Evidence That IGF Binding Protein-5 Functions as a Ligand-Independent Transcriptional Regulator in Vascular Smooth Muscle Cells

Xu, Qijin; Li, Sheng‐Hua; Zhao, Yang; Maures, Travis J.; Yin, Ping; Duan, Cunming

doi:10.1161/01.res.0000124761.62846.df

Cited by 76 publications

(96 citation statements)

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“…It has also been reported that IGFBP-5 may interact with Four and a Half LIM protein 2 (FHL2) and retinoid X receptor, nuclear proteins known to be involved in transcriptional regulation (16,17). Recently, we have shown that 1) endogenous IGFBP-5 is localized in the nucleus of cultured porcine vascular smooth muscle cells; 2) several basic residues in the IGFBP-5 C-domain are necessary and sufficient for nuclear localization of the intact protein; and 3) the IGFBP-5 N-domain activates transcription independent of IGF (18). These findings suggest that IGFBP-5 is present in the nucleus and may affect gene expression independent of the IGF ligand.…”

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confidence: 99%

Several Acidic Amino Acids in the N-domain of Insulin-like Growth Factor-binding Protein-5 Are Important for Its Transactivation Activity

Zhao

Yin

Bach

et al. 2006

Journal of Biological Chemistry

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Insulin-like growth factor-binding protein (IGFBP)-5 is a secreted protein that binds to IGFs and modulates IGF actions. IGFBP-5 is also found in the nuclei of cultured cells and has transactivation activity.Here we report the nuclear localization of endogenous IGFBP-5 in mouse embryonic skeletal cells. Chromatin immunoprecipitation experiments indicated that IGFBP-5 interacts with the nuclear histone-DNA complex. Using a series of deletion mutants, the transactivation domain of IGFBP-5 was mapped to its N-terminal region. Intriguingly, the transactivation activity of IGFBP-5 is masked by negative regulatory elements located in the L-and C-domains. Among the other IGFBPs, the N-domains of IGFBP-2 and -3 also had strong transactivation activity, whereas those of IGFBP-1 and -6 had no activity. The IGFBP-4 N-domain had modest activity. Sequence analysis revealed several amino acids in the IGFBP-5 N-domain that are not present in IGFBP-1. The activities of mutants in which these residues were changed to the corresponding IGFBP-1 sequence were determined. Mutations that changed acidic residues to neutral residues (e.g. E8A, D11S, E12A, E30S/P31A, E43L, and E52A) or a polar to a basic residue (e.g. Q56R) significantly reduced transactivation activity. The E8A/D11S/E12A triple mutant and E52A/Q56R double mutants showed further reduced activity. The combinatory mutants had essentially no transactivation activity. Taken together, our results indicate that there are several conserved residues in the IGFBP-5 N-terminal region that are critical for transactivation and that IGFBP-2 and -3 also have strong transactivation activity in their N-domains.The insulin-like growth factor (IGF) 2 system, consisting of two ligands (IGF-I and -II), two receptors (the IGF-I receptor and IGF-II receptor), and six high affinity IGF-binding proteins (IGFBPs), converges on a conserved signaling pathway that plays fundamental roles in vertebrate development and physiology and is implicated in several human diseases (1). The bioavailability and bioactivity of IGFs are regulated by their interactions with various members of the IGFBP family. IGFBPs all have a highly cysteine-rich N-terminal (N)-domain, a cysteine-rich C-terminal (C)-domain, and a middle linker (L)-domain with no cysteine residues except in IGFBP-4. The N-and C-domains are highly conserved within the IGFBP family, whereas the L-domain varies both within the family and across species.Besides binding to IGF and modulating its actions, IGFBP-5 has been reported to regulate cell proliferation (2, 3), migration (4 -6), and apoptosis/survival (7-11) independent of IGF. Although the ligand-dependent actions of IGFBP-5 are attributed to its interactions with the IGF ligand and other proteins (1), the mechanistic basis of the ligand-independent actions of IGFBP-5 is not yet understood.Andress et al. (12) used IGFBP-5 affinity chromatography to purify a 420-kDa membrane protein from human osteoblast cells and proposed that it was an IGFBP-5 receptor. The same study reported that IGFBP-5 ...

