Biomedical subjects

Mukesh K Jain

Publications and source records attributed to Mukesh K Jain.

23 records · Page 2Linked to original sources

PubMed2004

Integrin engagement regulates monocyte differentiation through the forkhead transcription factor Foxp1.

The precise signals responsible for differentiation of blood-borne monocytes into tissue macrophages are incompletely defined. "Outside-in" signaling by integrins has been implicated in modulation of gene expression that affects cellular differentiation. Herein, using differential display PCR, we have cloned an 85-kDa forkhead transcription factor (termed Mac-1-regulated forkhead [MFH] and found subsequently to be identical to Foxp1) that is downregulated in beta(2)-integrin Mac-1-clustered compared with Mac-1-nonclustered monocytic THP-1 cells. MFH/Foxp1 is expressed in untreated HL60 cells, and its expression was markedly reduced during phorbol ester-induced monocyte differentiation, but not retinoic acid-induced granulocyte differentiation. Overexpression of MFH/Foxp1 markedly attenuated phorbol ester-induced expression of c-fms, which encodes the M-CSF receptor and is obligatory for macrophage differentiation. This was accompanied by decreased CD11b expression, cell adhesiveness, and phagocytosis. Using electromobility shift and reporter assays, we have established that MFH/Foxp1 binds to previously uncharacterized sites within the c-fms promoter and functions as a transcriptional repressor. Deficiency of Mac-1 is associated with altered regulation of MFH/Foxp1 and monocyte maturation in vivo. Taken together, these observations suggest that Mac-1 engagement orchestrates monocyte-differentiation signals by regulating the expression of the forkhead transcription repressor MFH/Foxp1. This represents a new pathway for integrin-dependent modulation of gene expression and control of cellular differentiation.

Amino Acid Sequence↗

PubMed2002

The Krüppel-like factor KLF2 inhibits peroxisome proliferator-activated receptor-gamma expression and adipogenesis.

Obesity is an important public health problem associated with a number of disease states such as diabetes and arteriosclerosis. As such, an understanding of the mechanisms governing adipose tissue differentiation and function is of considerable importance. We recently reported that the Krüppel-like zinc finger transcription factor KLF15 can induce adipocyte maturation and GLUT4 expression. In this study, we identify that a second family member, KLF2/Lung Krüppel-like factor (LKLF), as a negative regulator of adipocyte differentiation. KLF2 is highly expressed in adipose tissue, and studies in cell lines and primary cells demonstrate that KLF2 is expressed in preadipocytes but not mature adipocytes. Constitutive overexpression of KLF2 but not KLF15 potently inhibits peroxisome proliferator-activated receptor-gamma (PPARgamma) expression with no effect on the upstream regulators C/EBPbeta and C/EBPdelta. However, the expression of C/EBPalpha and SREBP1c/ADD1 (adipocyte determination and differentiation factor-1/sterol regulatory element-binding protein-1), two factors that feedback in a positive manner to enhance PPARgamma function, was also markedly reduced. In addition, transient transfection studies show that KLF2 directly inhibits PPARgamma2 promoter activity (70% inhibition; p < 0.001). Using a combination of promoter mutational analysis and gel mobility shift assays, we have identified a binding site within the PPARgamma2 promoter, which mediates this inhibitory effect. These data identify a novel role for KLF2 as a negative regulator of adipogenesis.

Adipocytes↗

PubMed2002

Regulation of smooth muscle cell differentiation by AT-rich interaction domain transcription factors Mrf2alpha and Mrf2beta.

