👤 Sonia B Sidhu

Lipoprotein (a) [Lp (a)] may confer pro-thrombotic potential, and high concentrations may be an independent risk for MI. This systematic review sought to investigate the association of Lp (a) levels with post-revascularization Major Adverse Cardiac Events (MACE) in patients with CAD, ACS, and DM. A systematic literature search for original investigations was performed using PubMed/MEDLINE, Embase, Scopus, and Google Scholar, searching for articles (meeting inclusion criteria) focusing on the relationship between Lp(a), DM, and PCI in patients with ACS, MI, or IHD and the impact on cardiovascular outcomes. The data was abstracted and descriptively summarized. The systematic review selected four relevant articles: 3 prospective Konishi et al., (2016); Silverio et al., (2022); and Li et al., (2023) and one retrospective (Takahashi et al., 2020). Total population: 4624, total males: 3719. Konishi et al. (2016) concluded that an elevated Lp(a) is an independent risk factor for cardiac death and/or ACS recurrence in diabetics undergoing PCI. The adjusted OR for cardiac death and ACS in the high Lp(a) group vs. the low Lp(a) group was 1.20 (CI 1.00-1.42), p = 0.04. Takahashi et al. (2020) showed that after adjusting for clinical covariates, high Lp(a) was independently associated with a higher frequency of MACE and poorer long-term outcomes compared to low Lp(a). The adjusted OR for the risk of MACE in patients with high Lp (a) vs. low Lp (a) was 1.83 (CI 1.16-2.95), p = 0.009. Silverio et al. (2022) showed that while there was an increased risk of recurrent MI in this patient population without DM, it was not confirmed in patients with DM. Compared with the lowest Lp (a) category, non-DM patients with very high Lp (a) >70 mg/dl vs. low Lp (a) showed a higher risk of recurrent MI and all-cause death; adjusted OR 2.839 (CI 1.382-5.832), p = 0.005. In diabetics, high Lp (a) vs. low Lp (a) = 1.115 (CI 0.405-3.071), p = 0.833. There is some evidence that Lp (a) levels are an independent risk factor for MACE in patients who underwent PCI for CAD. There is also some evidence that elevated Lp (a) levels are associated with a worse prognosis in patients with DM after PCI, but this association is not consistent in the literature. Further prospective multicenter studies are required in order to elucidate this association. Show less

Mahogunin ring finger 1 (MGRN1) is a membrane-tethered E3 ligase that fine-tunes signaling sensitivity by targeting surface receptors for ubiquitylation and degradation. Although MGRN1 is known to regulate the Hedgehog signaling effector Smoothened (SMO) via the transmembrane adapter multiple epidermal growth factor-like 8 (MEGF8), the broader scope of its regulatory network has been speculative. Here, we identify attractin (ATRN) and attractin-like 1 (ATRNL1) as additional transmembrane adapters that recruit MGRN1 and regulate cell surface receptor turnover. Through co-immunoprecipitation, we show that ATRN interacts with the RING domain of MGRN1. Functional assays suggest that ATRN and ATRNL1 work with MGRN1 to promote the ubiquitylation and degradation of the melanocortin receptors MC1R and MC4R, in a process analogous to its regulation of SMO. Loss of MGRN1 or ATRN leads to increased surface and ciliary localization of MC4R in fibroblasts and elevated MC1R levels in melanocytes, resulting in enhanced eumelanin production. These findings expand the known repertoire of MGRN1-regulated receptors and provide new insight into a shared mechanism by which membrane-tethered E3 ligases utilize transmembrane adapters to facilitate substrate receptor specificity. Show less