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confidence: 99%

Several Acidic Amino Acids in the N-domain of Insulin-like Growth Factor-binding Protein-5 Are Important for Its Transactivation Activity

Zhao

Yin

Bach

et al. 2006

Journal of Biological Chemistry

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“…Loss of FLNa is associated with a loss of IGFBP-5-mediated induction of lamc1 transcription, thereby establishing the functional significance of these findings. Previous studies have indicated that IGF-1-independent effects of IGFBP-5 are mediated through intranuclear effects on transcription (9,13,18), yet details of those effects have not been elucidated. Similarly, intranuclear effects of FLNa that modulate effects of transcription factors on target genes have not been thoroughly defined.…”

Section: Discussionmentioning

confidence: 99%

“…This is the first demonstration of the interaction of IGFBP-5 with FLNa both in the cytosol and nucleus of IGFBP-5-treated cells. Additional studies are required to determine whether IGFBP-5 is directly mediating FLNa import into the nucleus or whether it has accessory effects on transcription (9,13).…”

Section: Igfbp-5 Induces Flna Binding and Nuclear Translocation Of Trmentioning

confidence: 99%

“…The C-terminal domain does not bind IGF-1, but it can influence the IGF-1 binding affinity (11). A highly basic domain in the C-terminal end of IGFBP-5 (amino acids 201-218) has a functional nuclear localization sequence (12), yet secretion and reuptake of protein and possibly proteolytic processing appears to be required for nuclear translocation (13). Cellular reuptake can occur by several mechanisms that are attributed to the C-terminal domain including uptake by a protein transduction domain (14), binding to transferrin with subsequent uptake by the transferrin receptor (15), a possible IGFBP-5 receptor (6), or interaction with the type V transforming growth factor ␤ receptor (16).…”

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“…It is possible that each of these uptake mechanisms lead to different biological responses. Studies to understand the intranuclear effects of IGFBP-5 have revealed a cryptic domain in the N-terminal portion of the molecule that can act as a transcriptional transactivator (13). Amaar et al (17) showed that IGFBP-5 [201][202][203][204][205][206][207][208][209][210][211][212][213][214][215][216][217][218] binds to the second and third LIM domains of FHL2, and they proposed that IGFBP-5 participates in transcriptional regulation through binding to this transcriptional co-activator.…”

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Insulin-like Growth Factor-binding Protein-5-induced Laminin γ1 Transcription Requires Filamin A

