Faculty Bibliography

Prolactinomas are the most frequently observed pituitary adenomas and most of them respond well to conventional treatment with dopamine agonists. However, a subset of prolactinomas fails to respond to such therapies and is considered as dopamine agonist-resistant prolactinomas (DARPs). New therapeutic approaches are necessary for these tumors. TGFbeta1 is a known inhibitor of lactotroph cell proliferation and prolactin secretion, and it partly mediates dopamine inhibitory action. TGFbeta1 is secreted to the extracellular matrix as an inactive latent complex, and its bioavailability is tightly regulated by different components of the TGFbeta1 system including latent binding proteins (LTBPs), local activators (Thrombospondin-1, matrix metalloproteases, integrins, among others), and TGFbeta receptors. Pituitary TGFbeta1 activity and the expression of different components of the TGFbeta1 system, are regulated by dopamine and estradiol. Prolactinomas (animal models and humans) present reduced TGFbeta1 activity as well as reduced expression of several components of the TGFbeta1 system. Therefore, restoration of TGFbeta1 inhibitory activity represents a novel therapeutic approach to bypass dopamine action in DARPs. The aim of this review is to summarize the large literature supporting TGFbeta1 important role as a local modulator of pituitary lactotroph function; as well to provide recent evidence of the restoration of TGFbeta1 activity as an effective treatment in experimental prolactinomas.

The molecular basis by which receptor tyrosine kinases (RTKs) recruit and phosphorylate Src Homology 2 (SH2) domain-containing substrates has remained elusive. We used X-ray crystallography, NMR spectroscopy, and cell-based assays to demonstrate that recruitment and phosphorylation of Phospholipase Cgamma (PLCgamma), a prototypical SH2 containing substrate, by FGF receptors (FGFR) entails formation of an allosteric 2:1 FGFR-PLCgamma complex. We show that the engagement of pTyr-binding pocket of the cSH2 domain of PLCgamma by the phosphorylated tail of an FGFR kinase induces a conformational change at the region past the cSH2 core domain encompassing Tyr-771 and Tyr-783 to facilitate the binding/phosphorylation of these tyrosines by another FGFR kinase in trans. Our data overturn the current paradigm that recruitment and phosphorylation of substrates are carried out by the same RTK monomer in cis and disclose an obligatory role for receptor dimerization in substrate phosphorylation in addition to its canonical role in kinase activation.

The tumor microenvironment (TME) represents a milieu that enables tumor cells to acquire the hallmarks of cancer. The TME is heterogeneous in composition and consists of cellular components, growth factors, proteases, and extracellular matrix. Concerted interactions between genetically altered tumor cells and genetically stable intratumoral stromal cells result in an "activated/reprogramed" stroma that promotes carcinogenesis by contributing to inflammation, immune suppression, therapeutic resistance, and generating premetastatic niches that support the initiation and establishment of distant metastasis. The lungs present a unique milieu in which tumors progress in collusion with the TME, as evidenced by regions of aberrant angiogenesis, acidosis and hypoxia. Inflammation plays an important role in the pathogenesis of lung cancer, and pulmonary disorders in lung cancer patients such as chronic obstructive pulmonary disease (COPD) and emphysema, constitute comorbid conditions and are independent risk factors for lung cancer. The TME also contributes to immune suppression, induces epithelial-to-mesenchymal transition (EMT) and diminishes efficacy of chemotherapies. Thus, the TME has begun to emerge as the "Achilles heel" of the disease, and constitutes an attractive target for anti-cancer therapy. Drugs targeting the components of the TME are making their way into clinical trials. Here, we will focus on recent advances and emerging concepts regarding the intriguing role of the TME in lung cancer progression, and discuss future directions in the context of novel diagnostic and therapeutic opportunities.

