopathological parameters and with the presence of diabetes and non-alcoholic fatty liver disease (NAFLD) were also explored. The aim of the present study was to determine the role of ERβ and NFAT in the underlying pathophysiology of obesity and related comorbidities. We have investigated the expression of specific proteins using immunochemistry methodologies.

METHODS

Our population consists of 50 morbidly obese patients undergoing planned bariatric surgery, during which biopsies were taken from visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), skeletal muscle (SM), extramyocellular adipose tissue (EMAT) and liver and the differential protein expression was evaluated by immunohistochemistry.

RESULTS

We demonstrated an extensive intra- and inter-tissue co-expression network, which confirms the tissue-specific and integral role of each one of the investigated proteins in morbid obesity. Moreover, a beneficial role of ERβ and NFATc1 against NAFLD is implicated, whereas the distinct roles of TIF2 still remain an enigma.

CONCLUSION

We believe that our findings will shed light on the complex underlying mechanisms and that the investigated biomarkers could represent future targets for the prevention and therapy of obesity and its comorbidities.

Unstable Protein Purification Through the Formation of Stable Complexes

Purification of proteins containing disordered regions and participating in transient complexes is often challenging because of the small amounts available after purification, their heterogeneity, instability, and/or poor solubility. To circumvent these difficulties, we set up a methodology that enables the production of stable complexes in large amounts for structural and functional studies. In this chapter, we describe the methodology used to establish the best cell culture conditions and buffer compositions to optimize soluble protein production and their stabilization through protein complex formation. Two examples of challenging protein families are described, namely, the human steroid nuclear receptors and the HIV-1 pre-integration complexes.

Cyclin C interacts with steroid receptor coactivator 2 and upregulates cell cycle genes in MCF-7 cells

Steroid receptor coactivator 2 (SRC-2) is a coactivator that regulates nuclear receptor activity. We previously reported that SRC-2 protein is degraded through the action of cAMP-dependent protein kinase A (PKA) and cAMP response element binding protein (CREB). In the study presented here, we aimed to identify proteins that interact with and thereby regulate SRC-2. We isolated cyclin C (CCNC) as an interacting partner with the SRC-2 degradation domain aa 347-758 in a yeast two-hybrid assay and confirmed direct interaction in an in vitro assay. The protein level of SRC-2 was increased with CCNC overexpression in COS-1 cells and decreased with CCNC silencing in COS-1 and MCF-7 cells. In a pulse-chase assay, we further show that silencing of CCNC resulted in a different SRC-2 degradation pattern during the first 6 h after the pulse. Finally, we provide evidence that CCNC regulates expression of cell cycle genes upregulated by SRC-2. In conclusion, our results suggest that CCNC temporarily protects SRC-2 against degradation and this event is involved in the transcriptional regulation of SRC-2 cell cycle target genes.

Structural and evolutionary analysis of the co-activator binding domain in vertebrate progesterone receptors

Biochemical studies show that binding of co-activators to the progesterone receptor [PR] is an important mechanism for regulating of PR-mediated gene transcription. Unfortunately, unlike other steroid receptors, the PR has not been crystalized with a co-activator. Fortunately, the PR has strong structural similarity to the mineralocorticoid receptor [MR] and glucocorticoid receptor [GR], which have been crystalized with co-activators. This similarity allowed us to construct 3D models of the PR with steroid co-activator 1-Box 4 [SRC1-4] and transcriptional intermediary factor 2-Box 3 [TIF2-3], which were extracted from the crystal structures of human MR and GR, respectively. Comparisons of 3D models of human PR with SRC1-4 and TIF2-3 and human MR with SRC1-4 and GR with TIF2-3 identified some unique interactions between the PR and SRC1-4 and TIF2-3. An evolutionary analysis of the sequence of the co-activator binding groove in human PR found strong conservation in terrestrial vertebrates. However, there are some differences between human PR and the PRs in lamprey, shark and fishes. These differences among the PRs and between the PR, MR and GR may have contributed to the evolution of specificity for progestins, mineralocorticoids and glucocorticoids in vertebrates.

PELP1: a review of PELP1 interactions, signaling, and biology

Proline, glutamic acid, and leucine rich protein 1 (PELP1) is a large multi-domain protein that has been shown to modulate an increasing number of pathways and biological processes. The first reports describing the cloning and characterization of PELP1 showed that it was an estrogen receptor coactivator. PELP1 has now been shown to be a coregulator for a growing number of transcription factors. Furthermore, recent reports have shown that PELP1 is a member of chromatin remodeling complexes. In addition to PELP1 nuclear functions, it has been shown to have cytoplasmic signaling functions as well. In the cytoplasm PELP1 acts as a scaffold molecule and mediates rapid signaling from growth factor and hormone receptors. PELP1 signaling ultimately plays a role in cancer biology by increasing proliferation and metastasis, among other cellular processes. Here we will review (1) the cloning and characterization of PELP1 expression, (2) interacting proteins, (3) PELP1 signaling, and (4) PELP1-mediated biology.

Nuclear EGFR as a molecular target in cancer

The epidermal growth factor receptor (EGFR) has been one of the most targeted receptors in the field of oncology. While anti-EGFR inhibitors have demonstrated clinical success in specific cancers, most patients demonstrate either intrinsic or acquired resistance within one year of treatment. Many mechanisms of resistance to EGFR inhibitors have been identified, one of these being attributed to alternatively localized EGFR from the cell membrane into the cell's nucleus. Inside the nucleus, EGFR functions as a co-transcription factor for several genes involved in cell proliferation and angiogenesis, and as a tyrosine kinase to activate and stabilize proliferating cell nuclear antigen and DNA dependent protein kinase. Nuclear localized EGFR is highly associated with disease progression, worse overall survival in numerous cancers, and enhanced resistance to radiation, chemotherapy, and the anti-EGFR therapies gefitinib and cetuximab. In this review the current knowledge of how nuclear EGFR enhances resistance to cancer therapeutics is discussed, in addition to highlighting ways to target nuclear EGFR as an anti-cancer strategy in the future.