Abrass

Hansen

2010

Journal of Biological Chemistry

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Insulin-like growth factor-binding proteins (IGFBPs) 2 modulate IGF-1 action by preventing IGF-1 degradation and by modulating IGF-1 receptor binding (1, 2), yet among the six IGFBP that bind IGF-1, IGFBP-3 and IGFBP-5 exhibit IGFindependent effects (3-6). IGFBP-5 has important effects on cell proliferation, apoptosis, migration, and regulation of transcription (7-9), which have been shown to be relevant to understanding cell differentiation, senescence, and cancer (3). An N-terminal domain of IGFBP-5 contains the IGF-1-binding region and caveolin-binding sites (10). The C-terminal domain does not bind IGF-1, but it can influence the IGF-1 binding affinity (11). A highly basic domain in the C-terminal end of IGFBP-5 (amino acids 201-218) has a functional nuclear localization sequence (12), yet secretion and reuptake of protein and possibly proteolytic processing appears to be required for nuclear translocation (13). Cellular reuptake can occur by several mechanisms that are attributed to the C-terminal domain including uptake by a protein transduction domain (14), binding to transferrin with subsequent uptake by the transferrin receptor (15), a possible IGFBP-5 receptor (6), or interaction with the type V transforming growth factor ␤ receptor (16). It is possible that each of these uptake mechanisms lead to different biological responses. Studies to understand the intranuclear effects of IGFBP-5 have revealed a cryptic domain in the N-terminal portion of the molecule that can act as a transcriptional transactivator (13). Amaar et al. (17) showed that IGFBP-5 201-218 binds to the second and third LIM domains of FHL2, and they proposed that IGFBP-5 participates in transcriptional regulation through binding to this transcriptional co-activator. IGFBP-5 also influences gene transcription through interaction with the retinoic acid receptor-rexinoid receptor system (18). Less is known about IGFBP-5 gene targets and other steps involved in transcriptional control by IGFBP-5.Filamin A (FLNa) is a 280-kDa protein with an N-terminal actin-binding domain followed by 24 repeats that are interrupted by two hinge regions and a C terminus that is responsible for dimerization (19). The hinge regions allow FLNa to function as a molecular leaf spring, lending flexibility and stiffness to the actin filaments (19) when FLNa participates in connections between the intracellular domain of integrins and the cytoskeleton. The 24 Ig-like repeats serve as docking sites for a variety of proteins that regulate cellular responses to growth factors and perturbants of cell-matrix attachments. Thus far, more than 20 FLNa binding partners have been described, and more have been proposed (20). Sites that bind the intracellular domains of integrins (21), the potassium channel, androgen receptor (22), calcium sensing receptor (23), and prostate-specific antigen (24) are near the C terminus (repeats 16 -24). Signal transduction molecules, such as the Rho GTPases (Rho/ Rac/cdc42), RalA, and Smads, bind in repeats 17-23 (25-28). Other proteins can...

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Single‐Cell RNA Sequencing Uncovers Pathological Processes and Crucial Targets for Vascular Endothelial Injury in Diabetic Hearts

Zhang,

Cao,

Zhang

et al. 2024

Advanced Science

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Cardiovascular disease remains the leading cause of high mortality in individuals with diabetes mellitus. Endothelial injury is a major contributing factor for vascular dysfunction in diabetes. However, the precise mechanisms underlying endothelial cell injury and their heterogeneity in diabetes remains elusive. In this study, single‐cell sequencing is performed in heart tissues from leptin receptor knock‐out (db/db) diabetic mice at various pathological stages. Through cell cluster identification, differential gene analysis, intercellular communication analysis, pseudo time analysis, and transcription factor analysis, a novel mechanism of cardiac vascular endothelial damage in diabetes is identified. Specifically, a single‐cell transcription map of cardiac vascular endothelial cells is presented in db/db mice. Diverse cellular clusters are found to play vital roles under diabetes‐induced damage, highlighting crucial transcription factors involved in their regulation. In addition, the essential transcription factor Ets1 is found to protect against vascular endothelial injury in db/db mice. In summary, the work provides a comprehensive understanding of the development of diabetic cardiac vascular endothelial damage and the heterogeneity of the cells involved. These findings offer valuable insights into potential treatments and assessments of diabetic cardiovascular endothelial damage.

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Evidence That IGF Binding Protein-5 Functions as a Ligand-Independent Transcriptional Regulator in Vascular Smooth Muscle Cells

Cited by 76 publications

References 46 publications

Several Acidic Amino Acids in the N-domain of Insulin-like Growth Factor-binding Protein-5 Are Important for Its Transactivation Activity

Several Acidic Amino Acids in the N-domain of Insulin-like Growth Factor-binding Protein-5 Are Important for Its Transactivation Activity

Insulin-like Growth Factor-binding Protein-5-induced Laminin γ1 Transcription Requires Filamin A

Single‐Cell RNA Sequencing Uncovers Pathological Processes and Crucial Targets for Vascular Endothelial Injury in Diabetic Hearts

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