Connexin43 is the major component of gap junctions, an anatomical structure present in the cardiac intercalated disc that provides a low-resistance pathway for direct cell-to-cell passage of electrical charge. Recent studies have shown that in addition to its well-established function as an integral membrane protein that oligomerizes to form gap junctions, Cx43 plays other roles that are independent of channel (or perhaps even hemi-channel) formation. This article discusses non-canonical functions of Cx43. In particular, we focus on the role of Cx43 as a part of a protein interacting network, a connexome, where molecules classically defined as belonging to the mechanical junctions, the gap junctions and the sodium channel complex, multitask and work together to bring about excitability, electrical and mechanical coupling between cardiac cells. Overall, viewing Cx43 as a multi-functional protein, beyond gap junctions, opens a window to better understand the function of the intercalated disc and the pathological consequences that may result from changes in the abundance or localization of Cx43 in the intercalated disc subdomain.

Cardinal events in atherogenesis are the retention of apolipoprotein B-containing lipoproteins in the arterial wall and the reaction of macrophages to these particles. My laboratory has been interested in both the cell biological events producing apolipoprotein B-containing lipoproteins, as well as in the reversal of the damage they cause in the plaques formed in the arterial wall. In the 2013 George Lyman Duff Memorial Lecture, as summarized in this review, I covered 3 areas of my past, present, and future interests, namely, the regulation of hepatic very low density lipoprotein production by the degradation of apolipoprotein B100, the dynamic changes in macrophages in the regression of atherosclerosis, and the application of nanoparticles to both image and treat atherosclerotic plaques.

The cerebral vasculature provides the massive blood supply that the brain needs to grow and survive. By acquiring distinctive cellular and molecular characteristics it becomes the Blood Brain Barrier (BBB), a selectively permeable and protective interface between the brain and the peripheral circulation that maintains the extra-cellular milieu permissive for neuronal activity. Accordingly, there is great interest in uncovering the mechanisms that modulate the formation and differentiation of the brain vasculature. By performing a forward genetic screen in zebrafish we isolated no food for thought (nfty72), a recessive late-lethal mutant that lacks most of the intra-cerebral Central Arteries (CtAs), but not other brain blood vessels. We found that the cerebral vascularization deficit of nfty72 is caused by an inactivating lesion in reck (reversion-inducing-cysteine-rich protein with Kazal motifs or ST15; Suppressor of Tumorigenicity 15 protein), which encodes a membrane-anchored tumor suppressor glycoprotein. Our findings highlight Reck as a novel and pivotal modulator of the canonical Wnt signaling pathway that acts in endothelial cells to enable intra-cerebral vascularization and proper expression of molecular markers associated with BBB formation. Additional studies with cultured endothelial cells suggest that, in other contexts, Reck impacts vascular biology via the Vascular Endothelial Growth Factor (VEGF) cascade. Together, our findings have broad implications for both vascular and cancer biology.

Complex regulatory networks regulate stem cell behavior and contributions to tissue growth, repair, and homeostasis. A full understanding of the networks controlling stem cell self-renewal and differentiation, however, has not yet been realized. To systematically dissect these networks and identify their components, we performed an unbiased, transcriptome-wide in vivo RNAi screen in female Drosophila germline stem cells (GSCs). Based on characterized cellular defects, we classified 646 identified genes into phenotypic and functional groups and unveiled a comprehensive set of networks regulating GSC maintenance, survival, and differentiation. This analysis revealed an unexpected role for ribosomal assembly factors in controlling stem cell cytokinesis. Moreover, our data show that the transition from self-renewal to differentiation relies on enhanced ribosome biogenesis accompanied by increased protein synthesis. Collectively, these results detail the extensive genetic networks that control stem cell homeostasis and highlight the intricate regulation of protein synthesis during differentiation.