E3 ubiquitin ligases play a crucial role in modulating receptor stability and signaling at the cell surface, yet the mechanisms governing their substrate specificity remain incompletely understood. Mahogunin Ring Finger 1 (MGRN1) is a membrane-tethered E3 ligase that fine-tunes signaling sensitivity by targeting surface receptors for ubiquitination and degradation. Unlike cytosolic E3 ligases, membrane-tethered E3s require transmembrane adapters to selectively recognize and regulate surface receptors, yet few such ligases have been studied in detail. While MGRN1 is known to regulate the receptor Smoothened (SMO) within the Hedgehog pathway through its interaction with the transmembrane adapter Multiple Epidermal Growth Factor-like 8 (MEGF8), the broader scope of its regulatory network has been speculative. Here, we identify Attractin (ATRN) and Attractin-like 1 (ATRNL1) as additional transmembrane adapters that recruit MGRN1 and regulate cell surface receptor turnover. Through co-immunoprecipitation, we show that ATRN and ATRNL1 likely interact with the RING domain of MGRN1. Functional assays reveal that MGRN1 requires these transmembrane adapters to ubiquitinate and degrade the melanocortin receptors MC1R and MC4R, in a process analogous to its regulation of SMO. Loss of MGRN1 leads to increased surface and ciliary localization of MC4R in fibroblasts and elevated MC1R levels in melanocytes, with the latter resulting in enhanced eumelanin production. These findings expand the repertoire of MGRN1-regulated receptors and provide new insight into a shared mechanism by which membrane-tethered E3 ligases utilize transmembrane adapters to dictate substrate receptor specificity. By elucidating how MGRN1 selectively engages with surface receptors, this work establishes a broader framework for understanding how this unique class of E3 ligases fine-tunes receptor homeostasis and signaling output. Show less

Micro-RNAs are dysregulated in medullary thyroid carcinoma (MTC) and preliminary studies have shown that miRNAs may enact a therapeutic effect through changes in autophagic flux. Our aim was to study the in vitro effect of miR-9-3p on MTC cell viability, autophagy and to investigate the mRNA autophagy gene profile of sporadic versus hereditary MTC. The therapeutic role of miR-9-3p was investigated in vitro using human MTC cell lines (TT and MZ-CRC-1 cells), cell viability assays, and functional mechanism studies with a focus on cell cycle, apoptosis, and autophagy. Post-miR-9-3p transfection mRNA profiling of cell lines was performed using a customized, quantitative RT-PCR gene array card. This card was also run on clinical tumor samples (sporadic: n = 6; hereditary: n = 6) and correlated with clinical data. Mir-9-3p transfection resulted in reduced in vitro cell viability; an effect mediated through autophagy inhibition. This was accompanied by evidence of G2 arrest in the TT cell line and increased apoptosis in both cell lines. Atg5 was validated as a predicted miR-9-3p mRNA target in TT cells. Post-miR-9-3p transfection array studies showed a significant global decline in autophagy gene expression (most notably in PIK3C3, mTOR, and LAMP-1). Autophagy gene mRNAs were generally overexpressed in sporadic (vs. hereditary MTC) and Beclin-1 overexpression was shown to correlate with residual disease. Autophagy is a tumor cell survival mechanism in MTC that when disabled, is of therapeutic advantage. Beclin-1 expression may be a useful prognostic biomarker of aggressive disease. Show less

PDZ (PSD-95/Discs-large/ZO1) domains are interaction modules that typically bind to specific C-terminal sequences of partner proteins and assemble signaling complexes in multicellular organisms. We have analyzed the existing database of PDZ domain structures in the context of a specificity tree based on binding specificities defined by peptide-phage binding selections. We have identified 16 structures of PDZ domains in complex with high-affinity ligands and have elucidated four additional structures to assemble a structural database that covers most of the branches of the PDZ specificity tree. A detailed comparison of the structures reveals features that are responsible for the diverse specificities across the PDZ domain family. Specificity differences can be explained by differences in PDZ residues that are in contact with the peptide ligands, but these contacts involve both side-chain and main-chain interactions. Most PDZ domains bind peptides in a canonical conformation in which the ligand main chain adopts an extended β-strand conformation by interacting in an antiparallel fashion with a PDZ β-strand. However, a subset of PDZ domains bind peptides with a bent main-chain conformation and the specificities of these non-canonical domains could not be explained based on canonical structures. Our analysis provides a structural portrait of the PDZ domain family, which serves as a guide in understanding the structural basis for the diverse specificities across the family. Show less