TRANSFORMING GROWTH-FACTOR-ALPHA (TGF-ALPHA) CONCENTRATIONS INCREASE IN REGENERATING RAT-LIVER - EVIDENCE FOR A DELAYED ACCUMULATION OF MATURE TGF-ALPHA

Changes in the concentration of transforming growth factor-alpha (TGFa lpha) protein were measured in regenerating liver. TGFalpha stimulates both DNA and protein synthesis in various liver-derived cells, and it s mRNA levels increase in liver after partial hepatectomy (PH), sugges ting that it may be an important autocrine regulator of liver regenera tion. Using a sheep antiserum raised against mature rat TGFalpha, we d eveloped a sensitive TGFalpha RIA. TGFalpha was extracted from livers in a detergent-containing buffer with protease inhibitors. Liver extra cts, to a volume of 10 mul/tube, produced a displacement curve of [I-1 25]TGFalpha that was parallel to the pure standard. The TGFalpha conte nt of normal liver was 57.04 +/- 26.25 pg/mg protein, 5.24 +/- 2.61 ng /mg DNA, and 10.33 +/- 4.47 ng/g liver (n = 5; mean +/- SD). Between 1 3-17 h after operation, TGFalpha concentrations in the livers of PH an imals increased over those in sham-operated (SH) controls (P < 0.05) a nd remained twice those in SH controls for more than 96 h, returning t o control values by 8 days. In unoperated liver, gel chromatography sh owed all TGFalpha immunoactivity to be in fractions corresponding to k nown TGFalpha precursors (15-30 kilodaltons). Mature 5.6-kilodalton TG Falpha was not detected until 48 h after PH and was still present at 9 6 h. These data support a role for TGFalpha in the response to PH in t he rat. However, the presence of TGFalpha precursors in normal liver, the short (<4-h) interval between the increase in TGFalpha concentrati ons and the onset of hepatocyte DNA synthesis, the sustained elevation of TGFalpha levels after DNA synthesis has ceased, and the lack of de tectable processing to the mature form until DNA synthesis has subside d all suggest that. the membrane-anchored precursor and the mature for ms of TGFalpha may have different functions, cellular sources, or targ et cells in regenerating liver.