Many organisms accumulate a pool of germline stem cells during development that is maintained in later life. The dynamics of establishment, expansion and homeostatic maintenance of this pool are subject to both developmental and physiological influences including the availability of a suitable niche microenvironment, nutritional status, and age. Here, we investigated the dynamics of germline proliferation during stages of expansion and homeostasis, using the C. elegans germ line as a model. The vast majority of germ cells in the proliferative zone are in interphase stages of mitosis (G1, S, G2) rather than in the active mitotic (M) phase. We examined mitotic index and DNA content, comparing different life stages, mutants, and physiological conditions. We found that germ cells in larval stages cycle faster than in adult stages, but that this difference could not be attributed to sexual fate of the germ cells. We also found that larval germ cells exhibit a lower average DNA content compared to adult germ cells. We extended our analysis to consider the effects of distance from the niche and further found that the spatial pattern of DNA content differs between larval and adult stages in the wild type and among mutants in pathways that interfere with cell cycle progression, cell fate, or both. Finally, we characterized expansion of the proliferative pool of germ cells during adulthood, using a regeneration paradigm (ARD recovery) in which animals are starved and re-fed. We compared adult stage regeneration and larval stage expansion, and found that the adult germ line is capable of rapid accumulation but does not sustain a larval-level mitotic index nor does it recapitulate the larval pattern of DNA content. The regenerated germ line does not reach the number of proliferative zone nuclei seen in the continuously fed adult. Taken together, our results suggest that cell cycle dynamics are under multiple influences including distance from the niche, age and/or maturation of the germ line, nutrition and, possibly, latitude for physical expansion.

BACKGROUND: Systemic antibiotics are used widely to treat moderate to severe acne, but increasing antibiotic resistance makes appropriate use a priority. OBJECTIVE: We sought to determine the duration of systemic antibiotic use in patients with inflammatory/nodulocystic acne who eventually required isotretinoin. METHODS: We performed a retrospective, single-site chart review of patients with acne diagnostic codes evaluated January 1, 2005 to December 31, 2014, at a dermatology practice in an academic medical center. Included patients were prescribed isotretinoin during the study period and received 30 days or more of antibiotics. RESULTS: The average duration of antibiotic use was 331.3 days. In all, 21 patients (15.3%) were prescribed antibiotics for 3 months or less, 88 patients (64.2%) for 6 months or more, and 46 patients (33.6%) for 1 year or longer. Patients treated only at the study site had a mean duration of antibiotic treatment of 283.1 days whereas patients who also received antibiotics from another institution had a mean duration of 380.2 days. This difference approached statistical significance (P = .054). LIMITATIONS: This study was limited to a single center. CONCLUSION: Expert guidelines recommend responsible use of antibiotics in acne in light of emerging resistance. We found that patients who eventually received isotretinoin had extended exposure to antibiotics, exceeding recommendations. Early recognition of antibiotic failure and the need for isotretinoin can curtail antibiotic use.

Our previous research testified that XBP1S is a significant downstream mediator of BMP2 and is involved in BMP2-stimulated chondrocyte differentiation. Herein we report that ATF6 and ATF6a are expressed in growth plate chondrocytes. There are differentially induced during BMP2-triggered chondrocyte differentiation. This differential expression is probably resulted from the activation of the ATF6 gene by Runx2 and repression by Sox6 transcription factor. Runx2 and Sox6 combine with their respective binding elements of ATF6 gene. When overexpressed, ATF6 and ATF6a intensify chondrogenesis; our studies demonstrate that under the stimulation of ATF6 and ATF6a, chondrocytes tend to be hypertrophied and mineralized, a process leading to bone formation. Additionally, lowing expression of ATF6a using its specific siRNA suppresses chondrocyte differentiation. Moreover, ATF6a interacts with Runx2 and augments Runx2-mediated hypertrophied chondrocyte. Importantly, overexpression and knockdown of ATF6a in chondrocyte hypertrophy also lead to altered expressions of IHH and PTHrP. Taken together, these findings indicate that ATF6a favorably controls chondrogenesis and bone formation via a) acting as a co-factor of Runx2 and enhancing Runx2-incited hypertrophic chondrocyte differentiation, and b) affecting IHH/PTHrP signaling.