Despite the importance of vascular smooth muscle cells in the regulation of blood vessel function, the molecular mechanisms governing their development and differentiation remain poorly understood. Using an in vitro system whereby a pluripotent neural crest cell line (MONC-1) can be induced to differentiate into smooth muscle cells, we isolated a cDNA fragment that was robustly induced during this differentiation process. Sequence analysis revealed high homology to a partial cDNA termed modulator recognition factor 2 (Mrf2). Because the full-length cDNA has not been reported, we cloned the full-length Mrf2 cDNA by cDNA library screening and 5' rapid amplification of cDNA ends and identified two isoforms of Mrf2 (alpha [3.0 kb] and beta [3.7 kb]) that differ in the N-terminus but share the DNA-binding domain. Protein homology analysis suggests that Mrf2 is a member of the AT-rich interaction domain family of transcription factors, which are known to be critically involved in the regulation of development and cellular differentiation. Mrf2alpha and Mrf2beta are highly induced during in vitro differentiation of MONC-1 cells into smooth muscle cells, and Mrf2alpha is expressed in adult mouse cardiac and vascular tissues. To define the function of Mrf2, we overexpressed both isoforms in 3T3 fibroblast cells and observed an induction of smooth muscle marker genes, including smooth muscle alpha-actin and smooth muscle 22alpha. Furthermore, Mrf2alpha and Mrf2beta retarded cellular proliferation. These data implicate Mrf2 as a novel regulator of smooth muscle cell differentiation and proliferation.

3T3 Cells↗

PubMed2002

The Krüppel-like factor KLF15 regulates the insulin-sensitive glucose transporter GLUT4.

Resistance to the stimulatory effects of insulin on glucose utilization is a key feature of type 2 diabetes, obesity, and the metabolic syndrome. Recent studies suggest that insulin resistance is primarily caused by a defect in glucose transport. GLUT4 is the main insulin-responsive glucose transporter and is expressed predominantly in muscle and adipose tissues. Whereas GLUT4 has been shown to play a critical role in maintaining systemic glucose homeostasis, the mechanisms regulating its expression are incompletely understood. We have cloned the murine homologue of KLF15, a member of the Krüppel-like family of transcription factors. KLF15 is highly expressed in adipocytes and myocytes in vivo and is induced when 3T3-L1 preadipocytes are differentiated into adipocytes. Overexpression of KLF15 in adipose and muscle cell lines potently induces GLUT4 expression. This effect is specific to KLF15 as overexpression of two other Krüppel-like factors, KLF2/LKLF and KLF4/GKLF, did not induce GLUT4 expression. Both basal (3.3-fold, p < 0.001) and insulin-stimulated (2.4-fold, p < 0.00001) glucose uptake are increased in KLF15-overexpressing adipocytes. In co-transfection assays, KLF15 and MEF2A, a known activator of GLUT4, synergistically activates the GLUT4 promoter. Promoter deletion and mutational analyses provide evidence that this activity requires an intact KLF15-binding site proximal to the MEF2A site. Finally, co-immunoprecipitation assays show that KLF15 specifically interacts with MEF2A. These studies indicate that KLF15 is an important regulator of GLUT4 in both adipose and muscle tissues.

3T3 Cells↗

PubMed2002

Macrophage-restricted and interferon gamma-inducible expression of the allograft inflammatory factor-1 gene requires Pu.1.

Expression of allograft inflammatory factor-1 (Aif-1), a 17-kDa protein bearing an EF-hand Ca(2+) binding motif, increases markedly in monocytes and macrophages participating in allo- and autoimmune reactions, including the perivascular inflammation in transplanted hearts, microglial infiltrates in experimental autoimmune neuritis, and the inflamed pancreas of prediabetic BB rats. To investigate the mechanism of this regulation, we isolated the mouse aif-1 gene and determined its genomic organization. The gene has six exons distributed over 1.6 kilobases, an interferon gamma-inducible DNase I-hypersensitive site near -900, and flanking sequences on either side predicted to associate with nuclear matrix. Reporter gene analyses identified sequences between -902 and -789, including consensus Ets and interferon regulatory factor elements, required for macrophage-specific and interferon gamma-inducible transcriptional activity. Pu.1 bound to the Ets site in electromobility shift assay and forced expression of Pu.1 activated the aif-1 promoter in 3T3 fibroblasts, in which it is normally inactive. However, the transcriptional activity of a concatamer of the Ets site alone did not increase with interferon gamma treatment. Cooperation between Pu.1 and proteins binding to the interferon regulatory factor element appears to be necessary for both macrophage-specific and interferon gamma-inducible expression of the aif-1 gene.

3T3 Cells↗