Faculty Bibliography

ADAMTS-18 is a member of a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) family of proteases, which are known to play important roles in development, angiogenesis and coagulation; dysregulation and mutation of these enzymes have been implicated in many disease processes, such as inflammation, cancer, arthritis and atherosclerosis. Mutations of ADAMTS-18 have been linked to abnormal early eye development and reduced bone mineral density. In this review, we briefly summarize the structural organization and the expression of ADAMTS-18. We will also focus on the emerging role of ADAMTS-18 in several pathophysiological conditions which include: hematological diseases, tumorgenesis, osteogenesis, eye-related diseases, central nervous system disorders, and last but not least a research perspective of ADAMTS-18 and its potential as a promising diagnostic and therapeutic target.

The ATP-binding cassette transporter A1 (ABCA1) is a major regulator of cellular cholesterol efflux and plasma high-density lipoprotein (HDL) biogenesis. Even though the transcriptional activation of ABCA1 is well established, the post-transcriptional regulation of ABCA1 expression is poorly understood. Here, we investigate the potential contribution of the Ribonucleoprotein-binding protein (RIP), HuR on the post-transcriptional regulation of ABCA1 expression. RNA immunoprecipitation assays demonstrate a direct interaction between HuR and ABCA1 mRNA. We found that HuR binds to the 3-untranslated region (UTR) region of ABCA1 and increases ABCA1 translation, while HuR silencing reduces ABCA1 expression and cholesterol efflux to ApoA1 in human hepatic (Huh-7) and monocytic (THP-1) cells. Interestingly, cellular cholesterol levels regulate the expression, intracellular localization and interaction between HuR and ABCA1 mRNA. Finally, we found that HuR expression was significantly increased in macrophages from human atherosclerotic plaques, suggesting an important role for this RBP in controlling macrophage cholesterol metabolism in vivo. In summary, we have identified HuR as a novel post-transcriptional regulator of ABCA1 expression and cellular cholesterol homeostasis, thereby opening new avenues for increasing cholesterol efflux from atherosclerotic foam macrophages and raising circulating HDL cholesterol levels.

We previously reported that transcription factor XBP1S binds to RUNX2 and enhances chondrocyte hypertrophy through acting as a cofactor of RUNX2. Herein, we report that XBP1S is a key downstream molecule of BMP2 and is required for BMP2-mediated chondrocyte differentiation. XBP1S is up-regulated during chondrocyte differentiation and demonstrates the temporal and spatial expression pattern during skeletal development. XBP1S stimulates chondrocyte differentiation from mesenchymal stem cells in vitro and endochondral ossification ex vivo. In addition, XBP1S activates granulin-epithelin precursor (GEP), a growth factor known to stimulate chondrogenesis, and endogenous GEP is required, at least in part, for XBP1S-stimulated chondrocyte hypertrophy, mineralization and endochondral bone formation. Furthermore, XBP1S enhances GEP-stimulated chondrogenesis and endochondral bone formation. Collectively, these findings demonstrate that XBP1S, a BMP2-inducible transcription factor, positively regulates endochondral bone formation by activating GEP chondrogenic growth factor.

OBJECTIVE: To determine the role of ANK/Myb-binding protein 1a (MYBBP1a) and sphingosine kinase 1 (SPHK1) interactions in catabolic events of articular chondrocytes. METHOD: ANK/MYBBP1a and SPHK1 interactions were identified using yeast two-hybrid screening and co-immunoprecipitation. To determine the role of these interactions in catabolic events of articular chondrocytes, ank/ank and wild type mouse chondrocytes transfected with full-length or mutant ank expression vectors or femoral heads were treated with interleukin-1beta (IL-1beta) in the absence or presence of SPHK inhibitor. Catabolic marker mRNA levels were analyzed by real time PCR; proteoglycan loss using safranin O staining and MMP-13 immunostaining were determined in femoral head explants; NF-kappaB activity was determined by transfecting chondrocytes with a NF-kappaB-specific luciferase reporter and analyzing nuclear translocation of p65 by immunoblotting; MYBBP1a nuclear or cytoplasmic amounts were determined by immunohistochemistry and immunoblotting. RESULTS: The ANK N-terminal region interacted with SPHK1, whereas a cytoplasmic C-terminal loop interacted with MYBBP1a. Lack of ANK/MYBBP1a and SPHK1 interactions in ank/ank chondrocytes resulted in increased MYBBP1a nuclear amounts and decreased SPHK1 activity, and consequently decreased NF-kappaB activity, catabolic marker mRNA levels, proteoglycan loss, and MMP-13 immunostaining in IL-1beta-treated articular chondrocytes or femoral heads. Transfection with full-length ank expression vector reduced nuclear MYBBP1a amounts and fully restored SPHK and NF-kappaB activities in IL-1beta-treated ank/ank chondrocytes, whereas transfection with P5L or F376del mutant ank reduced nuclear MYBBP1a or increased SPHK activity, respectively, and consequently either transfection only partially restored NF-kappaB activity. CONCLUSION: ANK/MYBBP1a and SPHK1 interactions stimulate catabolic events in IL-1beta-mediated cartilage degradation.

