Human mesangial cells express inducible macrophage scavenger receptor: an Ap-1 and ets mediated response.
BACKGROUND
Type A scavenger (SR) mediate the uptake of modified low-density lipoproteins by macrophages. The accumulation of lipid via this process is thought to lead to foam cell formation in atherosclerotic plaques. Human mesangial cells (HMC), which can be converted to foam cells in vivo, have not previously been shown to express SR in normal culture. We investigated whether or not there was an inducible form of SR in a human mesangial cell line (HMCL).


METHODS
SR activity was analyzed by cellular uptake of fluorescently labeled acetylated low-density lipoprotein using a flow cytometer. SR mRNA expression was examined using RT-PCR followed by Southern blotting. To investigate the molecular mechanism of SR expression, several reporter gene constructs were designed. The first contained a full SR promoter, the second a part of the SR promoter that has both activated protein-1 (AP-1) and ets transcriptional factor binding sites. Other constructs were identical to the second except they contained either AP-1 or ets motif mutations.


RESULTS
Phorbol 12-myristate 13-acetate (PMA) increased both the percentage of SR positive cells and SR mean fluorescence intensity. PMA also increased SR mRNA and promoter activity in a time and dose responsive manner. Function analysis showed that both AP-1 and ets motifs were specific response elements to PMA stimulation in HMCL.


CONCLUSIONS
The present study suggests that the combination of interaction between AP-1 and ets transcriptional factors may mediate the inducible expression of the SR gene in HMCL, which may contribute to foam cell formation.
Ruan
X Z
XZ
Center for Nephrology, Royal Free and University College Medical School, London, England, United Kingdom. rxz@rfhsm.ac.uk
Varghese
Z
Z
Powis
S H
SH
Moorhead
J F
JF
D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D005434:Flow Cytometry; D015870:Gene Expression / Q000187:drug effects; D005920:Glomerular Mesangium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D008077:Lipoproteins, LDL / Q000493:pharmacokinetics; D008264:Macrophages / Q000378:metabolism*; D008565:Membrane Proteins; D011401:Promoter Regions, Genetic / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D050783:Proto-Oncogene Proteins c-ets; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011971:Receptors, Immunologic / Q000235:genetics / Q000378:metabolism*; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D011993:Recombinant Fusion Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D051117:Scavenger Receptors, Class A; D051122:Scavenger Receptors, Class B; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
D008077:Lipoproteins, LDL; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D050783:Proto-Oncogene Proteins c-ets; D012333:RNA, Messenger; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D011993:Recombinant Fusion Proteins; C454739:Scarb1 protein, mouse; D051117:Scavenger Receptors, Class A; D051122:Scavenger Receptors, Class B; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D013755:Tetradecanoylphorbol Acetate