Coordinate augmentation in expression of genes encoding transcription factors and liver secretory proteins in hypo-oncotic states.
BACKGROUND
In the nephrotic syndrome (NS) proteins of intermediate size (40 to 200 kD) are lost into the urine resulting in a decrease in plasma albumin concentration and as a consequence a reduction in plasma colloid osmotic pressure (pi). Plasma pi has also been reported to be reduced in the condition of hereditary analbuminemia. The liver, in an apparent compensatory response, increases synthesis of a group of secreted proteins defending plasma pi. Regulation of several of these proteins, including both positive and negative acute phase proteins, is at the transcriptional level. This is the only known condition in which transcription of both positive and negative acute phase proteins (APPs) are increased simultaneously. The specific transcription factor(s) that might regulate this cascade is not defined.


METHODS
RNA was extracted from livers of 5 rats with hereditary analbuminemia (the Nagase analbuminemic rat, NAR), 5 rats with NS induced by adriamycin (Adria), 5 rats with NS caused by passive Heymann nephritis (NS) and 5 control animals. The concentrations of mRNAs encoding four secreted proteins (albumin, transferrin, fibrinogen, and apo A-1), five transcription factors, early growth response factor 1 (EGRF-1), HNF-4, NGFI-C, EGR-3, and Krox20 relative to two housekeeping genes, beta actin and GAPDH were determined simultaneously using kinetic reverse transcriptase polymerase chain methodology (kRT-PCR).


RESULTS
The levels of all mRNAs encoding secreted proteins except for albumin (which was reduced in NAR) were increased in NS and NAR and correlated significantly with one another. mRNA encoding EGRF 1 was increased fivefold in NS and NAR, and correlated significantly with mRNAs encoding Apo A-1, transferrin and albumin in the two NS groups. HNF-4 mRNA was increased approximately twofold in both NS groups and correlated with albumin (R = 0.881, P < 0.001), transferrin (R = 0.563, P = 0.012) and apo A-1 (R = 0.644, P = 0. 003). While fibrinogen mRNA correlated with that of each of the other secreted proteins, it did not correlate with either HNF-4 or EGRF-1 mRNA. Krox20, EGR3 and NGF1C were expressed at nearly undetectable levels.


CONCLUSIONS
The hepatic response in conditions characterized by reduced plasma pi include increased levels of mRNAs encoding a group of secreted proteins, including the negative APPs albumin, transferrin and apo A-1, and the positive APP fibrinogen. Levels of mRNAs encoding negative APPs and fibrinogen correlate with one another, suggesting that they are coordinately controlled. Both EGRF-1 and HNF-4 may regulate the expression of the negative APPs, which have increased transcription in hypo-oncotic states.
Kang
J
J
Department of Biological Chemistry, University of California, Davis 95616, USA.
Holland
M
M
Jones
H
H
Kaysen
G A
GA
D000118:Acetylglucosaminidase / Q000235:genetics; D000818:Animals; D016632:Apolipoprotein A-I / Q000235:genetics / Q000378:metabolism; D001796:Blood Protein Disorders / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D051766:Early Growth Response Protein 1; D051767:Early Growth Response Protein 2; D051776:Early Growth Response Protein 3; D005340:Fibrinogen / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D051557:Hepatocyte Nuclear Factor 4; D017874:Immediate-Early Proteins / Q000235:genetics; D007700:Kinetics; D008099:Liver / Q000737:chemistry / Q000378:metabolism*; D008297:Male; D009404:Nephrotic Syndrome / Q000235:genetics*; D009997:Osmotic Pressure; D010750:Phosphoproteins / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012045:Regulatory Sequences, Nucleic Acid; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012709:Serum Albumin / Q000172:deficiency*; D014157:Transcription Factors / Q000235:genetics*; D014168:Transferrin / Q000235:genetics / Q000378:metabolism
D016632:Apolipoprotein A-I; D004268:DNA-Binding Proteins; D051766:Early Growth Response Protein 1; D051767:Early Growth Response Protein 2; C486110:Egr1 protein, rat; C497328:Egr2 protein, rat; C497370:Egr3 protein, rat; D051557:Hepatocyte Nuclear Factor 4; D017874:Immediate-Early Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; D012709:Serum Albumin; D014157:Transcription Factors; D014168:Transferrin; D051776:Early Growth Response Protein 3; D005340:Fibrinogen; D000118:Acetylglucosaminidase