The SLC13 transporter family, whose members play key physiological roles in the regulation of fatty acid synthesis, adiposity, insulin resistance, and other processes, catalyzes the transport of Krebs cycle intermediates and sulfate across the plasma membrane of mammalian cells. SLC13 transporters are part of the divalent anion:Na(+) symporter (DASS) family that includes several well-characterized bacterial members. Despite sharing significant sequence similarity, the functional characteristics of DASS family members differ with regard to their substrate and coupling ion dependence. The publication of a high resolution structure of dimer VcINDY, a bacterial DASS family member, provides crucial structural insight into this transporter family. However, marrying this structural insight to the current functional understanding of this family also demands a comprehensive analysis of the transporter's functional properties. To this end, we purified VcINDY, reconstituted it into liposomes, and determined its basic functional characteristics. Our data demonstrate that VcINDY is a high affinity, Na(+)-dependent transporter with a preference for C4- and C5-dicarboxylates. Transport of the model substrate, succinate, is highly pH dependent, consistent with VcINDY strongly preferring the substrate's dianionic form. VcINDY transport is electrogenic with succinate coupled to the transport of three or more Na(+) ions. In contrast to succinate, citrate, bound in the VcINDY crystal structure (in an inward-facing conformation), seems to interact only weakly with the transporter in vitro. These transport properties together provide a functional framework for future experimental and computational examinations of the VcINDY transport mechanism.

SUMMARY: The recognition that the tumor microenvironment contributes to tumor survival, growth, and response to therapy provides the rationale for considering it a therapeutic target. The article by Alspach and colleagues in this issue provides evidence that p38MAPK acts posttranscriptionally to promote the tumor-permissive secretory phenotype of both cancer-associated and senescent fibroblasts, and that p38MAPK inhibitors already in clinical trials have significant therapeutic potential. Cancer Discov; 4(6); 637-9. (c)2014 AACR. See related article by Alspach et al., p. 716.

Human endogenous retroviruses (HERVs) are viruses that have colonized the germ line and spread through vertical passage. Only the more recently acquired HERVs, such as the HERV-K (HML-2) group, maintain coding open reading frames. Expression of HERV-Ks has been linked to different pathological conditions, including HIV infection, but our knowledge on which specific HERV-Ks are expressed in primary lymphocytes currently is very limited. To identify the most expressed HERV-Ks in an unbiased manner, we analyzed their expression patterns in peripheral blood lymphocytes using Pacific Biosciences (PacBio) single-molecule real-time (SMRT) sequencing. We observe that three HERV-Ks (KII, K102, and K18) constitute over 90% of the total HERV-K expression in primary human lymphocytes of five different donors. We also show experimentally that two of these HERV-K env sequences (K18 and K102) retain their ability to produce full-length and posttranslationally processed envelope proteins in cell culture. We show that HERV-K18 Env can be incorporated into HIV-1 but not simian immunodeficiency virus (SIV) particles. Moreover, HERV-K18 Env incorporation into HIV-1 virions is dependent on HIV-1 matrix. Taken together, we generated high-resolution HERV-K expression profiles specific for activated human lymphocytes. We found that one of the most abundantly expressed HERV-K envelopes not only makes a full-length protein but also specifically interacts with HIV-1. Our findings raise the possibility that these endogenous retroviral Env proteins could directly influence HIV-1 replication. IMPORTANCE: Here, we report the HERV-K expression profile of primary lymphocytes from 5 different healthy donors. We used a novel deep-sequencing technology (PacBio SMRT) that produces the long reads necessary to discriminate the complexity of HERV-K expression. We find that primary lymphocytes express up to 32 different HERV-K envelopes, and that at least two of the most expressed Env proteins retain their ability to make a protein. Importantly, one of them, the envelope glycoprotein of HERV-K18, is incorporated into HIV-1 in an HIV matrix-specific fashion. The ramifications of such interactions are discussed, as the possibility of HIV-1 target tissue broadening and immune evasion are considered.